Archive for the ‘Aircraft ownership and maintenance’ Category

The A&P Exam

Thursday, September 17th, 2015

Although I’ve been an aircraft owner since the late 1960s and heavily involved in GA maintenance since the late 1980s, I didn’t actually become an official card-carrying A&P mechanic until 2001. By the time I decided to go for my A&P ticket, I was already a pretty seasoned aircraft mechanic with a reputation for encyclopedic knowledge of aircraft systems and an aptitude for being able to troubleshoot thorny maintenance issues that had other mechanics stumped. I figured that passing the A&P exam would be a piece of cake.

I figured wrong.

An applicant for an A&P certificate must take and pass three multiple-choice 100-question knowledge tests.

An applicant for an A&P certificate must take and pass three multiple-choice 100-question knowledge tests.

By way of background, an applicant for an A&P certificate must surmount three sequential FAA-imposed hurdles. First, the applicant must prove to his FSDO that he has the minimum required experience performing maintenance on civil aircraft: 30 months on a full-time basis, or 4,800 hours on a part-time basis. Second, the applicant must take and pass three multiple-choice 100-question knowledge tests—mechanic general, mechanic airframe, and mechanic powerplant—and score at least 70% on each one. Third, the applicant must submit to an exhaustive (not to mention exhausting) oral and practical test with a Designated Mechanic Examiner—the mechanic’s equivalent to a checkride—which is normally at least a full-day affair.

When I started studying for the three A&P knowledge tests, my first surprise was the study syllabus, which struck me as being firmly anchored in the 1940s. For example, in preparing for the powerplant test, I reviewed more than 1,000 multiple-choice questions from the FAA’s “question bank” and found that the overwhelming emphasis was on radial engines, pressure carburetors, Hamilton Standard hydramatic propellers, and similar subjects of unquestionable interest to warbird buffs but of absolutely no relevance to contemporary GA aircraft of the sort that interested me. There were only a handful of questions about horizontally-opposed engines, perhaps two or three about fuel injection, only one about modern Hartzell compact hub propellers, and nothing at all about McCauleys.

The question bank for the powerplant test contained not a syllable about any technology that was less than 30 years old. Nothing about engine monitor data analysis, borescope inspections, spectrographic oil analysis, or scanning electron microscopy of oil filter contents. Nothing about compression ignition (Diesel) engines or electronic ignition systems or FADECs or lean-of-peak operation. Similarly, the airframe test was devoid of questions about composite construction (unless you count wood and fabric, which I suppose is the original composite).

To be fair to the FAA, there were actually lots of questions about “modern” 1960-vintage technologies, but they were all related to turbine and transport aircraft. To score a decent grade on the tests, it was obvious that I would need to master lots of material about turboprop and turbojet engines, air cycle machines, Roots blowers, and other esoterica that I knew I’d never remember or have any use for once the test was done.

Mastering the wrong answers

I took my three A&P knowledge tests at a local computerized testing center.

I took my three A&P knowledge tests at a local computerized testing center.

This was frustrating enough, but what really bugged me was that the “official FAA answer” to many of these multiple-choice questions was often the wrong answer. It became obvious that if I wanted to get a good score on the mechanic knowledge tests, I’d have to commit these “FAA answers” to memory even though I knew that they were the wrong answers.

Would you like to see some examples? Here are some actual questions from the 2001 FAA mechanic exam question bank, with the “official FAA answer” that would be used by the FAA to grade the exam:

#8072. Which fuel/air mixture will result in the highest engine temperature (all other factors remaining constant)?

A—A mixture leaner than a rich best-power mixture of .085.

B—A mixture richer than a full-rich mixture of .087.

C—A mixture leaner than a manual lean mixture of .060.

FAA-approved answer: C.

Discussion: Stoichiometric mixture (peak EGT) is around 15:1 or .067, so the FAA-approved answer C (“leaner than .060″ or about 17:1) would be very lean-of-peak, far leaner than most engines can run without unacceptable roughness (unless they are fuel-injected and have tuned fuel nozzles). This is definitely a mixture at which the engine would run cool, not hot. Of the three choices given, the “most correct answer” is A. The FAA-approved answer (C) is just plain wrong, and perpetuates the Old Wives’ Tale that rich mixtures are cool and lean mixtures are hot. With training like this, is it any wonder so many A&Ps blame almost every cylinder malady to LOP operation?

#8678. Why must a float-type carburetor supply a rich mixture during idle?

A—Engine operation at idle results in higher than normal volumetric efficiency.

B—Because at idling speeds the engine may not have enough airflow around the cylinder to provide proper cooling.

C—Because of reduced mechanical efficiency during idle.

FAA-approved answer: B

Discussion: None of the given answers is correct, but the FAA-approved one is the probably the worst possible choice, because it suggests that pilots should keep the mixture full-rich during idle and taxi in order to obtain proper cooling. Do you suppose that OWT explains why so many pilots taxi around at full-rich and foul the crap out of their spark plugs? Are they learning this from their A&Ps? Here’s the correct answer: “Because a very rich mixture is required for cold-starting, and aircraft carburetors don’t have a choke to provide such a rich mixture (the way automotive carbs do), so the idle mixture has to be set extremely rich … which is why as soon as the engine starts to warm up, you need to come back on the mixture control.” Of course, that answer isn’t one of the choices offered.

#8773. Carburetor icing is most severe at…

A—air temperatures between 30 and 40 degrees F.

B—high altitudes.

C—low engine temperatures.

FAA-approved answer: A

Discussion: Are you kidding me? The AOPA Air Safety Foundation briefing on carb ice states, “Icing is most likely to occur—and to be severe—when temperatures fall roughly between 50°F and 70°F and the relative humidity is greater than 60%.” It shows a gory photo of the fatal crash of a Cessna 182 caused by carb ice that formed at OAT 80°F and dewpoint 45°F. If the FAA genius who wrote this question was a pilot, it’s a sure bet that most of his experience is flying Gulfstreams, not Skylanes. (Keep in mind that to get a decent grade on the A&P knowledge test, you have to memorize these FAA-approved wrong answers, or risk failing!)

#8829. Which of the following defects would likely cause a hot spot on a reciprocating engine cylinder?

A—Too much cooling fin area broken off.

B—A cracked cylinder baffle.

C—Cowling air seal leakage.

FAA-approved answer: A

Discussion: Once again, the FAA offers three possible answers and then claims that the “wrongest” one is the one they consider correct. Every IA I’ve asked agrees with me that by far the most likely cause is a bad baffle (answer B), and none has ever seen a case where a cooling fin was broken off badly enough to create an issue.

#8982. If a flanged propeller shaft has dowel pins…

A—install the propeller so that the blades are positioned for hand propping.

B—the propeller can be installed in only one position.

C—check carefully for front cone bottoming against the pins.

FAA-approved answer: B

Discussion: Well that’s interesting. The Continental TSIO-520-BB engines on my 1979 Cessna T310R have flanged propeller shafts. Each flange has a pair of identical dowel pins spaced 180° apart. This permits my three-bladed McCauley C87 props to be installed in two possible orientations, one that results in the vertical blade pointing down when the engine stops, and the other that results in the vertical blade pointing up. According to the Cessna service manual, only one of these orientations is the correct one, so you need to be careful when installing the prop. The FAA-approved answer (B) is just plain wrong. So are the other two answers.

I could go on, but you get the idea.



Here’s irrefutable proof that I was able to remember all those FAA-approved wrong answers long enough to score 96, 99 and 99 on my three mechanic knowledge tests.

Well, it took me many hours of study, practice and drill to memorize all of the FAA-approved wrong answers to the thousands of multiple-choice questions in the question bank. As you can imagine, going through this mind numbing exercise was a character-building experience that greatly expanded my vocabulary (of expletives) and bolstered my respect for the cutting-edge mindset of our favorite friendly federal agency.

I guess I must’ve done a workmanlike job of studying and memorizing, because when I finally took the three FAA knowledge tests at my “Don’t try this at home, kids” LaserGrade computerized testing center, I scored 96% on the general and 99% on both the airframe and powerplant. (See Figure 1.) I don’t want to brag, but it’s a rare skill to master so many wrong answers so consistently in such a short period of time, if I do say so myself.

Once the exams were done and my scores were in the bag, I celebrated with the obligatory overnight soak of my brain’s medial temporal lobe (seat of long-term memory) in a 50-50 mixture of cheap champagne and methyl ethyl ketone, just to make absolutely sure all those FAA-approved wrong answers and Old Wives’ Tales were permanently purged from my gray matter. After all, it would certainly be embarrassing to inadvertently pass any of them on to the next generation of A&P mechanics, wouldn’t it?

Is Your Aircraft Okay to Fly?

Thursday, July 23rd, 2015

Who decides whether or not your aircraft is airworthy?

Airworthy steampEarlier this year, I wrote an article titled “Fix It Now…Or Fix It Later” that was published in a major general aviation magazine. The article discussed how to deal with aircraft mechanical problems that arise during trips away from home base. It offered specific advice about how pilots and aircraft owners can decide whether a particular aircraft issue needs to be addressed before further flight or whether it can safely wait until the aircraft gets back home. I considered the advice I offered in this article to be non-controversial and commonsense.

I was surprised when I received an angry 700-word email from a very experienced A&P/IA—I’ll call him “Damian” (not his real name)—condemning my article and accusing me of professional malfeasance in advising owners to act irresponsibly and violate various FARs. Damian’s critique started out like this:

After reading Mike Busch’s commentary “Fix It Now … Or Fix It Later,” I must take exception to most, if not all, the points made in his column. I believe his statements are misleading as to the operation of certified aircraft, to the point of being irresponsible for an A&P to suggest or imply that it’s up to the owner/operator whether or not to fly an aircraft with a known discrepancy. The FARs are quite clear on this matter, and there have been numerous certificate action levied on pilots who have operated aircraft with known discrepancies.

Damian went on to state that the FARs require that any aircraft discrepancy, no matter how minor, must be corrected and the aircraft approved for return to service “by persons authorized under FAR 43.7 (typically the holder of a mechanic certificate).” He went on to explain that the owner/operator may only approve for return to service those preventive maintenance items listed in FAR Part 43 Appendix A. He went on:

It should be noted that the FAA does not take into consideration the inconvenience or cost related to addressing a known discrepancy. Nor is it up to the owner/operator to determine the significance of a discrepancy as the FARs do not confer this discretion privilege to the owner/operator.

Damian’s attack on my article continued at great length, making it quite clear that his believe is that pilots and aircraft owners are mere “appliance operators” in the eyes of the FAA, and that only certificated mechanics are empowered to evaluate the airworthiness of an aircraft and determine whether or not it is legal and safe to fly. He ended his diatribe by saying:

I hope that others in the aviation community such as FAA Airworthiness Safety Inspectorss and aviation legal professionals weigh in on this commentary. I believe all will agree that this commentary is misleading and uninformed to the point of being irresponsible even to publish. At the very least, pilots that follows the advice of Busch’s commentary should enroll in the AOPA Pilot Protection Services plan because they’re likely to need it!

Whew! Strong stuff! If Damian is right, then the FAA had better lock me up and throw away the key. Fortunately for me, I believe he isn’t and (at least so far) they haven’t.

