Posts Tagged ‘maintenance’

Assault on GA Down Under

Friday, October 9th, 2015
Nick McGlone

Nick McGlone with one of his Cessna 210s.

I just got off the phone with my good mate Nick McGlone from Sydney, Australia. For decades, Nick has operated Nautilus Air Services at Sydney’s Bankstown Airport. His firm operates a fleet of Cessna 210 Centurions whose primary mission is to haul sushi-grade fresh fish every day from Tasmania to Sydney. It’s roughly 650 miles from Sydney to Tasmania as the crow flies, about one-third of it overwater.

Now 70, Nick might just be the highest time Cessna 210 pilot in the world, with well over 30,000 hours in type. He’s also a master mechanic (they call them “LAMEs” down there) who maintains his airplanes in tip-top shape. He has to because he depends on them to be mission-ready every day.

After we exchanged a few pleasantries, Nick told me that his airplanes hadn’t flown for months and he was not confident that they would ever fly again. That stopped me dead in my tracks; he had my attention.

CASA’s War on Aging Aircraft

Nick explained to me that in recent years, Australia’s Civil Aircraft Safety Authority (CASA)—the Aussie counterpart to our FAA—had been implementing a series of draconian policies calculated to make it economically impossible for owners of legacy GA aircraft to keep them flying. He said that Bankstown Airport—traditionally the busiest GA airport in Australia—had become a virtual ghost town.

It seems that in 2014, the powers-that-be at CASA handed down a startling ruling that all operators of Australian-registered Cessnas would be required to comply with Cessna’s Supplemental Inspection Documents (SIDs). These SIDs set forth an extraordinarily extensive program of structural inspections that Cessna wants performed on a regular basis.

Some of the inspections in Cessna's SIDs are invasive, labor-intensive, and expensive.

Some of the inspections in Cessna’s SIDs are invasive, labor-intensive, and expensive.

Some of these inspections are relatively easy, but some are extraordinarily invasive and labor-intensive and costly. The SIDs specify a complex matrix of initial and repetitive compliance times for these various inspections. The most invasive and labor-intensive ones are to be done initially when the aircraft reaches 20 years old, and then repetitively every 3, 5, or 10 years thereafter. Of course, since all Cessna 300/400-series piston twins and all 200-series singles and the vast majority of 100-series singles are 30-60 years old, all of them are now past due for these inspections.

The FAA has ruled that compliance with these SIDs is strictly voluntary—NOT compulsory—for U.S.-registered aircraft that are maintained in accordance with the U.S. FARs. But CASA’s 2014 ruling was the exact opposite, and mandates that all Australian-registered aircraft MUST comply with the SIDs, whether the aircraft are in commercial service or private use.

Nick said that this is a catastrophe for Cessna owners in Australia (and in other nations like New Zealand and Germany and Spain who have also ruled that the SIDs are compulsory). Although the FAQ on CASA’s website says that compliance with the SIDs should cost about $20,000, Nick indicated that owners are finding that the actual cost of compliance is between $80,000 and $120,000 for Cessna singles, and close to $200,000 for Cessna twins. This is more than many of these aircraft are worth—or WERE worth before CASA made its ruling. Now, says Nick, the market value of these aircraft in Australia has dropped to near-zero, and many Australian owners are being forced to crate up their aircraft and ship them for sale in the U.S. (where compliance with the SIDs is not required).

Not Just Cessnas, Not Just SIDs

This catastrophe isn’t just limited to Cessnas, either. Now that Cessna’s parent company Textron Aviation owns Beechcraft, they’re feverishly working on developing a SID program for Bonanzas and Barons and other aging Beech airplanes. CASA has made it clear that the moment these Beech SIDs are published, CASA will mandate their compliance. There is even a rumor that Piper is working on a SID program for aging Piper airplanes.

All stainless steel control cables on Australian aircraft have to be replaced by the end of 2017.

All stainless steel control cables on Australian aircraft have to be replaced by the end of 2017.

And if that wasn’t bad enough, CASA has a few other tricks up its sleeve to make operation of aging GA aircraft unaffordable in the land down under. There’s a new Australian AD issued last February that requires that all primary flight control cables that use stainless steel end fittings (as almost all do) must be replaced with new cable assemblies by the end of 2017.  And another Australian AD that requires that all propellers undergo a complete disassembly inspection every six years and a major overhaul at the prop manufacturer’s specified TBO. None of these things are mandated by the FAA for U.S.-registered airplanes, nor is there a history of accidents or incidents in either country to justify such costly maintenance burdens on the owners of GA aircraft.