Where Damian Has It Wrong

Damian and I do agree on at least one thing: FAR 91.7 does indeed say quite unequivocally that it is a violation to fly an unairworthy aircraft, and that if the aircraft becomes unairworthy in flight, the PIC is obligated to discontinue the flight. I would never suggest for a moment that any pilot fly a known-unairworthy aircraft, at least without a ferry permit. That’s a no-brainer.

The much more difficult question is: Exactly how does the PIC decide whether or not an aircraft is airworthy or unairworthy, and therefore whether he is or isn’t allowed to fly it? On this question, Damian and I part company. In fact, his view and mine seem to be diametrically opposite.

Damian’s view is that almost any aircraft discrepancy requires the involvement of an A&P mechanic to evaluate and clear the discrepancy and approve the aircraft for return to service. I see absolutely nothing in the FARs to support such a position, particularly when it comes to non-commercial aircraft operated under Part 91.

To begin with, the basic airworthiness rule (FAR 91.7) is crystal clear about who is responsible for determining whether or not the aircraft may be flown. It says:

The pilot in command of a civil aircraft is responsible for determining whether that aircraft is in condition for safe flight.

The regulation places the burden squarely on the shoulders of the PIC. I don’t see anything there about A&Ps or repair stations having to be involved, do you?

Looking a bit deeper into the FARs, I can find only three circumstances under which a mechanic is required to get involved in making any sort of airworthiness determination on a Part 91 aircraft used for non-commercial purposes:

  1. Exactly once a year, FAR 91.409 requires that an annual inspection be performed by an A&P/IA or a Repair Station. But the other 364 days of the year, it’s the PIC who determines whether the aircraft is airworthy.
  2. When an Airworthiness Directive or Airworthiness Limitation becomes due, FAR 91.403 requires that a mechanic must certify that the AD or AL has been complied with (with rare exceptions where the PIC may do so).
  3. When an owner actually hires a mechanic to perform maintenance on an aircraft, in which case the mechanic is required to document his work and sign it off to testify that the work was performed properly. Note, however, that the mechanic’s signature in the logbook entry does NOT signify that the aircraft is airworthy, only that THE WORK PERFORMED by the mechanic was done in an airworthy fashion.

This third point is one that is frequently misunderstood by mechanics and owners alike. When I teach this stuff at IA renewal seminars, the hypothetical example I often use to illustrate this important point involves an owner who takes his aircraft to a mechanic for repair. The mechanic immediately observes that the aircraft has two obvious discrepancies: the right main landing gear tire is flat, and the left wing is missing. The owner asks the mechanic to fix the flat tire. The mechanic does so, makes a logbook entry describing the work he did on the right main landing gear, and signs it. His signature denotes only that the work he did (fixing the flat tire) was done properly. When the owner picks up the aircraft, the mechanic tells the owner, “I couldn’t help but notice that your left wing is missing. If you’ll permit me to offer you a word of friendly advice, I would not attempt to fly the aircraft until that issue is resolved.” But the missing left wing does not prevent the mechanic from signing the logbook entry. In fact, the mechanic is required by regulation to sign the logbook entry, regardless of whether the aircraft is airworthy or not. The mechanic’s signature addresses only the work performed by the mechanic, and nothing else.

The PIC’s Burden

If you’re on a trip and some aircraft discrepancy occurs – assuming the aircraft isn’t in the midst of its annual inspection and there’s no AD involved – it is up to you as PIC to determine whether or not that discrepancy makes the aircraft unairworthy or not. If you decide that it does, then you can’t fly the airplane until the airworthiness issue is rectified (and that might require hiring an A&P). On the other hand, if you decide that the discrepancy doesn’t rise to the level of making the aircraft unairworthy, then you’re free to fly home and deal with the issue later.

Under the FARs, it’s totally the PIC’s call. There’s no regulatory obligation for the PIC to consult a mechanic when making such airworthiness determinations. Having said that, however, it would certainly be a wise thing to do if you feel uncomfortable about making the decision yourself. It’s your call.

The FARs provide considerable help to the PIC in making such airworthiness determinations. FAR 91.213(d) describes a specific algorithm for deciding whether or not it’s okay to fly an airplane with various items of inoperative equipment. FAR 91.207 says that it’s okay to fly an aircraft with an inoperative ELT to a place where it can be repaired or replaced, no ferry permit required. FAR 91.209 says that position lights needn’t be working if you’re flying during daylight hours. And so on.

If your experience is anything like mine, what most of us call “squawks” are common occurrences, but the majority of them don’t rise to the level of being airworthiness items that cause us (in our capacity as PIC) to conclude that a fix is required before further flight. Even if you do encounter a genuine airworthiness problem – say a flat tire or dead battery or bad mag drop – that still doesn’t mean that you necessarily need to get a mechanic involved. The FARs provide (in Part 43 Appendix A) a list of roughly three dozen items that a pilot-rated owner or operator is permitted to perform and sign off on his own recognizance (without getting an A&P involved).

If you have a flat tire, for example, you (as a pilot-rated owner) are permitted to repair or replace it yourself. If you have a dead battery, you can charge it, service it, or even replace it. If you have a bad mag drop, the most common cause is a defective or fouled spark plug, and you’re permitted to remove, clean, gap, and replace spark plugs yourself. You are also allowed to make repairs and patches to fairings, cowlings, fabric (on fabric-covered aircraft), upholstery and interior furnishings. You can replace side windows, seat belts, hoses, fuel lines, landing and position lamps, filters, seats, safety wire, cotter pins, and more. You can even remove and install tray-mounted avionics from your panel.

Now, you might well prefer to hire an A&P to do some of these things rather than do them yourself, especially when on the road, far from your hangar and toolbox. I know I certainly would, and I’m an A&P myself. But Damian’s contention that you are compelled by the FARs to place your aircraft in the hands of an A&P any time any sort of discrepancy arises is simply not supported by the regulations.

Contrary to what Damian and many of his A&P colleagues may believe, the FAR’s place the responsibility for determining the airworthiness of the aircraft squarely on the PIC, except for once a year when an IA is required to make an airworthiness determination after performing an annual inspection

My colleague Mac McClellan pointed out to me that this closely resembles how the FAA determines whether a pilot is “airworthy.” One day every year or two or five, we pilots are required by regulation to go get an examination from an Aviation Medical Examiner who pronounces us medically fit to fly, or not. The remaining 364 or 729 or 1,824 days in between, the FAA expects us to self-certify that we’re medically fit. “Can you imagine,” Mac asked me rhetorically, “if we had to go to see an AME every time we got a sore throat or runny nose?”

The Back Door is Locked

Friday, June 12th, 2015

Cessna 210In my AOPA Opinion Leaders Blog post of September 2014 (“Backdoor Rulemaking?”), I discussed the unprecedented action taken by the Cessna Aircraft Company intended to compel the owners of cantilever-wing Cessna 210s to perform repetitive eddy-current inspections of their wing spars. Finally, I can fill you in on the punch line.

By way of background: Normally, if an aircraft manufacturer believes that an unsafe condition exists that justifies imposing special inspections, component life limits, replacement or overhaul times, or similar burdens on aircraft owners, they go to the FAA and ask for an Airworthiness Directive (AD) to be issued. If the FAA is persuaded that the alleged unsafe condition actually constitutes a significant safety concern and that the burden on owners is reasonable given the safety risk, then the FAA issues a Notice of Proposed Rulemkaing (NPRM) announcing its intention to issue an AD and soliciting comments on the proposal from the affected public. The FAA is then required to consider and respond to all public comments submitted during the comment period before issuing its final rule that makes the AD effective. This same notice-and-comment protocol is required of all executive-branch regulatory agencies of the U.S. federal government by a law called the Administrative Procedure Act (APA).

Indeed, that’s precisely what Cessna did in 2013: It asked the FAA’s Wichita Aircraft Certification Office (ACO) to issue an AD mandating repetitive eddy-current inspections on all cantilever-wing Cessna 210s. But to Cessna’s chagrin, the Wichita ACO turned down Cessna’s request and declined to proceed with an AD, presumably because the ACO was not persuaded that such an AD was justified.

That should have been the end of the matter. But it wasn’t.

In February 2014, Cessna very quietly published a revision to the Cessna 210 service manual that added three new pages to the manual. Those three pages constituted a new section 2B to the manual, titled “Airworthiness Limitations,” that called for the repetitive eddy-current spar inspections. Somehow Cessna persuaded the Wichita ACO to approve this amendment—something the ACO really shouldn’t have done, as you shall see.

Cessna then publicly took the position that compliance with the repetitive eddy-current spar inspections was compulsory because those inspections were now part of an FAA-approved Airworthiness Limitations Section (ALS). Indeed, FAR 91.403(c) compels aircraft owners to comply with mandatory replacement times, inspection intervals, and related procedures specified in an ALS. And FAR 43.16 compels maintenance personnel to perform any inspections or maintenance specified in an ALS precisely “by the book.”

David vs. Goliath?

SlingshotI first learned about this at the beginning of September 2014, when my colleague Paul New—owner of Tennessee Aircraft Services, Inc. (a well-known Cessna Piston Aircraft Service Center) and honored by the FAA in 2007 as National Aviation Maintenance Technician of the Year—discovered the new section 2B in the Cessna 210 service manual, and immediately realized its significance. Paul and I discussed the matter at length, and both felt strongly that Cessna’s actions could not be allowed to go unchallenged.

“If Cessna gets away with this,” I told Paul, “then any manufacturer will be able to effectively impose their own ADs whenever they want, bypassing the notice-and-comment protocol and the other safeguards built into the APA to protect the public from unreasonable government regulation.”

I helped Paul draft a letter to the Rulemaking Division (AGC-200) of the FAA’s Office of General Counsel, questioning the retroactive enforceability of Cessna’s newly minted ALS against Cessna 210s that were manufactured prior to the date the ALS was published (i.e., all of them, given that Cessna 210 production ceased in 1986). Our letter questioned whether Cessna could do what it was trying to do (i.e., make the eddy-current inspections compulsory) within the confines of the APA. We asked AGC-200 to issue a formal Letter of Interpretation (LOI) of the thorny regulatory issues that Cessna’s unprecedented actions raised.

And then we waited. And waited.

AGC-200 initially advised us that they had a four-month backlog of prior requests before they would be able to respond to our request. In fact, it took seven months. It turns out that our letter questioning the enforceability of Cessna’s ALS opened a messy can of worms. AGC-200 assigned two attorneys to draft the FAA’s response, and they wound up having to coordinate with AFS-300 (Flight Standards Maintenance Division), AIR-100 (Aircraft Certification Division), ACE-100 (Small Airplane Directorate), and of course ACE-115W (Wichita Aircraft Certification Office) who mistakenly approved Cessna’s ALS in the first place.

FAA Legal Does the Right Thing

FAA Headquarters

FAA Headquarters
800 Independence Ave.
Washington DC

Finally, on May 21, 2015, AGC-200 issued the Letter of Interpretation (LOI) that we requested. It was five pages long, and was everything we hoped it would be and more. It slammed shut the “rulemaking backdoor” that Cessna had been attempting to use to bypass the AD process, locked it once and for all, threw away the key, and squirted epoxy glue in the lock for good measure. You can read the entire LOI in all its lawyerly glory, but here’s the CliffsNotes version of the letter’s key bullet points:

  • Under FAR 21.31(c), an ALS is part of an aircraft’s type design.
  • The only version of an ALS that is mandatory is the version that was included in the particular aircraft’s type design at the time it was manufactured.
  • Absent an AD or other FAA rule that would make the new replacement times and inspection intervals retroactive, Cessna’s “after-added” ALS is not mandatory for persons who operate or maintain the Model 210 aircraft, the design and production of which predate the new ALS addition. The “requirements” set forth in the ALS would only be mandatory for aircraft manufactured after the ALS was issued. And of course, production of the Cessna 210 ceased in 1986.
  • If operational regulations were interpreted as imposing an obligation on operators and maintenance providers to comply with the latest revision of a manufacturer’s document, manufacturers could unilaterally impose regulatory burdens on operators of existing aircraft. This would be legally objectionable in that the FAA does not have legal authority to delegate its rulemaking authority to manufacturers. Furthermore, “substantive rules” can be adopted only in accordance with the rulemaking section of the APA (5 U.S.C. § 553) which does not grant rulemaking authority to manufacturers. To comply with these statutory obligations, the FAA would have to engage in its own rulemaking to mandate the manufacturer’s document, as it does when it issues ADs.

The bottom line is this: Manufacturers of certificated aircraft* are not permitted to impose regulatory burdens on aircraft owners by changing the rules in the middle of the game. Only the FAA may do that, and only through proper rulemaking action that complies with the APA (including its notice-and-comment provisions and other safeguards). If you ever encounter a situation where the manufacturer of your aircraft tries to do this, call their cards—the FAA lawyers will back you up.

*NOTE: The rules are completely different for S-LSAs.  The manufacturers of S-LSAs can do pretty much anything they like, and their word is the law. (A seriously flawed situation IMHO.)

The LOI concluded with the following surprising paragraph:

On February 19, 2015, the FAA’s Small Airplane Directorate sent a letter to Cessna that addressed some of the above issues, and pointed out the non-mandatory nature of the after-added ALS for the Model 210 aircraft. The FAA asked Cessna to republish the replacement times and inspections as recommendations that are encouraged, but optional, for those in-service aircraft, unless later mandated by an AD. To date [three months later –mb] Cessna has not provided a written response outlining its position on this matter.

Are we having fun yet?

When to say “no” to maintenance

Wednesday, May 13th, 2015

Ken is the proud owner of a late-model high-performance single-engine airplane. It’s a gorgeous machine, with wall-to-wall glass in the cockpit, a big turbocharged engine, 500 hours on the Hobbs meter, almost no squawks, and still under factory warranty on both engine and airframe. So when Ken took it to a well-known factory-authorized service center for its annual inspection, he expected that it would be relatively painless. Imagine his shock when the shop presented him with an estimate of more than $8,500. That’s when he called me for advice.

I reviewed the shop’s estimate. It started out with a flat-rate charge for the annual inspection (performed in accordance with the manufacturer’s annual inspection checklist) of $2,850. This was 30 hours of labor at the shop’s rate of $95/hour, which in my experience was right on target for this make and model.

Probing deeper

The next item that caught my eye was a $200 estimate for cleaning the engine’s fuel injector nozzles. I used to do such prophylactic nozzle cleaning on my own airplane until about 10 years ago, when I had an illuminating discussion with George Braly (of GAMI and Tornado Alley Turbo fame), who is arguably the world’s expert on fuel nozzles. George pointed out to me that there’s no valid reason to do such periodic nozzle cleaning, because the nozzles do not get dirty in service (since they are continuously being cleaned by a very effective solvent). He told me that in his experience with many thousands of GAMIjector nozzles, virtually all clogged nozzle events occurred shortly after maintenance during which the fuel system was opened up and some foreign material got into the system. That resonated with me, because in the first 12 years I owned my Cessna T310R, I experienced two clogged-nozzle episodes, and both occurred right after maintenance due to grease getting into the fuel system. So I stopped cleaning my nozzles 10 years ago, and haven’t had a clogged nozzle since. I advised Ken to decline the nozzle cleaning.

There was a $300 estimate to replace the O-rings on the brake calipers. I asked Ken whether he had spongy brakes or had any evidence of brake fluid leakage at the calipers. He said no. I suggested he decline the O-ring replacement.

Continental S-20 magnetoThere was a $1,700 estimate for “4-year overhaul of pressurized mags”—$700 for each magneto plus 3 hours to remove and reinstall. The aircraft is equipped with Continental S-20 mags, and the Continental Ignition System Master Service Manual X40000 calls for a 500-hour IRAN (inspect and repair as necessary), not an overhaul. The IRAN typically costs $300 to $400 per mag, depending on what parts need to be replaced. I suggested that Ken instruct the shop to do the 500-hour IRAN instead of the overhaul exchange, which would knock about $700 off the invoice.

There was a $400 estimate to replace the magneto pressurization filter. The filter is clear plastic (actually tinted green) so you can inspect it and see if it needs to be changed. It was clean as a whistle. I suggested that Ken decline the filter change.

Teledyne-Gill G-243 batteryNext was a $800 estimate to replace the battery. The aircraft manufacturer’s checklist recommends replacing it every two years, and Ken’s was two years old. But the battery manufacturer (Teledyne-Gill) recommends doing an annual capacity test and replacing the battery only when its capacity falls below 80% of specs. Using the capacity-test method, these batteries typically last 3 to 5 years before flunking the test. Another thing that bothered me was that the battery—a Gill G-243—cost $395 at Aircraft Spruce, but was listed on the estimate as costing $774. Now I don’t have a problem with shops making a fair profit on the parts they install, but marking up a $395 battery to $774 struck me as a bit much. So I suggested that Ken decline the battery change, wait until the battery flunks its capacity check, and then consider buying the battery and installing it himself.

Then there was a $320 estimate to change the filter in his TKS anti-icing system. The manufacturer recommends changing this filter every 2 years (and his was 2 years old), but in hundreds of filters changed we’ve never seen one that wasn’t spotlessly clean. The shop agreed with this observation. I advised Ken that unless he had some reason to believe someone dumped a Diet Coke into his TKS tank, he should decline the TKS filter change.

Bottom line

Ken called the service center and politely declined the various items that I’d recommended. Ken reported that the shop’s Director of Maintenance had no problem complying with Ken’s instructions, and the invoice wound up some $3,000 lower than it would have been otherwise. That’s enough to buy a fair amount of 100LL, even at today’s prices.

Now many of you are probably thinking that this service center was trying to rip Ken off, and he should never take his airplane back there again. I disagree.

Gavel + wrenchIn today’s litigious world, any mechanic or shop that doesn’t recommend following the manufacturer’s guidance to the letter risks being sued and taken to the cleaners if anything goes wrong. Therefore, in my view, Ken’s service center was almost compelled to present Ken with the estimate that they did. Call it “defensive maintenance” or “CYA” if you wish, but it’s the way things are in today’s post-GARA, non-tort-reform world.

The way I see it, the responsibility for “just saying no” to these over-the-top maintenance recommendations lies with the aircraft owner, not the shop. If the aircraft owner instructs the shop (in writing) that he declines some manufacturer-recommended maintenance task, that takes the shop off the liability hook and allows them to do things the way the owner wants them done without fear of being sued.

Therefore, if an owner wants to avoid paying through the nose for such defensive maintenance, he needs to learn when to say no.

When to say no

Learning when to say no takes a good deal of knowledge and experience, but there are some basic rules. The most important rule is that you never say no to any maintenance procedure that is required by regulation. For example, FAR Part 43 Appendix D requires that every annual inspection on a piston aircraft must include a compression test of the cylinders, cutting open the oil filter to inspect for metal, and running up the engine to check that critical engine operating parameters (oil pressure, static RPM, etc.) are within normal limits. Mechanics are also required to comply with any “Airworthiness Limitations” contained in the manufacturer’s service manual or ICAs. Any applicable Airworthiness Directives must be complied with. All these things are non-negotiable.

Airworthiness definedIt’s also best to avoid saying no to proposed repairs that the inspecting A&P/IA considers to be “airworthiness items.” Those are generally discrepancies that he considers to be safety-of-flight items, and will not be comfortable approving the aircraft for return to service until they are corrected. But don’t be fooled. Many of the items that I suggested Ken decline were listed on the shop’s estimate as “Airworthy Item,” yet when Ken instructed the shop not to do them, they accepted his direction without argument. So just because an item is listed on the estimate as an airworthiness item doesn’t necessarily mean that it really is one. When in doubt, say no and see how the IA responds. If he tells you he’s not comfortable signing off the annual unless you approve the repair, then it’s time to re-think your position.

Good candidates for saying no to include time-directed maintenance recommendations for things that can be readily done on-condition instead. Ken’s battery, pressurization filter, brake O-rings and TKS filter are good examples. (So are most engine and propeller TBOs in my opinion, but not everyone agrees with me.) Consider ignoring the time recommendations and replace or repair these items only when inspection shows that they need to be replaced or repaired. We should only be maintaining things on time (like the 500-hour magneto IRAN) if there’s no practical way to maintain them on-condition.

Also consider saying no to preventive maintenance items intended to prevent failures whose consequences you consider acceptable. For example, replacing your vacuum pump every 500 hours (per the manufacturer’s recommendation) is silly if you have dual vacuum pumps or a standby vacuum system or a backup electric attitude indicator. If a vacuum pump failure doesn’t affect safety of flight, why not simply run it to failure and then replace it? Ditto if you have dual alternators.

Finally, consider saying no to an overhaul if an IRAN will do the job (as with Ken’s mags), and consider saying no to replacing anything that can be repaired instead.

The art of saying no is definitely an acquired skill, but one that can save you a small fortune in reduced maintenance costs once you get the hang of it. Like any acquired skill, practice makes perfect.

How to destroy your engine in one minute

Monday, April 13th, 2015

At least once a year for as long as I can remember, I have been contacted by an aircraft owner whose piston aircraft engine was destroyed or severely damaged by a destructive detonation or pre-ignition event. In one recent 12-month period, I encountered three such incidents.

One incident involved British Cirrus SR-20 powered by a 200 horsepower Continental IO-360-ES engine. The plane was equipped with an Avidyne Entegra MFD with an integrated engine monitoring system called “EMAX.”

The CHT data downloaded from the EMAX system tells the short story of this engine’s demise:

SR-20 pre-ignition event

Click on image to open a higher-resolution version.

Everything looked fine until about two minutes after the pilot applied takeoff power, at which point the #1 cylinder’s CHT began to climb rapidly compared to the other five cylinders. At the three-minute mark after brake release—with the aircraft at roughly 2,000’ AGL—CHT #1 rose above 400°F and set off a high-CHT alarm on the MFD.

CHT #1 continued its rapid rise—nearly 1°F per second—that continued unabated until the piston and cylinder head were destroyed approximately five minutes after takeoff power was applied and two minutes after the CHT alarm was displayed. At that point, since the cylinder was no longer capable of combustion, CHT #1 started plummeting.

We can’t be sure just how hot CHT #1 got because the Avidyne EMAX system “pegs” at 500°F. A reasonable guess is that the CHT peaked somewhere between 550°F and 600°F. No cylinder or piston can tolerate such conditions for very long, and this one obviously didn’t.