Nick told me that he is convinced that Textron and perhaps other manufacturers simply want their older aircraft to go away, and that they’ve been successful in enlisting CASA and various other national CAAs in helping them to achieve that goal. All of this is shrouded in the mantle of “aviation safety” despite the fact that there’s virtually zero history of accidents being caused by structural failure, control cable failure, or failure of high-time propellers. Nick could be right.

So next time you start griping about the high cost of personal flying, you might pause and thank your lucky stars that you’re based in the U.S. and not in the land down under. Compared to the rest of the world, we American aviators have it mighty good.

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?”

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?

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:

Backdoor Rule Making?

Wednesday, September 24th, 2014

On February 10, 2014, the Cessna Aircraft Company did something quite unprecedented in the history of piston GA: It published a revision to the service manual for cantilever-wing Cessna 210-series airplanes that added three new pages to the manual. Those three pages constituted a new section 2B to the manual, titled “Airworthiness Limitations”:

Cessna 210 Service Manual Section 2B

This section purports to impose “mandatory replacement times and inspection intervals for components and aircraft structures.” It states that the new section is “FAA-Approved” and that compliance is required by regulation.

Indeed, FARs 91.403(c) and 43.16 both state  that if a manufacturer’s maintenance manual contains an Airworthiness Limitations section (ALS), any inspection intervals and replacement times prescribed in that ALS are compulsory. FAR 91.403(c) speaks to aircraft owners:

§91.403(c) No person may operate an aircraft for which a manufacturer’s maintenance manual or instructions for continued airworthiness has been issued that contains an Airworthiness Limitations section unless the mandatory replacement times, inspection intervals, and related procedures specified in that section … have been complied with.

and FAR 43.16 speaks to mechanics:

§43.16 Each person performing an inspection or other maintenance specified in an Airworthiness Limitations section of a manufacturer’s maintenance manual or Instructions for Continued Airworthiness shall perform the inspection or other maintenance in accordance with that section…

Sounds pretty unequivocal, doesn’t it? If the maintenance manual contains an ALS, any mandatory inspection intervals and replacement times have the force of law.

The new ALS in the Cessna 210 maintenance manual mandates eddy current inspection of the wing main spar lower caps. For most 210s, an initial spar inspection is required at 8,000 hours time-in-service, with recurring inspections required every 2,000 hours thereafter. However, for 210s operated in a “severe environment” the inspections are required  at 3,500 hours and every 500 hours thereafter:

Cessna 210 inspection times

For P210s, the new ALS also imposes a life limit of 13,000 hours on the windshield, side and rear windows, and ice light lens.

What’s wrong with this picture?

To be fair, the eddy current inspection is not that big a deal.  An experienced technician can do it in a few hours. The most difficult part is that most service centers have neither the eddy current test eequipment nor a trained and certificated non-destructive testing (NDT) technician on staff. So most Cessna 210 owners will need to fly their airplane to a specialty shop  Since most airplanes will need to do this only once every 2,000 hours and since most of them fly less than 200 hours per year, one could hardly classify this recurrent eddy current inspection as Draconian. Similarly, not too many P210s are likely to reach the 13,000-hour life window life limit.

No, the issue isn’t the spar cap inspection or window life limits themselves—it’s the extraordinary method by which Cessna is attempting to make them compulsory.

Normally, if the manufacturer of an aircraft, engine or propeller wants to impose a mandatory inspection interval or a mandatory replacement or overhaul time on the owners of its aeronautical product, the manufacturer goes to the FAA and requests that an Airworthiness Directive (AD) be issued. If the FAA agrees and decides to issue an AD, it does so by means of a formal rule-making process prescribed by the federal Administrative Procedure Act (APA). Ultimately, the AD is published in the Federal Register and becomes an amendment to Part 39 of thee FARs. That’s what gives the AD its “teeth” and makes it compulsory for aircraft owners to comply with it.

§91.403(a) The owner or operator of an aircraft is primarily responsible for maintaining that aircraft in an airworthy condition, including compliance with part 39 of this chapter.