Not long after CHT #1 went off-scale on the MFD, the pilot realized something was very wrong, and pulled the power way back. But he was a couple of minutes late, and the engine was already toast. Here’s what the #1 piston looked like after the event:

Piston with corner melting

Click on image for higher-resolution version.

Note the melted corners of the piston crown, the destruction of the top compression ring lands, and the severe metal erosion above the piston pin. (Much of this molten metal wound up inside the crankcase and contaminated the bearings and oil passages.) Also note the severely hammered appearance of the piston crown, the classic signature of heavy detonation. The cylinder head was found to have a big chunk of metal missing from it. Both spark plugs were destroyed by the event as well.

This engine was a low-time Continental factory engine, so the owner figured that the severe engine damage would be covered under Continental’s warranty. I advised him not to bother filing a warranty claim, because I’ve never known Continental to give warranty consideration for a destructive detonation or pre-ignition event. Continental considers this to be operational abuse, not a defect in materials or workmanship, and therefore not covered by warranty. (For what it’s worth, I agree with Continental’s position on this.) The owner didn’t believe me and filed a warranty claim anyway. Continental promptly and unequivocally denied the claim, just as I predicted.

The moral of the story is that it is important for aircraft owners to have a good digital engine monitor installed, to know the telltale symptoms of destructive detonation and pre-ignition, and to act fast when those symptoms appear. You may have less than one minute to react if you want to save your engine.

Another incident

Here’s another similar case that occurred to a Beech Bonanza very shortly after takeoff. The annotated JPI data for this event is courtesy of General Aviation Modifications Inc. (GAMI):

Preignition event

Click on image for a higher-resolution version.

This time, it was the #5 cylinder that experienced thermal runaway and pre-ignition. It was an even more severe event than the one suffered by the Cirrus, and took only two minutes from the application of takeoff power to the complete destruction of the #5 piston, which wound up with a large hole melted through the piston crown:

Holed Piston

Click on image for a higher-resolution version.

Now that’s ugly!

In yet another case (for which I unfortunately have no photos), a drop-dead gorgeous Lancair IV-P kitplane powered by a fire-breathing 350-hp TCM TSIO-550 engine went up for its first test flight after 10 years of laborious building time by the owner. Within minutes, the airplane was back on the ground with an engine that was totally destroyed. A forensic post-flight evaluation revealed that the magnetos had been timed approximately 10 degrees advanced from the proper timing. That turned out to be a $50,000 mistake.

The Lancair’s instrument panel was wall-to-wall glass, including an ultra-sophisticated digital engine monitoring system. The engine monitor was literally crying out for attention throughout the short test flight, but the test pilot never noticed its warnings until the engine cratered.

What causes this?

There are a number of things that can cause or contribute destructive events like these. I’ve already mentioned one: advanced ignition timing. It’s astonishing how often we see engines with the magneto timing advanced several degrees from spec. (E.g., 25° BTDC when the engine data plate calls for 22° BTDC.) Even a couple of degrees is enough to significantly reduce the detonation margin of the engine. Add a hot day and perhaps a cooling baffle that isn’t quite up to snuff, and BOOM!

Owners should be particularly alert for mis-timed magnetos whenever maintenance is done that involves magneto removal or adjusting magneto timing. (More often than not, these occur during the annual inspection.) If mag timing is advanced, you’ll notice that your EGTs are lower and your CHTs are higher than what you were seeing prior to maintenance. (Retarded timing results in the opposite: higher EGTs and lower CHTs.) If you notice this after the airplane comes out of maintenance, take it back to the shop and have the mag timing re-checked. It’s a quick check and could save your engine (not to mention your gluteus maximus). Magnetos are required to be timed within one degree of the timing specified on the engine’s data plate, and any error should be in the retarded direction.

MP and FF guage comboAnother common culprit is inadequate fuel flow on takeoff. When taking off from a near-sea-level airport—or from any elevation if you’re flying a turbocharged airplane—you need to see fuel flow that’s right up against the red-line on the gauge (or the maximum fuel flow shown in the POH). Unlike most other gauges on your panel, hitting red-line on the fuel-flow gauge (or even going a smidgen over) is a good thing, not a bad thing. Takeoff fuel flow is a lot like tire pressure—a bit too much is a whole lot better than a bit too little. Anything less than red-line fuel flow on takeoff reduces the engine’s detonation margin, and significantly less can reduce it enough to cause a catastrophic event.

Not long ago, a client of my maintenance-management firm had a prop-strike incident that required a teardown inspection of the engine. When the inspection was complete and the engine was reinstalled in the airplane, the owner picked up the airplane from the engine shop and flew it back to his home base airport. Upon arriving there, he informed us that the fuel flow was 3 GPH below red-line on takeoff, and asked that we schedule a service appointment to have the fuel flow adjusted.

I was flabbergasted. What was this owner thinking? Why didn’t he abort the takeoff immediately when he noticed that the fuel flow was 3 GPH short, and ask the engine shop to adjust it? Why would he fly the airplane home in that condition? What part of “inadequate detonation margin” didn’t he understand?

Yet another cause is a partially clogged fuel injector nozzle. This can occur anytime, but most frequently occurs shortly after the aircraft comes out of maintenance because that’s the most likely time for foreign material to get into the fuel system. (I’ve had two serious clogged-nozzle episodes in my airplane over the past 25 years, and both occurred shortly after an annual inspection.)

Save your engine!

ThrottleRegardless of the cause, the solution is not rocket science. There are two simple rules that will almost always prevent these sorts of destructive events from occurring:

First, check your fuel flow gauge early on every takeoff roll. If the fuel flow is not at red-line or very close to it, reject the takeoff and sort things out on the ground. (The exception is takeoffs at high density altitudes in normally-aspirated airplanes, and detonation is quite unlikely under those conditions.)

Second, set your engine monitor CHT alarm to 400°F or less for Continental engines and 420°F or less for Lycoming engines. (On my own Continental-powered airplane, I have my alarm set to 390°F.) When the alarm goes off, do whatever it takes right now to bring the CHT back down below 400°F. Verify that the mixture is full-rich. Turn on the boost pump if it isn’t already on. Open the cowl flaps if you have them. And if CHT triggers the alarm and appears to be rising rapidly, throttle back aggressively to stop the thermal runaway. Don’t be shy about doing these things immediately, because you may only have a minute or two to act before your engine craters.

(Oh, and if your airplane isn’t equipped with a digital engine monitor with CHT alarm capability, do yourself a favor and install one. Trust me, it’ll pay for itself quickly.)

When you get on the ground, put the airplane in the shop and have the spark plugs removed and inspected for damage, the cylinders borescoped, and the magneto timing checked. If takeoff fuel flow was short of red-line, have it adjusted before further flight.

Champion Aerospace: From Denial to Acceptance

Thursday, March 19th, 2015

Champion Aviation Spark PlugsAccording to the model popularized by Dr. Elisabeth Kübler-Ross in her seminal 1969 book On Death & Dying, there are five stages of grief: denial, anger, bargaining, depression, and acceptance. This is apparently what Champion Aerospace LLC has been going through over the past six years with respect to the widely reported problems with the suppression resistors in its Champion-brand aviation spark plugs. I last discussed this issue in my August 2014 blog post Life on the Trailing Edge.

I first became aware of the Champion spark plug resistor problem in 2010, although there’s evidence that it dates back to 2008. We were seeing numerous cases of Champion spark plugs that were causing bad mag drops, rough running and hard starting even though they looked fine and their electrodes weren’t worn anywhere near the retirement threshold. The thing these spark plugs had in common were that they were all Champion-brand plugs and they all measured very high resistance or even open-circuit when tested with an ohmmeter.

We also saw a number of cases where high-resistance Champion plugs caused serious internal arc-over damage to Slick magnetos (mostly in Cirrus SR20s). If the damaged mag was replaced without replacing the spark plug, the new mag would be damaged in short order. The cause-and-effect relationship was pretty obvious.

In researching this issue, I looked at the magneto troubleshooting guide on the Aircraft Magneto Service website, maintained by mag guru Cliff Orcutt who knows more about aircraft ignition systems than just about anyone I know. Cliff owns and operates my favorite mag specialty shop, and that’s where I send the mags on my own airplane every 500 hours for inspection and tune-up. In reading Cliff’s troubleshooting guide, I came across the following pearls of wisdom:

  • Take an OHM Meter and measure the resistance value from the connection in the bottom of the barrel to the clean center electrode at the firing end, electrode must be bare metal.
  • A new Champion plug will have a value of 800 to 1200 OHMS. New Tempest (formerly Unison-Autolite) will measure 1000 OHMS.  Replace any plug above 5000 OHMS.
  • A spark plug bomb tester can test a bad plug and lead you to conclude it is serviceable. The OHM Meter check is simple, readily available, and amazingly accurate in finding misfiring plugs.

We started asking the maintenance shops we hired to maintain our clients’ aircraft to ohm out the plugs at each 50-hour spark plug maintenance cycle. The number of plugs that measured over 5,000 ohms was eye-opening. Many plugs measured tens or hundreds of thousand ohms, and it wasn’t unusual to find plugs that measured in the megohm range or even totally open-circuit. Here, for example, is a set of 12 Champion plugs removed for cleaning and gapping from a Cirrus SR22 by a shop in South Florida:

Champion spark plug resistance

Notice that only two of these 12 plugs measured less than 5K ohms, and one of those had to be rejected because its nose core insulator was cracked (a separate issue affecting only Champion fine-wire spark plugs, and unrelated to the resistor issue that affected all Champion plugs).

Why spark plugs have resistors

Worn spark plug

A worn-out spark plug.

Early aviation spark plugs didn’t contain resistors. They didn’t last long, either. The reason was that each time the plug fired, a significant quantity of metal was eroded from the electrodes. Magnetos fire alternate spark lugs with alternate polarities, so half of the plugs suffered accelerated erosion of their center electrodes, and the other half suffered erosion of the ground electrodes. Eventually, the ground electrodes became so thin or the center electrode became so elliptical that the plug had to be retired from service.

Spark plug manufacturers found that they could extend the useful life of their plugs by adding an internal resistor to limit the current of the spark that jumps across the electrodes. The higher the resistance, the lower the current. And the lower the current, the less metal eroded from the electrodes and the longer the plug would last before the electrodes got so worn that the plug had to be retired.

Adding a resistor to the plug also raised the minimum firing voltage for a given electrode gap. The result is a hotter, more well-defined spark that improves ignition consistency and reduces cycle-to-cycle variation.

The value of the resistor was fairly critical. If the resistance was too high, the plug would fire weakly, resulting in engine roughness, hard starting, excessive mag drops, and (if the resistance was high enough) arc-over damage to the magneto and/or harness. If the resistance was too low, the plug electrodes would erode at an excessive rate and its useful life would be short. Experimentation showed that a resistance between 1K and 4K ohms turned out to be a good compromise between ignition performance and electrode longevity. Brand new Champion-brand aviation spark plugs typically measure around 1,200 ohms fresh out of the box. New Tempest-brand plugs typically measure about 2,500 ohms. Both of these represent good resistance values right in the sweet spot.


As word of these erratic and wildly out-of-spec resistance values began reaching aircraft owners and mechanics (primarily via the Internet), Champion went on the defensive. At numerous aviation events and IA renewal seminars, Champion reps dismissed the significance of resistance measurements. They explained that the silicon carbide resistor in Champion-brand plugs is made to show the proper resistance whenever a high-voltage pulse is present, and can’t necessarily be measured properly with an ohmmeter. Further, they stated that the proper way to test a spark plug is on a spark plug testing machine (so-called “bomb tester”), and claimed that if a plug functions well during a bomb test, it should function well in the airplane.

Champion old insulator assembly

Champion old insulator assembly.

Of course, this “company line” from Champion didn’t agree with our experience. We’d seen numerous instances of high-resistance Champion plugs that tested fine on the bomb tester but functioned erratically in service. Nor did it agree with the Mil Spec for aviation spark plugs (MIL-S-7886B) which states clearly:

4.7.2 Resistor. Each spark plug shall be checked for stability of internal resistance and contact by measurement of the center wire resistance by the use of a low voltage ohmmeter (8 volts or less). Center wire resistance values of any resistor type spark plug shall be as specified in the manufacturer’s drawings or specifications. 

One enterprising Cessna 421 owner named Max Nerheim performed high-voltage testing of Champion spark plugs, and found that plugs that measure high-resistance or open-circuit with a conventional ohmmeter also had excessive voltage drop when fired with high voltage, and required a higher minimum voltage to produce any spark. Max Nerheim wasn’t just an aircraft owner, mind you, he was also Vice President of Research for TASER International, Inc. and was exceptionally qualified to perform high-voltage testing of Champion spark plugs. Nerheim’s findings flatly contradicted Champion’s company line, and agreed with what we were seeing in the field. Nerheim also disassembled the resistor assemblies of a number of high-resistance Champion plugs and found that the internal resistor “slugs” were failing.


What's your resistance?The spit really hit the fan when Champion’s primary competitor in the aviation spark plug space, Aero Accessories, Inc., launched a marketing campaign to promote sales of its Tempest-brand aviation spark plugs by highlighting the resistance issue. (Aero Accessories acquired the Autolite line of aviation spark plugs from Unison Industries in 2010, an re-branded them under its Tempest brand.) In February 2013, they issued a Tempest Tech Tip titled “The Right Way to Check Spark Plug Resistors,” started selling a fancy spark plug resistance tester, and launched a big “What’s Your Resistance” advertising campaign in the general aviation print media.

Predictably, this provoked a rather hostile response from Champion. Their field reps ratcheted up their public relations campaign claiming that the ohmeter check was meaningless, and insisting that Champion spark plugs didn’t have a resistance problem that affected the performance of their plugs.


In the face of both overwhelming technical evidence from the field that their spark plugs had a resistor problem, and a virtual blitzkrieg from their principal competitor that was starting to erode their dominant market share, Champion began having some self-doubts. Max Nerheim discussed his high-voltage test findings with Kevin Gallagher, Manger of Piston and Airframe at Champion Aerospace, and Gallagher acknowledged that Champion was looking into the issue with the resistor increasing in impedance, but did not have it resolved yet. Meanwhile, the Champion field reps continued to insist to anyone who would listen that claims of resistor problems in Champion spark plugs were false and that the ohmmeter test was meaningless.


Sometime in late 2014, it appears that Champion very quietly changed the internal design of their spark plugs to use a sealed, fired-in resistor element that appears to be quite similar to the design of the Tempest/Autolite plug. They didn’t change any part numbers. So far as I have been able to tell, they didn’t even issue a press release. The Champion Aerospace website makes no mention of any recent design changes or product improvements. But the cutaway diagram of the Champion spark plug now on the website shows the new fired-in resistor. Here are the old and new cutaway diagrams. Compare them and you’l clearly see the difference.

Click on images below to see higher-resolution versions.

Champion spark plug cutaway (old)

Champion spark plug cutaway (old)

Champion spark plug cutaway (new)

Champion spark plug cutaway (new)

I checked with a number of A&P mechanics and they verified that the latest Champion spark plugs they ordered do indeed have the new design. It’s easy to tell whether a given Champion spark plug is of the old or new variety. Simply look at the metal contact located at the bottom of the “cigarette well” on the harness end of the plug. The older-design plugs have a straight screwdriver slot machined into the metal contact, while the newer-design plugs do not.

As I write this, it’s still too early to tell whether Champion’s quiet resistor redesign will cure the drifting resistance problem, but my best guess is that it will. If I’m right, this is very good news indeed for users of Champion aviation spark plugs. I applaud Champion Aerospace for improving its product.

Still, I can’t help but wonder why it took six years for the company to work through its grief from denial to acceptance. I suppose grief is a very personal thing, and everyone deals with it differently.

Owner in command

Tuesday, February 17th, 2015

Every pilot understands the notion of “pilot in command.” That’s because we all had some certificated flight instructor (CFI) who mercilessly pounded this essential concept into our heads throughout our pilot training. Hopefully, it stuck.

As pilot-in-command (PIC), we are directly responsible for, and the final authority as to, the operation of our aircraft and the safety of our flight. Our command authority so absolute that in the event of an in-flight emergency, the FAA authorizes the PIC to deviate from any rule or regulation to the extent necessary to deal with that emergency. (14 CFR §91.3)

In four and a half decades of flying, I’ve overheard quite a few pilots dealing with in-flight emergencies, and have dealt with a few myself. It makes me proud to hear a fellow pilot who takes command of the situation and deals with the emergency decisively. Such decisiveness is “the right stuff” of which PICs are made, and what sets us apart from non-pilots.

Conversely, it invariably saddens me to hear a frightened pilot abdicate his PIC authority by throwing himself on the mercy of some faceless air traffic controller or flight service specialist to bail him out of trouble. How pathetic! The ATC or FSS folks often perform heroically in such “saves,” but few of them are pilots, and most have little or no knowledge of the capabilities of the emergency aircraft or its crewmember(s). They shouldn’t be placed in the awful position of having to make life-or-death decisions on how best to cope with an in-flight emergency. That’s the PIC’s job.

Fortunately, most of us who fly as PIC understand this because we had good CFIs who taught us well. When the spit hits the fan, we take command almost instinctively.

Owner in command

When a pilot progresses to the point of becoming an aircraft owner, he suddenly takes on a great deal of additional responsibility and authority for which his pilot training most likely did not prepare him. Specifically, he becomes primarily responsible for maintaining his aircraft in airworthy condition, including compliance with all applicable airworthiness requirements including Airworthiness Directives. (14 CFR §91.403) Unfortunately, few owners have the benefit of a Certificated Ownership Instructor (COI) to teach them about their daunting new responsibilities and authority as “owner in command” (OIC).

Consequently, too many aircraft owners fail to comprehend or appreciate fully their weighty and complex OIC responsibilities. They put their aircraft in the shop, hand over their keys and credit card, and tell the mechanic to call them when the work is done and the airplane is ready to fly. Often, owners give the mechanic carte blanche to “do whatever it takes to make the aircraft safe,” and don’t even know what work is being performed or what parts are being replaced until after-the-fact when they receive a maintenance invoice.

In short, lots of owners seem to act as if the mechanic is responsible for maintaining the aircraft in airworthy condition. But that’s bass-ackwards. In the eyes of the FAA and under the FARs, it’s the owner who is responsible. The mechanic is essentially “hired help”—a skilled and licensed contractor hired to assist the owner carry out his regulatory responsibilities.

General Contractor

An aircraft owner-in-command acts as the “general contractor” for the maintenance of his aircraft.

I find it helpful to compare the proper role of the aircraft owner in maintaining an airworthy aircraft to that of a general contractor in building a house. The general contractor needs to hire licensed specialists—electricians, plumbers, roofers, masons, and other skilled tradesmen—to perform various tasks required during the construction. He also needs to hire a licensed building inspector to inspect and approve the work that the tradesman have performed. But, the general contractor makes the major decisions, calls the shots, keeps things within schedule and budget constraints, and is held primarily accountable for the final outcome.

Similarly, an aircraft owner hires certificated airframe and powerplant (A&P) mechanics to perform maintenance, repairs and alterations; certificated inspectors (IAs) to perform annual inspections, and other certificated specialists (e.g., avionics, instrument, propeller and engine repair stations) to perform various specialized maintenance tasks. But, the owner is the boss, is responsible for hiring, firing, and managing these various “subcontractors,” and has primary responsibility for the ensuring the desired outcome: a safe, reliable aircraft that meets all applicable airworthiness requirements, achieved within an acceptable maintenance budget and schedule.

Who’s the boss?

The essence of the owner-in-command concept is that the aircraft owner needs to remain in control of the maintenance of his aircraft, just as the pilot needs to remain in control of the operation of the aircraft in-flight. When it comes to maintenance, the owner is supposed to be the head honcho, make the major decisions, ride herd on time and budget constraints, and generally call the shots. The mechanics and inspectors and repair stations he hires are “subcontractors” with special skills, training and certificates required to do the actual work. But the owner must always stay firmly in charge, because the buck stops with him (literally).

Since most owners have not received training in how to act as OIC, many of them are overwhelmed by the thought of taking command of the maintenance of their aircraft. “I don’t know anything about aircraft maintenance,” they sigh. “That’s way outside my comfort zone. Besides, isn’t that my mechanic’s job?”

Such owners often adopt the attitude that it’s their job to fly the aircraft and the mechanic’s job to maintain it. They leave the maintenance decisions up to the mechanics, and then get frustrated and angry when squawks don’t get fixed and maintenance expenses are higher than they expected.

But think about it: If you were building a house and you told your plumber or electrician or roofer “just do whatever it takes and send me the bill when it’s done,” do you think you’d be happy with the result?

No one in his right mind would do that, of course. If you were hiring an electrician to wire your house, you’d probably start by giving him a detailed list of exactly what you want him to do—what appliances and lighting fixtures you want installed in each room, where you want to locate switches, dimmers, convenience outlets, thermostats, telephone jacks, Ethernet connections, and so forth. You’d then expect the electrician to come back to you with a detailed written proposal, cost estimate, and completion schedule. After going over the proposal in detail with the electrician and making any necessary revisions, you’d sign the document and thereby enter into a binding agreement with the electrician for specific goods and services to be provided at a specific price and delivery date.

You’d do the same with the carpenter, roofer, drywall guy, paving contractor, and so forth.

Cars vs. airplanes

If you’ll permit me to mix my metaphors, when I take my car to the shop for service, the shop manager starts by interviewing me and taking notes on exactly what I want done—he asks me to describe any squawks I have to report, and he checks the odometer and explains any recommended preventive maintenance. Once we arrive at a meeting of the minds about what work needs to be done, the shop manager writes up a detailed work order with a specific cost estimate, and asks me to sign it and keep a copy. In essence, I now have a written contract with the shop for specific work to be done at a specific price.

The service manager doesn’t do this solely out of the goodness of his heart. He’s compelled to do so. In California where I live, state law provides that the auto repair shop is required to provide me with a written estimate in advance of doing any work, and may not exceed the agreed-to cost estimate by more than 10% unless I explicitly agree to the increase. If the shop doesn’t follow these rules, I can file a complaint with the State Bureau of Automotive Repairs and they’ll investigate and take appropriate action against the shop. Most states have similar laws.