The APA governs the way that administrative agencies of the federal government (including the FAA) may propose and establish regulations. It has been called “a bill of rights” for Americans whose affairs are controlled or regulated by federal government agencies. The APA requires that before a federal agency can establish a new regulation, it must publish a notice of proposed rule making (NPRM) in the Federal Register, provide members of the public who would be impacted by the proposed regulation an opportunity to submit comments, and then take those comments seriously in making its final rule. The APA also establishes rights of appeal if a person affected by the regulation feels it is unjust or should be waived.

Because of the APA and other federal statutes, it is difficult for the FAA to issue ADs arbitrarily or capriciously. The agency first has to demonstrate that a bona fide unsafe condition exists, and that its frequency and severity of the safety risk rises to the level that makes rule making appropriate. It has to estimate the financial impact on affected owners. It has to provide a public comment period, give serious consideration to comments submitted, and respond to those comments formally when issuing its final rule.

As someone who has been heavily involved in numerous AD actions on behalf of various alphabet groups, I can tell you that the notice-and-comment provisions of the APA is extremely important, and that concerted efforts by aircraft owners and their representative industry organizations have often had great impact on the final outcome.

Through the back door?

That’s what makes Cessna’s action last February so insidious.

The addition of an Airworthiness Limitations section to the Cessna 210 maintenance manual was done without going through the rule making process. There was no NPRM and no comment period. Affected owners never had an opportunity to challenge the need for eddy current inspections of their wing spars. Cessna was never required to demonstrate that a genuine unsafe condition exists, nor weigh the cost impact against the safety benefit.Cessna 210 service manual By adding an ALS to the maintenance manual rather than ask the FAA to issue an AD, Cessna is attempting to bypass the APA-governed AD process and impose its will on aircraft owners through the back door.

Granted that the initial contents of the new ALS is not excessively burdensome. But if Cessna’s action is allowed to go unchallenged, it could set a terrible precedent. It would mean that any aircraft, engine or propeller manufacturer could retroactively impose its will on aircraft owners.

And if that happens, Katy bar the (back) door!

That’s why I’ve been working with my colleague Paul New—owner of Tennessee Aircraft Services, Inc. and honored by the FAA in 2007 as National Aviation Maintenance Technician of the Year—to challenge what Cessna is doing. On September 15th, Paul sent a letter that we jointly drafted to Mark  W. Bury (AGC-200), the FAA’s top regulations lawyer in its Office of General Counsel at FAA headquarters, asking him to issue a formal letter of interpretation as to whether compliance with the so-called mandatory inspection intervals set forth in section 2B of the Cessna 210 maintenance manual is actually required by regulation. We specifically ask Mr. Bury to rule on the question of whether retroactive enforcement of such a maintenance manual amendment by the FAA would constitute an APA violation.

The wheels of justice turn slowly at FAA Headquarters. We have been advised that AGC-200 has a four-month backlog of requests for letters of interpretation, so our request probably will not be looked at until the first quarter of 2015. But at least our request is in the queue. I am cautiously optimistic that AGC-200 will see things the way Paul and I see them, and will rule that a manufacturer’s publication of an ALS cannot be retroactively enforceable against aircraft owners unless the FAA issues an AD making it so.

Life on the Trailing Edge

Tuesday, August 26th, 2014

"Manifesto" is the first book by Mike Busch A&P/IA.

I just got back from EAA AirVenture in Oshkosh. It was a grueling week for me that included ten different Forums Plaza lectures, two “stump the IA” sessions at the AOPA seminar tent, and my first-ever AirVenture press conference. I’m still recovering.

AirVenture marked the release of my new book Manifesto, the first of what I expect to be a four- or five-volume series that anthologizes the most important of my aviation articles written over the past several decades. Manifesto is a short, pithy volume about maintenance philosophy. The next volume will be devoted to aircraft engines, and I’m hoping to have it out by the end of 2014.

One chapter of Manifesto is titled “How Mechanics Think” and addresses their extreme concerns about liability (both civil and regulatory), resulting in a compulsion to do everything exactly “by the book” and an aversion to trying anything new or different. It’s this aversion that is the subject of my blog post this month.