Discrepancy List & Repair Estimate

Aircraft owners should insist on receiving a detailed written work statement and cost estimate like this one before authorizing any mechanic or shop to perform repairs or install replacement parts.

Unfortunately, there are no such laws requiring aircraft maintenance shops to deal with their customers on such a formalized and businesslike basis, even though the amounts involved are usually many times larger. Aircraft owners routinely turn their airplanes over to a mechanic or shop with no detailed understanding of what work will be done, what replacement parts will be installed, and what it’s all going to cost. All too often, the aircraft owner only finds this out when he picks up the aircraft and is presented with an invoice (at which point it’s way too late for him to influence the outcome).

It always amazes me to see aircraft owners do this. These are intelligent people, usually successful in business (which is what allows them to afford an airplane), who would never consider making any other sort of purchase of goods or services without first knowing exactly what they were buying and what it costs. Yet they routinely authorize aircraft maintenance without knowing either.

Often, the result is sticker shock and hard feelings between the owner and the shop. There’s no State Bureau of Aircraft Repair to protect aircraft owners from excessive charges or shoddy work. The FAA almost never gets involved in such commercial disputes. A few owners even wind up suing the maintenance shop, but generally the only beneficiaries of such litigation are the lawyers.

You can’t un-break an egg. You’ve got to prevent it from breaking in the first place.

Trust but verify

I hear from lots of these disgruntled aircraft owners who are angry at some mechanic or shop. When I ask why they didn’t insist on receiving a detailed work statement and cost estimate before authorizing the shop to work on their aircraft, I often receive a deer-in-the-headlights look, followed by some mumbling to the effect that “I’ve never had a problem with them before” or “you’ve got to be able to trust your A&P, don’t you?”

Sure you do…and you’ve got to be able to trust your electrician, plumber and auto mechanic, too. But that’s no excuse for not dealing with them on a businesslike basis. Purchasing aircraft maintenance services is a big-ticket business transaction, and should be dealt with as you would deal with any other big-ticket business transaction. The buyer and seller must have a clear mutual understanding of exactly what is being purchased and what it will cost, and that understanding must be reduced to writing.

In the final analysis, the most important factor that sets a maintenance-savvy aircraft owner apart from the rest of the pack is his attitude about maintenance. Savvy owners understand that they have primary responsibility for the maintenance of their aircraft, and that A&Ps, IAs and repair stations are contractors that they must manage. They deal with these maintenance professionals as they would deal with other contractors in other business dealings. They insist on having a written work statement and cost estimate before authorizing work to proceed. Then, like any good manager, they keep in close communication with the folks they’ve hired to make sure things are going as planned.

If your mechanic or shop resists working with you on such a businesslike basis, you probably need to take your business elsewhere.

Thinking, Fast and Slow

Wednesday, January 21st, 2015

Not long ago, I had a fascinating exchange with my friend and colleague Paul New. Paul is an A&P/IA and a truly extraordinary aircraft mechanic who was honored by the FAA as the National Aviation Maintenance Technician of the Year in 2007 (the year before I was so honored). But that’s where the historical similarity between me and Paul ends.

Paul New A&P/IA

Paul New, A&P/IA, owner of Tennessee Aircraft Services
and a truly extraordinary aircraft mechanic.

While I came to aircraft maintenance rather late in life, Paul has been immersed in it since childhood, helping his A&P/IA dad with numerous aircraft restoration projects well before he was tall enough to see over the glareshield without sitting on a phone book.

In 1981, Paul earned his degree in Avionics Technology from Southern Illinois University, and spent five years managing avionics shops for a commuter airline and an FBO. In 1986, he returned to Jackson, Tenn. to work with his dad in the aircraft restoration business once again, and in 1989 he purchased Tennessee Aircraft Services, Inc. from his dad and developed it into one of the premier Cessna Service Centers in the southeast US, performing both general maintenance and major structural repairs.

Over the years, Paul and I have formed an informal mutual admiration society, and frequently bounce problems, thoughts and ideas off one another. That’s exactly what was happening when we got into the conversation I’d like to share with you.

Cessna P210 engine problem

Paul emailed me about one of his customers who had recently encountered an engine problem shortly after takeoff on a recurrent training flight (with a CFI in the right seat). The owner/pilot told Paul that at about 400’ AGL, he noted a serious overboost, five inches over MAP red-line, and throttled back to bring the MAP back to red-line. At that point, according to the pilot, the engine started running very rough. The pilot elected to put the airplane down on the crossing runway, landed long and hot with a 17-knot tailwind, and took out the chain link fence at the far end of the runway. Paul was on his way to the scene of the incident to ferry the aircraft back to his shop for repairs.

Upon hearing his customer’s tale of woe, Paul’s first thought was that the pilot may have turned on the electric boost pump for takeoff, something you’re not supposed to do in the P210. According to Paul, “Leaving on the boost pump is a common mistake in Cessna 210s, particularly with pilots who are used to flying Lycoming-powered airplanes where turning on the boost pump for takeoff is SOP.”

Show me the data!

Paul arranged for his customer to dump the data from the P210’s JPI EDM-830 digital engine monitor data and to upload it to the website. Paul asked whether I’d be willing to take a look at it and give him my impressions, and I told him I’d be happy to do that.

P210 Engine Monitor Data

The engine monitor data told a different story than the pilot did.
Which would you believe?

When I looked at the engine monitor data, it seemed to tell a very different story than the one that the pilot had related Paul. I couldn’t see any evidence that the pilot flooded the engine by using the electric boost pump; the fuel flow data looked normal. Nor could I see any evidence that the pilot throttled back the engine (as he told Paul he’d done), because throttling back would have reduced fuel flow and the engine monitor recorded no reduction in fuel flow. What the data indicated was simply that the wastegate stuck closed on takeoff (causing the overboost) and then subsequently unstuck, reducing MAP to what it was supposed to be without any pilot input.

I also observed that while five of the six CHTs were rising as expected after takeoff power was applied, the CHT for cylinder #3 was falling, suggesting that cylinder #3 wasn’t making full power. If one cylinder wasn’t making full power, that would certainly account for the engine running rough. My diagnosis was that something went wrong with cylinder #3 after takeoff—maybe a clogged fuel nozzle, maybe a stuck valve—that caused the engine to run rough and scared the pilot into making a hasty and poorly executed downwind landing.

In reporting this to Paul, I added that “when confronted with significant dissonance between what a pilot reports and what an engine monitor reports, I’m inclined to believe the engine monitor.”

Do mechanics know too much?

Paul’s reply intrigued me:

Mike, thanks for the analysis. I agree with your diagnosis. But what I find most telling is the difference between my “mechanic’s analysis” and your “analyst’s analysis.” At the end of the day, I think like a career mechanic with decades of history crammed into my head, and my experience as a mechanic prejudices my view. Because the pilot’s account of events made me think of many occasions when Lycoming pilots get into a Continental airplane and turn on the electric fuel pump for takeoff, I was already spring-loaded to look for information to support this hypothesis.

My takeaway from this is that I—and I believe career mechanics in general—are  the wrong people to analyze engine data. Career mechanics carry too much mental baggage to be effective as analyst. What I see mechanics not doing well is “connecting the dots” to analyze an unusual event. It also occurs to me that we mechanics might do better if we looked at the engine monitor data first before we talk to the pilot. I think that would help us to evaluate the data more objectively.

Of course, I’m also a mechanic, but I don’t consider myself a “career mechanic” like Paul. I haven’t been working on airplanes since before puberty the way Paul has, and I’ve never made my living swinging wrenches the way Paul does. I don’t have those decades of real-world experiences crammed into my brain, so I tend to analyze things more “from first principles” while career mechanics like Paul tend to analyze them through “pattern matching” against the historical library in their noggins.

Thinking, fast and slow

Daniel Kahneman's book "Thinking, Fast and Slow"

Nobel laureate Daniel Kahneman’s book discusses human “two-system thinking” and explains its pitfalls.

In his 2011 book Thinking, Fast and Slow, economist and Nobel laureate Daniel Kahneman postulates that the human brain operates in two fundamentally different modes:

  • System 1 thinking:Operates automatically and quickly with little or no effort. It is fast, intuitive, emotional, and subsconscious.
  • System 2 thinking:Operates deliberatively and requires conscious effort. It is slow, rational, logical and calculating.

A student pilot relies on controlled System 2 thinking, requiring focused concentration on performing a sequence of operations that require considerable mental effort and are easily disrupted by distractions. In contrast, an experienced pilot, relying on automatic System 1 thinking, can carry out the same tasks efficiently while engaged in other activities (such as talking to ATC or calming a nervous passenger). Of course, the pilot can always switch to more conscious, focused and deliberative System 2 processing when he deems that to be necessary, such as when encountering challenging weather conditions or dealing with equipment failure.

Similarly, career A&P mechanics rely primarily on fast, automatic System 1 thinking. (Imagine what your maintenance invoice totals would be if they didn’t!) The more experience a mechanic has, the stronger his System 1 skills become. This kind of thinking serves the mechanic well most of the time, but it can break down when a challenging troubleshooting problem demands switching to slow, deliberative, thoughtful, logical System 2 thinking. Career mechanics often don’t have the time or training to flip that switch.

System 1 thinking is fast and easy and economical and even magical at times. The problem is that sometimes it yields the wrong answer. Consider this simple problem:

A bat and a ball together cost $5.50. If the bat costs $5 more than the ball, what does the ball cost?

Most people who look at that problem find that an answer—50 cents—pops into their mind immediately, effortlessly and without any conscious calculation. It’s intuitive, not reasoned.

It’s also wrong. The correct answer is 25 cents. To get the correct answer, most people have to consciously switch into “System 2 mode” and recognize that this is an algebra problem:

x + y = $5.50
x = y + $5.00
y = ???

Presented in that fashion, most people get the right answer. But such problems generally do not announce themselves as algebra problems. It takes training and skill to recognize when the mental switch needs to be flipped.

Do we need a new mechanic rating?

I attribute my skill as a troubleshooter largely to my training as a mathematician and my 30-year career as a professional software developer, both fields that deal with complex abstraction and absolutely demand strong System 2 thinking. At, most of our professional engine monitor data analysts are not A&P mechanics. One is a genomics researcher, two are aeronautical engineers, and yet another is an award-winning music composer—all fields that require a great deal of System 2 thinking. It’s rather rare to find career A&P mechanics with these sorts of backgrounds.

Other professions—notably medicine and education—recognize that diagnosis and therapy (or troubleshooting and repair, if you prefer) are dramatically different activities that require dramatically different skill sets. We don’t expect our neurosurgeons to interpret CT scans or analyze tissue samples or evaluate blood labs—we rely on radiologists, pathologists and hematologists for those things.

Similarly, I think perhaps it’s time that we stopped relying on career A&P mechanics—who are basically aircraft surgeons—to troubleshoot difficult problems, and started recognizing “mechanic-diagnostician” as a new aviation maintenance specialty. What do you think?

Are You Overinsured?

Wednesday, November 19th, 2014

Cessna 172RG gear-upI received a plaintive email from Bob, the owner of a Cessna 172RG Cutlass who found himself in an unexpected predicament. Seems he had an unfortunate gear-up landing. The airplane suffered only minimal damage, largely limited to minor belly damage and the outer four inches of the prop tips curled back. The engine had only about 100 hours SMOH at the time of the incident. Surely, all of this would be covered by insurance.

Unfortunately, Bob was about to learn a painful lesson about hull insurance:

“When I bought the $60,000 hull insurance policy, I didn’t read the fine print that said $60,000 wasn’t really available to fix the airplane in the event of a mishap. The actual amount available is the $60,000 policy limit minus the salvage value. The insurance company claims that they can get about $15,000 for the airplane for salvage, which only leaves me with about $45,000 to get the airplane fixed.

“Now here’s the rub: The repair shop has given a flat-rate bid of $41,000 plus tax to repair the airframe and do the requisite post-prop-strike engine teardown inspection. However, the bid explicitly excludes the cost of any necessary engine repairs beyond replacement of routine parts (rings, bearings, gaskets, etc.). The engine shop tells me that if the teardown inspection reveals that crankshaft and/or crankcase is damaged, the additional cost to repair could wind up being tens of thousands of dollars.

“Looking at the risk equation: In the best-case scenario, the repair cost is $41,000 plus tax and the insurance will cover it (just barely). In the worst-case scenario (if the case and crank are bad), I could wind up being out of pocket as much as $20,000, which would be painful. Alternatively, I could let the insurance company take the airplane, accept the $60,000 payout, and move on. But the airplane is only minimally damaged, and losing it under these circumstances would also be painful. What should I do?”

I discussed the various options with Bob. I pointed out that should he opt to have the aircraft repaired, even in the best-case scenario he would wind up with an aircraft that had substantial damage history and impaired resale value, and in the worst-case scenario he’d wind up seriously underwater (i.e., having a lot more invested that the aircraft was worth).

I suggested that setting aside his emotional attachment to the machine, the most logical course of action might well be to take the $60,000 and go shopping for another airplane. I also suggested that if Bob decides to repair the airplane, he might do better working with a smaller engine shop that specializes in prop-strike teardown inspections, and I offered him a couple of referrals.

Twin perils

Bob’s predicament reminded me of my recent phone conversation with Jack, a  friend who owns a Cessna T310R like mine. Jack flies it about 250 hours a year on business. Its a gorgeous machine, with RAM engines, Black Mac props, recent paint and interior, and a panel full of glass that leaves me drooling in envy.

In the course of a wide-ranging chat about flying and airplanes, our conversation turned to aircraft insurance. Jack and I compared notes on what insurance agencies we each used, who underwrote our policies, and what annual premiums we were paying. Jack’s premiums were about double what I was paying. As we pursued the matter further, Jack revealed that he was carrying nearly $300,000 worth of hull insurance on his airplane.

“Wow, that seems like an awful lot of hull coverage,” I said. “Have you looked at Controller or Aircraft Shopper Online or Trade-A-Plane recently? The piston twin market is really depressed right now. I bet the current fair market value of your airplane isn’t anywhere close to $300,000. I doubt it’s not more than $200,000.”

Jack admitted that he hadn’t been paying much attention to the market lately, and that it was certainly quite likely that his airplane wouldn’t fetch anywhere near $300,000 if he tried to sell it now. “But I figure that if I wrecked my airplane, I bet it would take at least $300,000 to buy a replacement and get it equipped and refurbished to match what I’m flying now.”

More coverage might be worse

Cessna 310 wreckage

If this were your airplane, would you prefer to repair it or just take the money and run?

I explained to my friend the perils of buying too much hull coverage.

“Jack, if you overinsure your hull for $300,000 coverage limits and then you have an accident that seriously trashes the airplane, you’ve got a real problem. Rather than declaring your airplane a total loss and handing you a check for $300,000, the insurance company might reimburse you for $175,000 in repairs. That could mean that you might be flying the airlines for 6 to 12 months while your aircraft is being extensively rebuilt, and in the end you’d wind up owning an aircraft with extensive damage history and impaired resale value.  This is probably not the outcome you want.”

At the same time, underinsuring the hull is also perilous. If Jack insured his hull for $130,000 and then made a gear-up landing with only minimal damage to the airframe, the insurance company could declare the aircraft a “constructive total loss” and hand Jack a check for $130,000. The company would then take possession of the Jack’s plane. Again, this is probably not the optimum result for Jack.

As a general rule of thumb, if you have an aircraft accident and the estimated cost to repair exceeds 75% to 85% of your hull insurance policy limit (sometimes called “stated value”), the company will declare the aircraft to be a total loss, take possession of the wreck, and pay you the coverage limit (less any deductibles). The insurance company will then try to obtain whatever value they can from the wreck, either by selling it to a salvage yard or by having it repaired and selling it on the market. On the other hand, if the estimated cost to repair is less than 75% to 85% of your policy limit, the insurance company will let you keep your aircraft and pay for the repairs. It’s the insurance company’s decision whether to “total the airplane” (not yours), and they make that decision whichever way they consider to be in their best interests (not yours).

The moral here is always to insure your aircraft for its current fair market value—not more nor less.

What’s it worth?

VREF aircraft valuation serviceIt’s prudent to reevaluate the fair market value of your airplane annually prior to renewing your aircraft insurance policy. Your hull coverage limits should be adjusted up or down each year as necessary to reflect the realities of the market.

For this purpose, many aircraft owners utilize AOPA’s online VREF Aircraft Valuation Service available free to AOPA members. Another method is to research the asking prices of comparable aircraft on major aircraft listing sites like ControllerAircraft Shopper Online, Trade-A-Plane, and Barnstormers. When checking comps, keep in mind that actual sale prices are usually 5% to 10% below the listed asking prices.

Liability limits

In addition to hull coverage, your aircraft policy insures us for liability in case you hurt someone or something while operating your aircraft. The liability coverage pays for a lawyer to defend you (or your estate) in the ensuing civil litigation, and if the plaintiffs prevail it will pay them damages up to the policy coverage limits.

The overwhelming majority of aircraft owners purchase $1 million of liability coverage. That’s because it’s generally accepted that anything less than $1 million is simply not sufficient to protect against air crash litigation, and more than $1 million can be hard and expensive to get in today’s aviation insurance market.

But not all $1 million liability policies are created equal. Some offer $1 million “combined single limit” coverage (colloquially known as “smooth”), while other policies include per-person or per-seat sublimits—often $100,000 per person or $100,000 per seat.

There’s a huge difference between “smooth” and sublimit coverage. If you crash and your sole passenger sustains severe injuries, a smooth policy will pay up to a million bucks to cover his damages, while a sublimits policy will pay only 10% of that amount.

Not worried because you never fly with anyone but family and close friends in your airplane? Think again. If you and your sibling or closest friend die in a crash, you can bet that your passenger’s widow or kids will hire the most aggressive personal injury lawyer she can find to sue your estate and make sure your widow or kids wind up with as little as possible.

Sublimit coverage might be okay if you always fly solo or if you have minimal assets, but most airplane owners don’t fall into that category. For most of us, smooth liability coverage is a must—and it’s becoming harder to find. Some underwriters won’t write anything but sublimit liability coverage, and others will renew smooth coverage for existing customers but won’t offer it to new applicants.

So next time your aircraft insurance comes up for renewal, take some time to think about what hull and liability coverage limits you want.

Carbon Monoxide, Silent Killer

Monday, October 20th, 2014

Danger, Carbon Monoxide
On January 17, 1997, a Piper Dakota departed Farmingdale, New York, on a planned two-hour VFR flight to Saranac Lake, New York. The pilot was experienced and instrument-rated; his 71-year-old mother, a low-time private pilot, occupied the right seat. Just over a half-hour into the flight, Boston Center got an emergency radio call from the mother, saying that the pilot (her son) had passed out.

The controller attempted a flight assist, and an Air National Guard helicopter joined up with the aircraft and participated in the talk-down attempt. Ultimately, however, the pilot’s mother also passed out.

The aircraft climbed into the clouds, apparently on autopilot, and continued to be tracked by ATC. About two hours into the flight, the airplane descended rapidly out of the clouds and crashed into the woods near Lake Winnipesaukee, New Hampshire. Both occupants died.

Toxicological tests revealed that the pilot’s blood had a CO saturation of 43% — sufficient to produce convulsions and coma—and his mother’s was 69%.

On December 6 that same year, a physician was piloting his Piper Comanche 400 from his hometown of Hoisington, Kansas, to Topeka when he fell asleep at the controls. The airplane continued on course under autopilot control for 250 miles until it ran a tank dry and (still on autopilot) glided miraculously to a soft wings-level crash-landingin a hay field near Cairo, Missouri.

The pilot was only slightly injured, and walked to a nearby farmhouse for help. Toxicology tests on a blood sample taken from the lucky doc hours later revealed CO saturation of 27%. It was almost certainly higher at the time of the crash.

Just a few days later, a new 1997 Cessna 182S was being ferried from the Cessna factory in Independence, Kansas, to a buyer in Germany when the ferry pilot felt ill and suspected carbon monoxide poisoning. She landed successfully and examination of the muffler revealed that it had been manufactured with defective welds. Subsequent pressure tests by Cessna of new Cessna 172 and 182 mufflers in inventory revealed that 20% of them had leaky welds. The FAA issued an emergency Airworthiness Directive (AD 98-02-05) requiring muffler replacement on some 300 new Cessna 172s and182s.

About 18 months later, the FAA issued AD 99-11-07 against brand new air-conditioned Mooney M20R Ovations when dangerous levels of CO were found in their cabins.

Sidebar: CO Primer

Click on image above for high-resolution printable version.