Tire Tactics

For the first decade after I purchased my Cessna 310 in 1987, I used Goodyear Flight Custom tires, which mechanics told me were “the gold standard” for GA aircraft tires. In 1998, I switched to Michelin Air tires because they were less expensive than the Flight Customs and were rated for the same weight and speed and reported to last just as long. I had just as good luck with the Michelins as I did with the Goodyears.

Then, in 2005, I decided to try Desser retreads after Aviation Consumer did a big competitive torture test of various tire brands (Goodyear, Michelin, McCreary, Condor), and found that Desser retreads fared even better than top-of-the-line Goodyear Flight Customs, even though they cost half as much.

Goodyear vs. Desser retreads

Are new tires (left) worth twice the price of retreads (right) that last longer?

I’ve used Desser retreads ever since, and Aviation Consumer was right: The darn things wear like iron. They’re dimensionally identical to new tires, so there’s never been any question about their fit in the wheel wells. Half the price, equal or better lifespan, perfect fit…what’s not to like? Could this be why most commercial aircraft operators and flight schools use retread tires, as do virtually all airlines?

In 2008, I started recommending Desser retreads for my company’s managed-maintenance clients. The reaction from shops and mechanics was astonishing. You’d have thought I’d just lit a stink bomb in church!

A number of shops flatly refused to install retreads, claiming they were taking this position “for liability reasons.” Others reacted with contempt and derision: “You’re serious about nickel-and-diming the maintenance by installing el-cheapo recaps on a half-million-dollar aircraft? Are you out of your mind?”

The fact that the biggest customers for retreaded aircraft tires are commercial operators, flight schools, and airlines didn’t seem to carry any sway with these mechanics. Nor the fact that Desser retreads beat Goodyear’s and Michelin’s top-of-the-line new tires in the Aviation Consumer torture test.

Silly me. I always considered saving money a good thing. To paraphrase the late Senator Everett Dirksen, “A hundred bucks here, a hundred bucks there, and pretty soon you’re talking real money.”

Six years later, all of my clients who followed my advice and opted for retreads and are very happy with their decision. Other clients demurred and sprung for the pricey Flight Custom IIIs, and they’re happy, too. I have learned not to push the issue. I still use Desser retreads on my airplane.

Spark Plug Wars

In 2006, I needed to replace the spark plugs on my airplane. My Cessna 310 has 24 spark plugs, so a full set of new plugs represents a non-trivial expense. While pricing out a set of Champion RHB32E massive-electrode plugs, I noticed that Autolite spark plugs were four bucks cheaper, a savings of $100 on 24 plugs. A hundred here, a hundred there….

Aviation spark plugsI’d used nothing but Champion plugs for the past 35 years, but as a world-class cheapskate I just couldn’t resist saving a hundred bucks, so I ordered the Autolites. When the new plugs arrived, I installed them and was very impressed. For one thing, the Autolite plugs are nickel-plated so they are much more corrosion-resistant than Champions (which are painted). For another, the Autolite threads start with a taper that makes them much easier to start in the cylinder spark plug boss. Subsequently, I learned that the Autolite plugs incorporated a fired-in sealed resistor assembly that solved the problem of high-resistance plugs that long plagued Champions.

Champion had dominated the aircraft spark plug market for as long as I could remember (and that’s a long time), but these Johnny-come-lately Autolites (first introduced in 2002) seemed like a better mousetrap. I’ve used Autolite plugs (which are now called “Tempest” after Unison sold the product line to Aero Accessories) ever since, and I love them. In 2008, I started recommending Autolite plugs to my managed-maintenance clients, and the blowback from their mechanics was truly breathtaking.

“My A&P was appalled that anyone would consider using Autolite plugs”, one owner told me. “Since he’s something of a curmudgeon, I asked my hangar neighbor (who’s an A&P) and was treated to a tirade about how he once tried a set of Autolites and they all died after 150 to 250 hours. I then wandered to another FBO on the field to take a straw poll of the two A&Ps on coffee break and was treated like a dummy who would sacrifice my airplane to save a few bucks.”

“I told my A&P this morning that I’d just installed Autolite plugs,” another owner said. “It was like throwing gasoline on a barbecue. I got out of there very quickly.”

Yet another owner received this inscrutable response from his A&P: “We like Champions, they’re better—but we use Autolites in our rental fleet and haven’t had any problems.” Translation: “If you’re paying for the plugs, we recommend the high-priced spread, but if we’re paying for them, well….”

I’ve never had an aircraft owner report any problems with the Autolite/Tempest plugs. Several manufacturers have issued service bulletins calling for Champion fine-wire plugs to be removed from service because they fail so often. Continental Motors now ships their new, rebuilt and overhauled engines strictly with Tempest plugs instead of Champions. Yet still I find that few A&Ps in the field stock anything but Champion plugs, and a few still refuse to install Tempests even when their customers specifically request them.

Where’s the Beef?

Why do so many A&Ps badmouth Desser retreads and Tempest plugs in the face of improved performance and cost-effectiveness? I’ve heard some owners suggest that it’s because there’s less mark-up on Desser tires than on Goodyears and on Tempest plugs than Champions. I’m not sure I buy that. In my experience, an A&P’s decisions are rarely motivated by greed, and are much more likely motivated by fear—specifically, fear of the unknown and fear of getting sued. Besides, a genuinely greedy A&P could find much more lucrative outlets for his greed than spark plugs and tires.

Tortoise and hare

Why are so many A&Ps late-adopters?

This resistance to trying new things—a “late-adopter” mentality—seems disturbingly common among A&Ps in my experience. It’s same psychology that causes some mechanics to discount the benefits of borescope inspections (often because they don’t own a borescope), spectrographic oil analysis, and digital engine analyzers (because they’re never learned to interpret the results), and to blame most cylinder problems on lean-of-peak operation (because they’ve never studied combustion theory and don’t realize that their Toyota runs LOP on the drive home from work).

Why are so many A&Ps skeptical of new-to-them products, methods and ideas? Why do so many choose to live life on the trailing edge of technology? Two reasons: lack of training and fear of being sued.

When I first earned my mechanic certificate (after having been a certificated pilot for 35 years), I was astonished to learn that the FAA has no regulatory requirements for an A&P to receive recurrent training of any kind. I found that shocking. If pilots have to go through recurrent training at least every two years, why doesn’t a similar requirement exist for the mechanics who maintain our airplanes?
In 2005, the FAA finally amended Part 145 to require mechanics who are employed by FAA certified repair stations to undergo initial and recurrent training. That’s certainly a step in the right direction. But the majority of A&Ps who work on our piston-powered aircraft are not employed by a certified repair station, so they still are not required to get any recurrent training. And the recurrent training that repair station mechanics receive often tends to reinforce the old way of doing things rather than teaching them about new ones. As a result, it’s not uncommon to find piston-GA mechanics whose knowledge is seriously stale and out-of-date.

Fear of being sued—liticaphobia—is a serious deterrent to mechanics trying something new. Lawsuits against shops and mechanics once were rare, but they have exploded over the last two decades for reasons I will discuss in a future blog post. The cost of defending such lawsuits can be ruinous for an individual mechanic or small business. Mechanics and shops have become very reluctant to try anything new or different, for fear it might come back to bite them in court.

I am certainly not suggesting that all piston-GA mechanics suffer from stale knowledge and a fear of trying new products and methods. The smartest and most talented A&Ps I know are information junkies and leading-edge thinkers. But many mechanics are incredibly resistant to change, very reluctant to adopt new technologies and methodologies, and their opinions often lack any basis in actual hard data. Owners are wise to seek expert second opinions rather than accepting their mechanics recommendations as gospel.

It can take real work for an aircraft owner to find a mechanic who is willing to consider new products and modern maintenance methods, but in my opinion it’s worth the effort.

What Makes an Engine Airworthy?

Wednesday, July 2nd, 2014

If we’re going to disregard manufacturer’s TBO (as I have advocated in earlier blog posts), how do we assess whether a piston aircraft engine continues to be airworthy and when it’s time to do an on-condition top or major overhaul? Compression tests and oil consumption are part of the story, but a much smaller part than most owners and mechanics think.

Bob Moseley

James Robert “Bob” Moseley (1948-2011)

My late friend Bob Moseley was far too humble to call himself a guru, but he knew as much about piston aircraft engines as anyone I’ve ever met. That’s not surprising because he overhauled Continental and Lycoming engines for four decades; there’s not much about these engines that he hadn’t seen, done, and learned.

From 1993 and 1998, “Mose” (as his friends called him) worked for Continental Motors as a field technical representative. He was an airframe and powerplant mechanic (A&P) with inspection authorization (IA) and a FAA-designated airworthiness representative (DAR). He was generous to a fault when it came to sharing his expertise. In that vein, he was a frequent presenter at annual IA renewal seminars.

Which Engine Is Airworthy?

During these seminars, Mose would often challenge a roomful of hundreds of A&P/IA mechanics with a hypothetical scenario that went something like this:

Four good-looking fellows, coincidentally all named Bob, are hanging out at the local Starbucks near the airport one morning, enjoying their usual cappuccinos and biscotti. Remarkably enough, all four Bobs own identical Bonanzas, all with Continental IO-550 engines. Even more remarkable, all four engines have identical calendar times and operating hours.

While sipping their overpriced coffees, the four Bobs start comparing notes. Bob One brags that his engine only uses one quart of oil between 50-hour oil changes, and his compressions are all 75/80 or better. Bob Two says his engine uses a quart every 18 hours, and his compressions are in the low 60s. Bob Three says his engine uses a quart every 8 hours and his compressions are in the high 50s. Bob Four says his compressions are in the low 50s and he adds a quart every 4 hours.

Who has the most airworthy engine? And why?

Compression/Oil Level

Don’t place too much emphasis on compression test readings as a measure of engine airworthiness. An engine can have low compression readings while continuing to run smoothly and reliably and make full power to TBO and beyond. Oil consumption is an even less important factor. As long as you don’t run out of oil before you run out of fuel, you’re fine.

This invariably provoked a vigorous discussion among the IAs. One faction typically thought that Bob One’s engine was best. Another usually opined that Bobs Two and Three had the best engines, and that the ultra-low oil consumption of Bob One’s engine was indicative of insufficient upper cylinder lubrication and a likely precursor to premature cylinder wear. All the IAs agreed Bob Four’s was worst.

Mose took the position that with nothing more than the given information about compression readings and oil consumption, he considered all four engines equally airworthy. While many people think that ultra-low oil consumption may correlate with accelerated cylinder wear, Continental’s research doesn’t bear this out, and Mose knew of some engines that went to TBO with very low oil consumption all the way to the end.

While the low compressions and high oil consumption of Bob Four’s engine might suggest impending cylinder problems, Mose said that in his experience engines that exhibit a drop in compression and increase in oil consumption after several hundred hours may still make TBO without cylinder replacement. “There’s a Twin Bonanza that I take care of, one of whose engines lost compression within the first 300 hours after overhaul,” Mose once told me. “The engine is now at 900 hours and the best cylinder measures around 48/80. But the powerplant is running smooth, making full rated power, no leaks, and showing all indications of being a happy engine. It has never had a cylinder off, and I see no reason it shouldn’t make TBO.”

Lesson of a Lawn Mower

To put these issues of compression and oil consumption in perspective, Mose liked to tell the story of an engine that was not from Continental or Lycoming but from Briggs & Stratton:

Snapper Lawnmower

If this one-cylinder engine can perform well while using a quart of oil an hour, surely an aircraft engine with 50 times the displacement can, too.

Years ago, I had a Snapper lawn mower with an 8 horsepower Briggs on it. I purchased it used, so I don’t know anything about its prior history. But it ran good, and I used and abused it for about four years, mowing three acres of very hilly, rough ground every summer.

The fifth year I owned this mower, the engine started using oil. By the end of the summer, it was using about 1/2 quart in two hours of mowing. If I wasn’t careful, I could run out of oil before I ran out of gas, because the sump only held about a quart when full. The engine still ran great, mowed like new, although it did smoke a little each time I started it.

The sixth year, things got progressively worse, just as you might expect. By the end of the summer, it was obvious that this engine was getting really tired. It still ran okay, would pull the hills, and would mow at the same speed if the grass wasn’t too tall. But it got to the point that it was using a quart of oil every hour, and was becoming quite difficult to start. The compression during start was so low (essentially nil) that sometimes I had to spray ether into the carb to get the engine to start. It also started leaking combustion gases around the head bolts, and would blow bubbles if I sprayed soapy water on the head while it was running. In fact, the mower became somewhat useful as a fogger for controlling mosquitoes. But it still made power and would only foul its spark plug a couple of times during the season when things got really bad.

Now keep in mind that this engine was rated at just 8 horsepower and had just one cylinder with displacement roughly the size of a coffee cup, was using one quart of oil per hour, and had zilch compression. Compare that to an IO-550 with six cylinders, each with a 5.25-inch bore. Do you suppose that oil consumption of one quart per hour or compression of 40/80 would have any measurable effect on an IO-550’s power output or reliability—in other words, its airworthiness? Not likely.

In fact, Continental Motors actually ran a dynamometer test on an IO-550 whose compression ring gaps had been filed oversize to intentionally reduce compression on all cylinders to 40/80, and it made full rated power.

Common Sense 101Let’s Use Common Sense

I really like Mose’s commonsense approach to aircraft engines. Whether we’re owners or mechanics (or both), we would do well to avoid getting preoccupied with arbitrary measurements like compression readings and oil consumption that have relatively little correlation with true airworthiness.

Instead, we should focus on the stuff that’s really important: Is the engine “making metal”? Are there any cracks in the cylinder heads or crankcase? Any exhaust leaks, fuel leaks, or serious oil leaks? Most importantly, does the engine seem to be running rough or falling short of making full rated power?

If the answer to all of those questions is no, then we can be reasonably sure that our engine is airworthy and we can fly behind it with well-deserved confidence.

On-Condition Maintenance

The smart way to deal with engine maintenance—including deciding when to overhaul—is to do it “on-condition” rather than on a fixed timetable. This means that we use all available condition-monitoring tools to monitor the engine’s health, and let the engine itself tell us when maintenance is required. This is how the airlines and military have been doing it for decades.

Digital borescope (Adrian Eichhorn)

Digital borescopes and digital engine monitors have revolutionized piston aircraft engine condition monitoring.

For our piston aircraft engines, we have a marvelous multiplicity of condition-monitoring tools at our disposal. They include:

  • Oil filter visual inspection
  • Oil filter scanning electron microscopy (SEM)
  • Spectrographic oil analysis programs (SOAP)
  • Digital engine monitor data analysis
  • Borescope inspection
  • Differential compression test
  • Visual crankcase inspection
  • Visual cylinder head inspection
  • Oil consumption trend analysis
  • Oil pressure trend analysis

If we use all these tools on an appropriately frequent basis and understand how to interpret the results, we can be confident that we know whether the engine is healthy or not—and if not, what kind of maintenance action is necessary to restore it to health.

The moment you abandon the TBO concept and decide to make your maintenance decisions on-condition, you take on an obligation to use these tools—all of them—and pay close attention to what they’re telling you. Unfortunately, many owners and mechanics don’t understand how to use these tools appropriately or to interpret the results properly.

When Is It Time to Overhaul?

It takes something pretty serious before it’s time to send the engine off to an engine shop for teardown—or to replace it with an exchange engine. Here’s a list of the sort of findings that would prompt me to recommend that “the time has come”:

Lycoming cam and lifter

Badly damaged cam lobe found during cylinder removal. “It’s time!”

  • An unacceptably large quantity of visible metal in the oil filter; unless the quantity is very large, we’ll often wait until we’ve seen metal in the filter for several shortened oil-change intervals.
  • A crankcase crack that exceeds acceptable limits, particularly if it’s leaking oil.
  • A serious oil leak (e.g., at the crankcase parting seam) that cannot be corrected without splitting the case.
  • An obviously unairworthy condition observed via direct visual inspection (e.g., a bad cam lobe observed during cylinder or lifter removal).
  • A prop strike, serious overspeed, or other similar event that clearly requires a teardown inspection in accordance with engine manufacturer’s guidance.

Avoid getting preoccupied with compression readings and oil consumption that have relatively little correlation with true airworthiness. Ignore published TBO (a thoroughly discredited concept), maintain your engine on-condition, make sure you use all the available condition-monitoring tools, make sure you know how to interpret the results (or consult with someone who does), and don’t overreact to a single bad oil report or a little metal in the filter.

Using this reliability-centered approach to engine maintenance, my Savvy team and I have helped hundreds of  aircraft owners obtain the maximum useful life from their engines, saving them a great deal of money, downtime and hassle. And we haven’t had one fall out of the sky yet.