Not just in winter

A search of the NTSB accident database suggests that CO-related accidents and incidents occur far more frequently than most pilots believe. Counterintuitively, these aren’t confined to winter-time flying with the cabin heat on. Look at the months during which the following accidents and incidents occurred during the 15-year period from 1983 to 1997:

March 1983. The Piper PA-22-150 N1841P departed Tucumcari, N.M. After leveling at 9,600, the right front seat passenger became nauseous, vomited, and fell asleep. The pilot began feeling sleepy and passed out. A 15-year-old passenger in the back seat took control of the aircraft by reaching between the seats, but the aircraft hit a fence during the emergency landing. None of the four occupants were injured. Multiple exhaust cracks and leaks were found in the muffler. The NTSB determined the probable cause of the accident to be incapacitation of the PIC from carbon monoxide poisoning. [FTW83LA156]

February 1984. The pilot of Beech Musketeer N6141N with four aboard reported that he was unsure of his position. ATC identified the aircraft and issued radar vectors toward Ocean Isle, N.C. Subsequently, a female passenger radioed that the pilot was unconscious. The aircraft crashed in a steep nose-down attitude, killing all occupants. Toxicological tests of the four victims revealed caboxyhemoglobin levels of 24%, 22%, 35% and 44%. [ATL84FA090]

November 1988. The Cessna 185 N20752 bounced several times while landing at Deadhorse, Alaska. The pilot collapsed shortly after getting out of the airplane. Blood samples taken from the pilot three hours after landing contained 22.1% carboxyhemoglobin. The left engine muffler overboard tube was broken loose from the muffler where the two are welded. The NTSB determined probable cause to be physical impairment of the pilot-in-command due to carbon monoxide poisoning. [ANC89IA019]

July 1990. While on a local flight, the homebuilt Olsen Pursuit N23GG crashed about three-tenths of a mile short of Runway 4 at Fowler, Colo. No one witnessed the crash, but post-crash investigation indicated that there was no apparent forward movement of the aircraft after its initial impact. The aircraft burned, and both occupants died. Toxicology tests of the pilot and passenger were positive for carboxyhemoglobin. [DEN90DTE04]

August 1990. About fifteen minutes into the local night flight in Cessna 150 N741MF, the aircraft crashed into Lake Michigan about one mile from the shoreline near Holland, Mich. Autopsies were negative for drowning, but toxicological tests were positive for carboxyhemoglobin, with the pilot’s blood testing at 21%. [CHI90DEM08]

July 1991. The student pilot and a passenger (!) were on a pleasure flight in Champion 7AC N3006E owned by the pilot. The aircraft was seen to turn into a valley in an area of mountainous terrain, where it subsequently collided with the ground near Burns, Ore., killing both occupants. A toxicology exam of the pilot’s blood showed a saturation of 20% carboxyhemoglobin, sufficient to cause headache, confusion, dizziness and visual disturbance. [SEA91FA156]

October 1992. The pilot of Cessna 150 N6402S was in radio contact with the control tower at Mt. Gilead, Ohio, and in a descent from 5,000 feet to 2,000 feet in preparation for landing. Radar contact was lost, and the aircraft crashed into a wooded area, seriously injuring the pilot. Toxicological tests on the pilot’s blood were positive for carbon monoxide. Examination of the left muffler revealed three cracks and progressive deterioration. The NTSB found probable cause of the accident to be pilot incapacitation due to carbon monoxide poisoning. [NYC93LA031]

April 1994. Fifteen minutes after takeoff from Long Beach, Calif., the Cessna 182 N9124G began deviating from headings, altitudes and ATC instructions. The aircraft did several 360- and 180-degree turns. The pilot reported blurred vision, headaches, nausea, labored breathing, and difficulty staying awake. The aircraft ultimately crashed in a vineyard near Kerman, Calif., and the owner/pilot was seriously injured. Post-crash inspection revealed numerous small leaks in the exhaust system. The pilot tested positive for carbon monoxide even after 11 hours of oxygen therapy. [LAX94LA184]

October 1994. A student pilot returned to Chesterfield, Mo., from a solo cross-country flight in Cessna 150 N7XC, complaining of headache, nausea, and difficulty walking. The pilot was hospitalized, and medical tests revealed elevated CO which required five and a half hours breathing 100% oxygen to reduce to normal levels. Post-flight inspection revealed a crack in an improperly repaired muffler that had been installed 18 hours earlier. [CHI95IA030]

March 1996. The pilot of Piper Cherokee 140 N95394 stated that she and her passenger became incapacitated after takeoff from Pittsburg, Kan. The airplane impacted the terrain, but the occupants were uninjured. Both were hospitalized, and toxicological tests for carbon monoxide were positive. A subsequent examination found holes in the muffler. [CHI96LA101]

August 1996. A Mankovich Revenge racer N7037J was #2 in a four-airplane ferry formation of Formula V Class racing airplanes. The #3 pilot said that the #2 pilot’s flying was erratic during the flight. The airplane crashed near Jeffersonville, Ind., killing the pilot. The results of FAA toxicology tests of the pilot’s blood revealed a 41% saturation of carboxyhemoglobin; loss of consciousness is attained at approximately 30%. Examination of the wreckage revealed that the adhesive resin that bound the rubber stripping forming the firewall lower seal was missing. The NTSB determined probable cause of the accident to be pilot incapacitation due to carbon monoxide poisoning. [CHI96FA322]

January 1997. The fatal crash of Piper Dakota N8263Y near Lake Winnipesaukee, N.H. (described previously). [IAD97FA043]

December 1997. Non-fatal crash of Piper Comanche 400 N8452P flying from Hoisington to Topeka, Kansas (described previously). [CHI98LA055]

December 1997. A new Cessna 182S was being ferried from the factory in Independence, Kan., to a buyer in Germany when the ferry pilot felt ill and suspected carbon monoxide poisoning (described previously). [Priority Letter AD 98-02-05]

Overall, deaths from unintentional carbon monoxide poisoning have dropped sharply since the mid-1970s thanks mainly to lower CO emissions from automobiles with catalytic converters (most CO deaths are motor vehicle-related) and safer heating and cooking appliances. But CO-related airplane accidents and incidents haven’t followed this trend. The ADs issued against Independence-built Cessna 172s and 182s and Mooney Ovations demonstrates that even brand new airplanes aren’t immune.

CO Checklist

Click on image above for high-resolution printable version.

Close calls

In addition to these events in the NTSB accident database where CO poisoning was clearly implicated, there were almost certainly scores of accidents, incidents, and close calls where CO was probably a factor.

In January 1999, for example, a Cessna 206 operated by the U.S. Customs Service was on a night training mission when it inexplicably crashed into Biscayne Bay a few miles off the south Florida coast. The experienced pilot survived the crash, but had no recollection of what happened. The NTSB called it simple pilot error and never mentioned CO as a possible contributing factor. However, enough carboxyhemoglobin was found in the pilot’s blood that the Customs Service suspected that CO poisoning might have been involved.

The agency purchased sensitive industrial electronic CO detectors for every single-engine Cessna in its fleet, and discovered that many of the planes had CO-in-the-cockpit problems. On-board CO detectors and CO checks during maintenance inspections have been standard operating procedure for the Customs Service ever since.

How much CO is too much?

It depends on whom you ask.

EPA calls for a health hazard alert when the outdoor concentration of CO rises above 9 parts per million (ppm) for eight hours, or above 35ppm for one hour. OSHA originally established a maximum safe limit for exposure to CO in the workplace of 35 ppm, but later raised it to 50 ppm under pressure from industry.

The FAA requires that CO in the cabin not exceed 50 ppm during certification testing of new GA airplanes certified under FAR Part 23 (e.g. Cessna Corvallis, Cirrus SR22, Diamond DA-40). Legacy aircraft certified under older CAR 3 regs required no CO testing at all during certification.

Once certified, FAA requires no CO testing of individual aircraft by the factory, and no follow-up retesting during annual inspections. A March 2010 FAA SAIB (CE-10-19 R1) recommends checking CO levels with a hand-held electronic CO detector during ground runups at each annual and 100-hour inspection, but in my experience very few shops and mechanics do this.

UL-approved residential CO detectors are not permitted to alarm until the concentration rises to 70 ppm and stays there for four hours. (This was demanded by firefighters and utility companies to reduce the incidence of nuisance calls from homeowners.) Yet most fire departments require that firefighters put on their oxygen masks immediately when CO levels reach 25 ppm or higher.

It’s important to understand that low concentrations of CO are far more hazardous to pilots than to non-pilots. That’s because the effects of altitude hypoxia and CO poisoning are cumulative. For example, a COHb saturation of 10% (which is about what you’d get from chain-smoking cigarettes) would probably not be noticeable to someone on the ground. But at 10,000 feet, it could seriously degrade your night vision, judgment, and possibly cause a splitting headache.

After studying this hazard for many years and consulting with world-class aeromedical experts, I have come to the following conclusions:

  1. Every single-engine piston aircraft should carry a sensitive electronic CO detector.
  2. Any in-flight CO concentration above 10 ppm should be brought to the attention of an A&P for troubleshooting and resolution.
  3. Any in-flight CO concentration above 35 ppm should be grounds for going on supplemental oxygen (if available) and making a precautionary landing as soon as practicable.

Smokers are far more vulnerable to both altitude hypoxia and CO poisoning, since they’re already in a partially poisoned state when they first get into the aircraft. Because of COHb’s long half-life, you’d do well to abstain from smoking for 8 to 12 hours prior to flight.

Choosing a CO detector

Five CO detectors

Five CO detectors (left to right): chemical spot, UL-compliant residential (Kidde), non-UL-compliant (CO Experts 2015), industrial (BW Honeywell), TSO’d panel-mounted (CO Guardian 551).

Chemical spot detectors:Stay away from those ubiquitous el-cheapo adhesive-backed cardboard chemical spot detectors that are commonly sold by pilot shops and mail-order outfits for under trade names like “Dead Stop,” “Heads Up” and “Quantum Eye.” They have a very short useful life (about 30 days), and are extremely vulnerable to contamination from aromatic cleaners, solvents and other chemicals routinely used in aircraft maintenance.

These things often remain stuck on the instrument panel for years, providing a dangerous false sense of security. What’s worse, there’s no warning that the detector is outdated or has been contaminated—in some ways, that’s worse than not having a detector at all.

Even when fresh, chemical spot detectors are incapable of detecting low levels of CO. They’ll start turning color at 100ppm, but so slowly and subtly that you’ll never notice it. For all practical purposes, you’ll get no warning until concentrations rise to the 200 to 400 ppm range, by which time you’re likely to be too impaired to notice the color change.

Residential electronic detectors:Although battery-powered residential electronic detectors are vastly superior to those worthless chemical spots, most are designed to be compliant with Underwriter’s Laboratory specification UL-2034 (revised 1998). This spec requires that

(1)   The digital readout must not display any CO concentration less than 30 ppm.

(2)   The alarm will not sound until CO reaches 70 ppm and remains at or above that level for four hours.

(3)   Even at a concentration of 400 ppm, it may take as much as 15 minutes before the alarm sounds.

For aircraft use, you really want something much more sensitive and fast-acting. I like the non-UL-compliant CO Experts Model 2015 ($199 from It displays CO concentrations as low as 7 ppm and provides a loud audible alarm at concentrations above 25 ppm. It updates its display every 10 seconds (compared to once a minute for most residential detectors), which makes it quite useful as a “sniffer” for trying to figure out exactly where CO is entering the cabin.

Industrial electronic detectors:Industrial CO detectors cost between $400 and $1,000. A good choice for in-cockpit use is the BW Honeywell GasAlert Extreme CO  ($410 from This unit displays CO concentrations from 0 to 1,000 ppm on its digital display, has a very loud audible alarm with dual trigger levels (35 and 200 ppm).

Purpose-built aviation electronic detectors:Tucson-based CO Guardian LLC makes a family of TSO’d panel-mount electronic CO detectors specifically designed for cockpit use. These detectors detect and alarm at 50 ppm (after 10 minutes), or 70 ppm (after 5 minutes), and will alarm instantly if concentrations rise to 400 ppm. The digital display models ($599 and up) will show concentrations as low as 10 ppm. Available from Obviously, panel-mount detectors cannot be used as a sniffer to locate the source of a CO leak.

For more information…

There is an outstanding October 2009 research paper titled “Detection and Prevention of Carbon Monoxide Exposure in General Aviation Aircraft” authored by Wichita State University under sponsorship of the FAA Office of Research and Technology Development. The paper is 111 pages long, and discusses (among other things):

  • Characteristics of CO-related GA accidents
  • Evaluation of CO detectors, including specific makes and models
  • Placement of CO detectors in the cabin
  • Exhaust system maintenance and inspection

This research paper is available online at: