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Author: Mike Busch (page 1 of 4)

Why change the oil?

Aeroshell W100 PlusContinental and Lycoming tell us that we must change the oil in our engines every 50 hours or 4-6 months, whichever comes first—and that’s if we have a full-flow oil filter installed. If we have only an oil screen, then the oil change interval goes down to 25 hours. Did you ever wonder why we need to change the oil so often?

It’s not because the oil breaks down in service and its lubricating qualities degrade. The fact is that conventional petroleum-based oils retain their lubricating properties for a very long time, and synthetic oils retain them nearly forever.

Consider, for example, that most automobile manufacturers now recommend a 7,500-mile oil-change interval for most cars and light trucks. That’s the equivalent of 150 to 250 hours of engine operation. In fact, oil analysis studies have shown that a synthetic automotive oil like Mobil 1 or Amsoil can go 18,000 miles without appreciable degradation, and that’s the equivalent of 400-600 hours.

Filth

No, the reason we change oil in our aircraft engines every 25 to 50 hours is not because it breaks down. It’s because it gets contaminated after 25 to 50 hours in an aircraft engine. In fact, it gets downright filthy and nasty.

DHMO

Dihydrogen monoxide (DHMO) is a highly corrosive chemical that is produced in copious quantities during combustion, and can cause great harm to costly engine components when it blows by the piston rings and contaminates the engine oil. You may be more familiar with DHMO’s common chemical formula: H2O.

Compared with automotive engines, our piston aircraft engines permit a far greater quantity of combustion byproducts—notably carbon, sulfur, oxides of nitrogen, raw fuel, partially burned fuel, plus massive quantities of the corrosive solvent dihydrogen monoxide or DHMO (see graphic)—to leak past the piston rings and contaminate the crankcase. This yucky stuff is collectively referred to as “blow-by” and it’s quite corrosive and harmful when it builds up in the oil and comes in contact with expensive bottom-end engine parts like crankshafts and camshafts and lifters and gears.

To make matters worse, avgas is heavily laced with the octane improver tetraethyl lead (TEL), which also does nasty things when it blows by the rings and gets into the crankcase. (If you’re as old as I am, you may recall that back before mogas was unleaded, the recommended oil-change interval was 3,000 miles instead of 7,500 miles.)

So one of the most important reasons that we need to change the oil regularly in our Continentals and Lycomings is to get rid of these blow-by contaminants before they build up to levels that are harmful to the engine’s health.

Acid

Another reason we need to change the oil regularly—arguably even more important than disposing of contaminants—is to replenish the oil’s additive package, particularly its acid neutralizers. When sulfur and oxides of nitrogen mix with DHMO, they form sulfuric acid and nitric acid. If you remember these dangerous corrosives from your high school chemistry class, then you’ll certainly appreciate why you definitely don’t want them attacking your expensive engine parts.

OIl analysisTo prevent such acid attack, aviation oils are blended with acid neutralizer additives. These are alkaline substances that neutralize these acids, much as we might use baking soda to neutralize battery acid. These acid neutralizers are consumed by the process of neutralizing acids, so it’s imperative that we replenish them before they get used up to an extent that might jeopardize our hardware. Of course, the way we replenish them is to change the oil.

How can we tell when the acid neutralizers in the oil have been used up? It turns out that there’s a laboratory test that measures the level of unneutralized acid remaining in the oil. This is known as the “total acid number” or “TAN” test. Some oil analysis firms can perform this test on your oil samples. However, it’s not routinely done as part of the normal oil analysis report, so you need to specially request a TAN test when you send in your oil sample (and be prepared to pay extra for it).

Intervals

Tach w/hourmeterMost owners don’t bother with the hassle and expense of TAN testing, and simply change their oil at a conservative interval that’s guaranteed to get the junk out and fresh additives in before anything untoward is likely to occur.

On my own airplane, what I do (and generally recommend to my clients) is to change the oil and filter every 50 hours or 4 calendar months, whichever comes first. This means that operators who fly at least 150 hours a year can go 50 hours between oil changes, but operators who fly less will use a proportionately reduced oil-change interval.

This recommendation assumes that the aircraft has a full-flow (spin-on) oil filter installed, that it operates primarily from paved runways, and that it has decent compressions and relatively low blow-by past the rings. Engines that have only an oil screen (no filter) should have the oil changed every 25 hours. Engines that operate in dirty or dusty conditions and ones that have high oil consumption due to high blow-by should have more frequent oil changes.

My friend Ed Kollin—lubrication engineering wizard who used to head Exxon’s lubrication lab and who developed ASL CamGuard—is even more conservative. He preaches that oil should be changed no less frequently than every 30 hours, and frowns when I suggest that it’s okay to go to 50 if you fly a lot.

Insolubles

InsolublesAnother important indication of oil condition can be found in standard oil analysis report provided by some labs—notably the one I prefer, Blackstone Laboratories in Ft. Wayne, Indiana—is the “insolubles” test. This test is performed by placing the oil sample in a centrifuge to separate out all solids and liquids in the sample that are not oil-soluble.

Virgin oil normally contains no insolubles. The insolubles found in drained engine oil come from three sources: (1) oxidized oil that breaks down due to excessive heat; (2) contaminants from blow-by of combustion byproducts; and (3) particulate contamination caused by poor oil filtration. If your oil analysis report reveals above-normal insolubles, it might be indicative of an engine problem—high oil temperature, excessive blow-by, inadequate filtration—and almost certainly means you should be changing your oil more frequently.

By the way, did I mention that I’m a huge fan of laboratory oil analysis? I use it religiously, recommend it strongly to all piston aircraft owners, and believe that it’s one of the most important tools we have—along with oil filter inspection and borescope inspection—for monitoring the condition of our engines and determining when maintenance is necessary.

Mike Busch is arguably the best-known A&P/IA in general aviation, honored by the FAA in 2008 as National Aviation Maintenance Technician of the Year. Mike is a 7,500-plus hour pilot and CFI, an aircraft owner for 45 years, a prolific aviation author, co-founder of AVweb, and presently heads a team of world-class GA maintenance experts at Savvy Aviation. Mike’s book Manifesto: A Revolutionary Approach to General Aviation Maintenance is available from Amazon.com in paperback and Kindle versions.

Temperamental Ignition

A funny thing happened to me on a coast-to-coast trip from California to the East Coast in my Cessna 310. I was on a business trip that would take me from my home base in Santa Maria, California, to Frederick, Maryland, then to Atlanta, Georgia, and then home again.

I first became aware of the problem as I was climbing out of Santa Maria on the very first leg of what I expected to be a 30-hour round-trip. I had reduced to my usual 75% cruise-climb power, was climbing at my usual 130 KIAS cruise-climb airspeed, with the usual 110 pounds/hour fuel flow on each engine. This was all standard routine that I’d performed hundreds of times before.

The engines felt smooth. The airplane was climbing nicely at about 1,000 FPM despite being loaded right at max gross.  The air was smooth. My yoke-mounted SeriusXM satellite weather display indicated no significant weather all the way to Tulsa, Oklahoma, where I planned to make an overnight stop before continuing on to Frederick. The SeriusXM audio was tuned to the classical music channel, piping one of my favorite Bach Brandenburg Concertos into my stereo ANR headset. All seemed right with the world.

My reverie was interrupted by a flashing amber annunciator light that told me my digital engine monitor was trying to get my attention. Sure enough, when I looked over at the instrument on the right side of the panel, its display was flashing a high turbine inlet temperature (TIT) alarm on the left engine, and displaying the TIT as 1620°F. I knew from experience that normal TIT in this configuration is around 1570°F and I’d programmed the engine monitor to alarm any time the TIT exceeded 1600°F.

JPI EDM 760 engine monitor

On climbout, the left engine showed excessive TIT and excessive EGT on the #5 cylinder. However, #5 CHT was normal. This suggested that one spark plug might not be firing in the #5 cylinder. An in-flight mag check confirmed that indeed the bottom plug was not firing.

In-flight troubleshooting

Looking carefully at the engine monitor’s digital readouts, I noticed that the EGT on the left engine’s #5 cylinder was noticeably higher than the other cylinders, and definitely higher than what I was used to seeing. The high #5 EGT suggested to me one of two possible problems: (1) a partially clogged #5 injector; or (2) a #5 spark plug that wasn’t firing.

If a clogged injector was causing cylinder #5 to run too lean, I would have expected that cylinder also to have elevated CHT while operating ROP during climb. However, the engine monitor did not indicate that the #5 CHT was elevated; if anything, it seemed to be a bit lower than usual.

That suggested to me that a non-firing spark plug was the most likely cause of the elevated #5 EGT. To confirm this theory, I performed an in-flight mag check. When I shut off the righthand magneto switch for the left engine, the left engine started running quite rough and the #5 EGT bar on the display dropped out of sight.

Bingo!

My problem was definitely a non-firing spark plug in the #5 cylinder.

Which plug wasn’t firing? Because the cylinder went cold when I shut off the right magneto, the non-firing plug had to be the one connected to the left magneto. On my engines (as with most big-bore TCM engines), each magneto fires the top plugs on its side of the engine and the bottom plugs on the opposite side of the engine. Since cylinder #5 is in the right bank of cylinders, its top plug is fired by the right mag and its bottom plug is fired by the left mag. Therefore, I reasoned, my non-firing spark plug had to be the bottom plug on cylinder #5.

(Bottom plugs tend to misfire much more often than top plugs, because the bottom ones are so vulnerable to oil-fouling and contamination with debris.)

That’s odd, I thought. I had done a thorough runup prior to takeoff, including the usual preflight mag check at 1700 RPM. All 24 spark plugs appeared to be working just fine. Why would one decide to quit working now? Definitely odd.

I leveled off at my cruising altitude of 13,000 feet and did the “big mixture pull” to transition to LOP. The engine monitor continued to show elevated DIFF on the left engine, and elevated #5 EGT. During the next couple of hours, I repeated the in-flight mag check a couple of more times and got exactly the same result: The bottom plug on cylinder #5 was definitely not firing.

Sometimes fouled plugs clear themselves spontaneously. But not this time. Darn!

Not to worry, that’s why I always carry a couple of spare spark plugs in the emergency toolkit I keep in my left wing locker, together with the necessary tools to change out a plug on the ramp if necessary. So I knew what I had to do.

Spark plug transplant

I landed at my first planned refueling stop, Saint Johns, Arizona. KSJN is a frequent fuel stop for me going eastbound because it consistently has among the lowest 100LL prices west of the Mississippi. Also, KSJN has a field elevation of 5,736 feet MSL, which shortens the descent for landing and the subsequent climb back to altitude. All in all, it’s one of my favorite places to refuel.

After topping off the tanks, I retrieved my emergency toolkit and proceeded to remove the bottom spark plug from cylinder #5 of the left engine.

The plug had been in service for about 100 hours, and it looked okay to me. But since it clearly wasn’t firing, I decided to swap it out anyway. I installed a brand new spark plug in the bottom plug hole of left engine cylinder #5, torqued it to 360 in.-lbs. using the torque wrench I carry in my emergency toolkit, and reattached the ignition lead.

After closing up the left engine nacelle and stashing my emergency toolkit back in the wing locker, I fired up and taxied out for departure. At the runup area, I performed an extra diligent runup and mag check to verify that all plugs were firing properly—they were. I then took off and turned eastbound toward Tulsa.

Climbing out of KSJN, I tuned the SeriusXM audio to the ‘60s oldies channel and was just getting into the groove when it happened again: The amber light started flashing and the engine monitor started complaining about high TIT on the left engine. A quick cycle of the instrument and a quick in-flight mag check confirmed that the bottom plug on #5 was once again not firing. Yes, the very same brand new spark plug that I’d just installed!

Bummer!

Plug transplant, part deux

I continued on to Tulsa, taxied to the FBO, and broke out my emergency toolkit once again. This time, I removed the newly-installed plug and installed my one remaining spare. I wasn’t sure it would solve my problem, but figured it was worth a shot.

The next day, climbing eastbound out of Tulsa, I actively monitored the engines looking for signs of trouble. Everything seemed to be working fine. After leveling off in cruise and switching to LOP, I tried another in-flight mag check. The left engine continued to run smoothly on each magneto  individually, and the engine monitor confirmed that everything was operating normally now.

Whoopie!

I flew nonstop to Frederick at FL210 (to stay above a bunch of rather nasty frontal weather). High-altitude LOP operation is pretty demanding on the ignition system, but the engines didn’t miss a beat and another in-flight mag check at altitude confirmed that all was well.

After completing my business in Frederick, I flew to Charlotte, North Carolina to spend a few days with my in-laws who live there, then proceeded on to Atlanta for another business meeting. After that, I headed home to the west coast with stops in Memphis and Denver. The engines continued to run perfectly, and I pretty much forgot about the earlier ignition problem.

It’s baaaack!

After returning home to Santa Maria and resting up a bit, I decided it was time to do some preventive maintenance on the airplane. I changed the oil, sent oil samples to the lab for analysis, replaced the oil filters, and cut open the old filters for inspection. (No metal.)

Since the spark plugs had over 100 hours on them, I pulled them and sent them to Aircraft Spark Plug Service in Van Nuys for cleaning, gapping, and bomb testing. All of my cleaned/gapped spark plugs passed the bomb test with flying colors and came back a week later, whereupon I reinstalled them in the engines.

After closing up the engine nacelles, I took the airplane out for a post-maintenance test flight. A thorough pre-flight runup indicated that everything was working fine. But the test flight once again revealed elevated DIFF and elevated #5 EGT on the left engine, and an in-flight mag check showed the bottom #5 spark plug was once again not firing. Arggghhh!!!

It was finally starting to dawn on me that the ignition problem must be something other than a bad spark plug. It had to be either a problem with the magneto itself or a problem with the ignition harness.

I tried replacing the insulator (“cigarette”) and contact spring on the bottom #5 ignition lead, but another test flight showed that this did not solve the problem. I pulled the left mag and opened it up, but couldn’t find anything wrong. The distributor cap was clean inside, the contact springs looked good, the point gap was correct and the internal and external mag timing was spot-on.

Harness transplant

By elimination, that left the ignition harness. I examined the #5 bottom ignition lead and couldn’t spot any visual anomalies. But since I was running out of ideas, and since a brand new full harness (for both mags) cost less than $500.00, I decided to order one and install it. Even though the existing harness looked fine, it did have nearly 2,000 hours on it, so presumably it was fully depreciated.

Ignition Harness

A new full harness (for both magnetos) costs only about $500. (A harness for just one magneto is called a “half harness.”) Figure on four hours of labor to install. I prefer the Slick-brand harnesses (shown above) because of their superior construction and flexibility.

There are a variety of ignition harnesses that are PMA approved for my engines, including Champion, Kelly, Skytronics, Continental, and Slick. I have always preferred the Slick harnesses because of their superior construction and flexibility, so I ordered a new Slick M1740 harness to mate with my Continental/Bendix S-1200 magnetos.

Removing the old harness and installing the new one was more time-consuming than I expected. Doing the job correctly involves considerable Adel clamping, grommeting, and tie-wrapping to ensure that the ignition leads cannot vibrate or chafe on anything and have no tight bends. It took me about six hours to complete the job, including retiming both mags.

I am, of course, the world’s slowest mechanic. I imagine a professional A&P could do it in three or four hours.

Finally, it was time to do yet another post-maintenance test flight. This time, I was overjoyed to find that everything was perfect. The engine monitor readings were just as they should be, and a high-power in-flight mag check showed all systems go. Success at last!

Lessons learned

I learned some important lessons as a result of this experience. One is that the usual pre-flight mag check is a laughably inadequate test of ignition system performance. While trying to track down my problem with a non-firing #5 bottom plug, the ignition system repeatedly showed no problems whatsoever during the pre-flight mag check, only to fail immediately and repeatably as soon as the aircraft was in flight.

Clearly, the pre-flight mag check is not a very demanding test of the ignition system, and won’t detect anything but the grossest ignition anomalies. An in-flight mag check is a far more demanding and revealing test. The most demanding ignition system test is a high-power in-flight mag check with the engine leaned aggressively (preferably LOP).

Many pilots have never done an in-flight mag check, and many are afraid to perform one. I’ve even known some experienced A&P mechanics that discourage pilots from shutting off a magneto in flight. Obviously, I don’t agree with that advice. In fact, in the wake of my experience, I now make a point of performing an in-flight mag check on almost every flight, and I heartily recommend that you consider adopting the same practice.

Another lesson I learned here is the tremendous diagnostic value of a modern digital probe-per-cylinder engine monitor. If it hadn’t been for my JPI EDM 760, I’d never have known that my #5 bottom plug was not firing. It’s quite possible that this situation could have gone on for months and hundreds of hours without being detected. Once again, my engine monitor proved that it is worth its weight in gold.

Finally, I learned that ignition harnesses have a finite useful life. They may look perfect upon visual inspection, yet develop internal electrical leaks that seriously compromise ignition system performance. Since a new harness is relatively inexpensive (at least as aircraft parts go), it probably wouldn’t be a bad idea to replace the ignition harness every 1,000 hours or so just on general principles. In fact, I decided to order another new harness and installed it on my right engine, so now both engines have new harnesses.

Mike Busch is arguably the best-known A&P/IA in general aviation, honored by the FAA in 2008 as National Aviation Maintenance Technician of the Year. Mike is a 7,500-plus hour pilot and CFI, an aircraft owner for 45 years, a prolific aviation author, co-founder of AVweb, and presently heads a team of world-class GA maintenance experts at Savvy Aviation. Mike’s book Manifesto: A Revolutionary Approach to General Aviation Maintenance is available from Amazon.com in paperback and Kindle versions.

Scope That Jug!

continental-cylinder-removalIn 2002, I did something unfortunate: pulled a perfectly good cylinder off of one of the engines of my Cessna 310. If I had it to do over again, I wouldn’t have touched the cylinder. But at the time, I thought I was doing the right thing.

It was the usual story. I had just downed the airplane for its annual inspection, and the first items on my checklist were performing a hot compression check, draining the oil, sending oil samples to the lab, and cutting open the oil filters for inspection.

All the cylinders had compressions in the low- to mid-70s. All but one, that is. That one measured about 60/80 with air leaking past the exhaust valve.

At the time, the engine manufacturer’s guidance on compression tests was Continental Motors service bulletin M84-15, which instructed mechanics that a jug could leak considerably past the rings and still be considered perfectly airworthy. However, any leakage at all past the valves was considered unacceptable, according to TCM, and required the cylinder to come off for repair or replacement.

So off it came.

Pulling a cylinder is a real PITA. I spent two hours removing cooling baffles and the exhaust and induction plumbing. It took me another hour to remove the rocker cover, rocker shafts, rocker arms, pushrods and pushrod housings. Finally, I used a cylinder base wrenches and a big breaker bar to coerce the eight cylinder base nuts loose. About four hours into the project, I held the offending jug in my arms and carried it over to my workbench to survey the damage.

I inspected the cylinder closely, with special attention on the exhaust valve. Surprisingly, I couldn’t see anything wrong. The valve looked normal, as did the rest of the cylinder. Yet it must have been bad, I thought, because it had clearly been leaking air past the exhaust valve.

I sent the cylinder out for re-valving and honing, installed new rings on the piston, then spent another four hours reinstalling them on the engine and replacing the exhaust, intake and baffles.

Like I said, it was a PITA. It cost me more than $500 plus a full day of sweat equity. (Had I not been doing the grunt work myself, the tab would have been at least $1,500.)

Continental pulls a switcheroo

That episode turned out to be a classic case of bad timing. Had my annual inspection come a few months later, that cylinder would never have been yanked. That’s because not long after my jug came off, Continental radically changed its guidance to mechanics regarding cylinder inspection.

On March 28, 2003, the wizards in Mobile issued service bulletin SB03-3 titled “Differential Pressure Test and Borescope Inspection Procedures for Cylinders.”  This 14-page document is arguably the best guidance ever provided to mechanics on the subject of when a cylinder should be pulled. (SB03-3 was recently incorporated into Continental Motors Standard Practice Maintenance Manual X-0, and is no longer a service bulletin.)

Continental’s guidance in SB03-3 differed from its predecessor M84-15 in two crucial respects. First, it reverses Continental’s previous position that even small amounts of leakage past the valves during a compression check is unacceptable and grounds for pulling the cylinder. Many experienced A&Ps considered the “zero leakage past the valves” standard as being unrealistic and after 19 years Continental finally agreed with that assessment.

The other difference is arguably even more important: For the first time, Continental directed mechanics to perform a borescope inspection of the cylinders at each annual inspection, 100-hour inspection, and any other time a compression check is done. Continental’s language about this is quite emphatic: “Continental Motors REQUIRES a cylinder borescope inspection be accomplished in conjunction with the differential pressure test.”

This was huge.

Although SB03-3 officially applies only to Continental engines, the guidance it offers makes good sense for Lycomings, too.

Borescope choices

Lennox Autoscope

Lennox Autoscope

At the time in 2003, borescopes were expensive and exotic devices whose use was pretty much limited to turbine engine inspections. Relatively few piston GA maintenance shops and A&P mechanics owned a borescope, and even fewer had a clue how to use one or what to look for. In SB03-3, Continental specifically recommended a particular make and model of borescope: the “Autoscope” from Lenox Instrument Company in Trevose, Pa. This was a simple, low-cost rigid borescope developed in the mid-1980s for use by auto mechanics, and cost about $1,000. The Lennox Autoscope had excellent optics and provides a remarkably clear view of what’s going on inside a cylinder. However, it was purely optical, and offered no way to take photos or capture digital images.

Since then, borescopes have become much less expensive and feature-rich. For years, I recommended the BK8000 digital borescope (also about $1,000) which provides excellent image quality and the ability to view images on a screen or capture them as JPEG files on a computer.

Vividia Ablescope VA-400

Vividia Ablescope VA-400

Last year, I purchased a Vividia Ablescope VA-400 from Amazon for less than $200. This is an amazingly inexpensive rigid digital borescope with the unique ability to adjust its viewing angle to anything between 0 and 180 degrees. The unit doesn’t come with an imaging device, but it has a USB cable that can be connected to any notebook computer or Android tablet or phone with a micro-USB port. It comes with both PC software and an Android app. This thing is so cheap that it’s now practical for every aircraft owner to have one.

What to look for

Normal valves

Normal valves

Also A&Ps tend to have little or no training in how to use a borescope, it’s certainly not rocket science. Here’s a photo what valves normally look like. The smaller valve on the left is the exhaust valve, while the larger one on the right is the intake valve. The reddish deposits on the exhaust valve and the brownish ones on the intake valve are typical. These deposits should appear reasonably symmetrical, indicating that the valves are rotating in service as they should be.

Burned exhaust valve

Burned exhaust valve

By way of contrast, here’s a photo of a burned exhaust valve. Note the asymmetrical appearance, especially the highlighted region (white arrows) where the deposits are minimal or absent (because that portion of the valve is running too hot). This is the classic visual signature of a burned valve. If the cylinder leaks air past the exhaust valve during the compression check and if the borescope shows this kind of asymmetrical deposit pattern, you can be relatively certain that the valve is burned and that the cylinder has to come off. But if the valve looks normal under the borescope, some leakage during the compression check is not grounds for removing the cylinder. (Now they tell me!)

Cylinder barrels

Cylinder barrels

The borescope is also a great way to check the condition of the cylinder barrel. Ths photo shows two borescope views of the upper cylinder bore—the so-called “ring step area.” The left view is normal; the right one has abnormal wear and scoring—possibly due to a broken compression ring—and probably needs to come off.

Next time you put your airplane in the shop, ask your mechanic what kind of borescope he uses. If your A&P doesn’t have a borescope or doesn’t know how to use one, educate him (and let him know that it’s now required equipment for any mechanic that works on Continental engines)…or find another mechanic.

Pulling a cylinder without first borescoping it is a lot like performing major surgery without first getting a CT or MRI. Don’t let any mechanic do that to your engine.

Mike Busch is arguably the best-known A&P/IA in general aviation, honored by the FAA in 2008 as National Aviation Maintenance Technician of the Year. Mike is a 7,500-plus hour pilot and CFI, an aircraft owner for 45 years, a prolific aviation author, co-founder of AVweb, and presently heads a team of world-class GA maintenance experts at Savvy Aviation. Mike’s book Manifesto: A Revolutionary Approach to General Aviation Maintenance is available from Amazon.com in paperback and Kindle versions.

Checking the Dipstick

Checking the dipstick

There’s a lot more to checking the dipstick than just noting the oil level. The appearance of the oil is at least as important as its quantity.

We’ve been doing it since our earliest days as student pilots. Now that we’re aircraft owners, we still do it as part of our standard preflight ritual. But are we doing it right?

It turns out that there’s a lot more to checking the engine’s oil dipstick properly than just making sure that the oil level is above the minimum-for-flight level listed in the POH. If we really pay attention, we can learn a lot about the condition of our oil and of our engine.

How much oil is needed?

The engines on my Cessna 310 have 12-quart sumps—13 quarts if you include the quart in the spin-on oil filter. When I first acquired the airplane, my mechanic would fill the sump to its maximum capacity at each oil change. It didn’t take me long to discover that the engines didn’t like that, and promptly tossed several quarts out the engine breathers.

My POH states that the “minimum for flight” oil level is 9 quarts. So I asked my mechanic to service the sump to 10 quarts (instead of 12), and I’d add a quart of make-up oil when the level got down to 9 quarts. That worked better, but I was still seeing a fair amount of oil on the underside of the engine nacelles and the outer gear doors.

After I became a mechanic myself and learned about such things, I checked the Type Certificate Data Sheet (TCDS) for my Continental TSIO-520-BB engines, and found that an oil level of 6 quarts was sufficient to make good oil pressure in all flight attitudes from 23° nose-up to 17° nose-down. Armed with this information, I decided to experiment with lower oil levels.

What I discovered was that oil consumption (and the oily mess on the airframe) was drastically reduced if I maintained the oil level at around 8 quarts on the dipstick. Since then, I’ve avoided filling the sump to more than 9 quarts, and I normally do not add make-up oil until the dipstick reads about 7½ quarts. (This still gives me a 1½-quart “cushion” above what the engine needs to operate reliably in all flight attitudes.)

You might wonder why Continental put a 12-quart sump on an engine that requires only 6 quarts. The answer is that FAA certification requirements demand that the engine be designed to hold twice as much oil as it actually needs:

FAR §33.39 Lubrication system.

(a) The lubrication system of the engine must be designed and constructed so that it will function properly in all flight attitudes and atmospheric conditions in which the airplane is expected to operate. In wet sump engines, this requirement must be met when only one-half of the maximum lubricant supply is in the engine.

The TCDS for my TSIO-520-BB engines states that maximum acceptable oil consumption is about one quart per hour. If my engines actually used that much oil, then I’d need to fill the sumps nearly to their maximum capacity to ensure that I had enough oil to make a 5-hour flight without risking oil starvation. But since I know from long experience that my engines use more like 0.1 quart per hour, there’s no reason for me to carry anywhere near that much oil.

Every aircraft engine installation has an optimum oil level at which oil consumption is minimized and the engine is happiest. I would encourage you to experiment to determine what oil level works best for your airplane. Your engine will operate properly at 50% of its maximum oil capacity—guaranteed. As long as you keep the oil level a quart or two above the 50% point, your engine will be happy.

The best time to get an accurate dipstick reading is just prior to the first flight of the day. If you check the oil level shortly after the engine has been run for awhile, the dipstick reading will be noticeably lower because a significant quantity of oil remains adhered to various engine components. Another reading taken 24 hours later will often show an oil level that is ½ to 1 quart higher.

Oil consumption?

Having assured yourself that there’s enough oil in the engine, your next task is to make note of how much oil your engine is using. Keeping track of oil consumption—particularly any significant increase in oil consumption rate—is an important tool for monitoring engine condition.

The most common method of measuring oil consumption is to record how many quarts of make-up oil are added between oil changes, and to divide the total by the number of hours in the oil-change interval. (For example, if the oil is changed after 50 hours and 6 quarts of make-up oil were added during that time, the average oil consumption rate is 50/6 or 8.3 hours per quart.)

Oil consumption graph

Oil consumption isn’t linear—it accelerates as the oil deteriorates over time. The rate of consumption during the first 10 hours after an oil change is a good indication of engine condition.

However, this approach obscures the fact that oil consumption is not linear over the oil change interval. If you keep track of when you add each quart of make-up oil, you’ll find that less oil is consumed at first, and progressively more oil is consumed as the oil’s time-in-service increases.

The reason for this accelerating oil consumption is that the viscosity of the oil decreases as the oil deteriorates. Mineral oils lose viscosity due to a phenomenon called “polymer shearing” in which the long organic molecules are actually broken apart by mechanical action of the engine’s moving parts. Multigrade oils also lose viscosity because their viscosity-index improvers oxidize when exposed to high temperatures.

The increased rate of oil consumption provides tangible evidence that your engine oil is getting “long in the tooth” and ought to be changed soon.

What does your oil look like?

Whenever you check the dipstick, it’s also important to make note of the oil’s appearance—particularly its color and clarity. The oil’s appearance offers valuable clues to its condition and that of your engine.

Oil color

Color and transparency are important indicators of engine condition. When oil becomes dark and opaque, it should be changed. If this happens rapidly, it suggests that the engine has too much blow-by past the rings, or that oil temperature is too hot.

Fresh engine oil has a light amber color and is so transparent that it’s sometimes hard to read the dipstick level. As the oil remains in service, it gradually darkens in color and becomes progressively more opaque.

The darkening of engine oil is caused by contamination and oxidation. Contaminants include carbon (soot), lead salts and sulfur from combustion byproducts that get past the compression rings and into the crankcase (“blow-by”), as well as any dust or dirt that gets past the induction air filter. Oxidation of the oil occurs when it is exposed to high localized temperatures at it circulates through the engine, and results in the formation of coke. Various oil additives are also vulnerable to oxidation, particularly the viscosity-index improvers used in multiweight oils.

Dispersant additives are blended in the oil to help keep these so-called “insolubles” in suspension in order to keep the engine clean and minimize sludge deposits. As the quantity of insolubles in suspension increases, the oil darkens and becomes opaque.

It is important to note how quickly this darkening occurs. If your oil remains relatively light-colored and translucent after 25 hours in service, you can be reasonably confident that your cylinders and rings are in fine condition and that your oil can prudently remain in service for 40 or 50 hours. On the other hand, if your oil gets dark and opaque after 10 or 15 hours, you’d be wise to change your oil more often—perhaps at 25 hours—and you may want to investigate the possibility that one or more cylinders are excessively worn.

Such rapid discoloration is often a good indicator that the oil is distressed. In one study, 90% of oil that appeared abnormally dark on the dipstick was subsequently found by laboratory analysis to be non-compliant with required specifications. Oil that is dark and opaque from blow-by past the rings is very likely to be rich in acids and other corrosive compounds that can attack your cam and lifters, and that’s probably the #1 cause of engines failing to make TBO. Any time your oil appears dark or opaque, you would be wise to drain it and replace it with fresh oil and a new oil filter, regardless of the oil’s time-in-service.

Mike Busch is arguably the best-known A&P/IA in general aviation, honored by the FAA in 2008 as National Aviation Maintenance Technician of the Year. Mike is a 7,500-plus hour pilot and CFI, an aircraft owner for 45 years, a prolific aviation author, co-founder of AVweb, and presently heads a team of world-class GA maintenance experts at Savvy Aviation. Mike’s book Manifesto: A Revolutionary Approach to General Aviation Maintenance is available from Amazon.com in paperback and Kindle versions.

Temperature, Temperature, Temperature

I’ve had wonderful luck with piston aircraft engines throughout my nearly 50 years as an aircraft owner. All the engines on my airplanes have made TBO with minimal maintenance along the way, and in recent years they’ve gone far, far beyond TBO.

For decades, I was convinced that the secret of my success was the fact that I “babied” my engines, typically limiting my cruise power settings to no more than 60 or 65 percent power. I felt that sacrificing a little airspeed in exchange for long engine life and reduced maintenance cost was a good tradeoff.

I’ve come to learn, however, that such “babying” is one way to achieve long engine life, but it’s not the only way. That’s because it’s not POWER that damages out engines—it’s TEMPERATURE. It turns out you can run these engines as hard as you like so long as you are obsessive about keeping temperatures under control.

Or as my late friend, powerplant guru and former Continental Motors tech rep Bob “Mose” Moseley used to say, “There are three things that affect how long your engine will last: (1) temperature, (2) temperature, and (3) temperature!”

It’s all about the heat

CHTOur piston aircraft engines are heat engines. They have moving parts—notably exhaust valves and valve guides—that are continually exposed to extremely high temperatures in the vicinity of 1,500°F and sometimes hotter. Since engine oil cannot survive temperatures above about 400°F, these moving parts must function with no lubrication. They depend on extremely hard metals operating at extremely close tolerances at extremely high temperatures with no lubrication. Aluminum pistons and cylinder heads are also exposed to these very hot temperatures, despite the fact that aluminum melts at about 1,200°F. It’s nothing short of miraculous, and a testament to outstanding engineering, that these “hot section” components last as long as they do.

The key to making these critical parts last is temperature control, and the most important temperature is cylinder head temperature (CHT). Mose monitored and overhauled these engines for nearly four decades, and he swore to me that an engine that is operated at CHTs above 400°F on a regular basis will show up to five times as much wear metal in oil analysis as an identical engine that is consistently limited to CHTs of 350°F or less. “It’s amazing how much a small increase in CHT can accelerate engine wear,” Mose said.

As critical as CHT is, many owners don’t have a clue whether their CHTs are 400°F+ or 350°F-. That’s because the engine instrumentation provided by most aircraft manufacturers is pathetically inadequate. The typical factory CHT gauge looks at only one cylinder, and it’s not necessarily the hottest one. Further, the typical factory CHT gauge often isn’t even calibrated, and its green arc extends up to a ridiculously hot 460°F (for Continentals) or 500°F (for Lycomings). Those numbers may be okay as emergency red lines, but they’re horribly abusive for continuous operation. If all you have is factory gauges, you could easily be cooking your cylinders to death while blissfully thinking that all is okay because the CHT gauge is well within the green arc.

To know what’s really going on in front of the firewall, you have to have a modern multiprobe engine analyzer with a digital readout. Such instrumentation isn’t cheap—figure $2,500 for a single or $5,000 for a twin, installed—but if it saves you from having to replace a couple of jugs en route to TBO, it has more than paid for itself. Installing a digital engine analyzer is probably the best money you can spend on your airplane.

Fuel system setup

MaintenanceFor takeoff and initial climb, we normally are at wide-open throttle, full-rich mixture, maximum RPM (if we have a constant-speed prop), and wide-open cowl flaps (if we have those). So there’s not much we can do from the cockpit to affect CHT during these phases of flight.

What does affect CHT is how our full-power fuel flows are adjusted. Unfortunately, it is shockingly common to see damagingly high CHTs due to improperly adjusted fuel flows, particularly in fuel-injected engines. It is not unusual for the fuel flows to be set wrong from the day an engine is installed, and never to be checked or adjusted all the way to TBO. The owner winds up going through cylinders every 500 hours and never knowing why (or blaming the manufacturer).

In part, the problem lies with mechanics who don’t fully understand how critical it is to test and adjust the fuel system setup on a regular basis. Continental recommends that the fuel system setup on its fuel-injected engines be checked and adjusted several times a year to account for seasonal changes. I’ll grant that’s a bit anal, but most Continental-powered airplanes go year after year without this ever being done, and many shops that maintain these airplanes don’t even have the necessary test equipment to do it.

Even when mechanics do test and adjust the fuel system, they often adjust it wrong. For example, Continental Manual M-0 (formerly SID97-3G) contains a lengthy table that specifies full-power fuel flow as a range (minimum and maximum). The “fine print” instructs mechanics to adjust the full-power fuel flow to the high end of the specified range, but many mechanics miss this subtlety and adjust it to the middle of the range. Experience shows that this is simply not enough fuel flow to keep CHTs cool during hot-weather takeoffs.

Lycoming engines with RSA fuel injection have no field adjustments for takeoff fuel flow. If it’s inadequate, the fuel servo has to be sent in to a specialty shop for bench checking and adjustment.

Then there’s the problem of aftermarket engine modifications. For example, engines that have been retrofitted with Superior’s Millennium cylinders often run higher CHTs than they did with their original factory cylinders. That’s because Millennium cylinders have substantially better “volumetric efficiency” than factory cylinders—in other words, they breathe better. Since they breathe more air during every combustion cycle, they need more fuel to maintain the same fuel/air mixture. The full-power fuel flow marked on your fuel-flow gauge may simply not be high enough if you have Millennium cylinders installed.

Even worse are turbocharged engines with aftermarket intercoolers installed. The intercooler reduces the temperature of the air that the cylinder breathes, making it denser. Denser air demands more fuel to maintain the desired fuel/air mixture, so full-power fuel flow must be increased significantly above original factory specifications. Too often this is not done, and the result is fried cylinders.

Many A&Ps are reluctant to adjust takeoff fuel flow above red-line. However, if you have Millennium cylinders, an aftermarket intercooler, or some other “mod” that allows your engine to produce more power than it did when it left the factory, that’s exactly what must be done to keep your CHTs cool and avoid premature cylinder failure.

Enough fuel flow?

MP and FF guage comboHow can you tell if your full-power fuel flow is adequate? If you’re limited to factory gauges, you probably can’t, at least with any precision. About the best you can to is to watch your fuel flow gauge (if you have one).

A good rule of thumb is to multiply your engine’s maximum rated horsepower by 0.1 to obtain the minimum required fuel flow in gallons-per-hour, or by 0.6 for pounds-per-hour. For example, if your engine is rated at 285 horsepower, your takeoff fuel flow should be at least 28.5 GPH; if it’s rated 310 horsepower, the minimum should be 31.0 GPH. If your takeoff fuel flow is significantly less than this, have your mechanic crank it up. And don’t forget that if you have Millennium cylinders or an aftermarket intercooler, your engine might be producing a few percent more horsepower than what the book says, so it might need a few percent more fuel flow.

Now if you have a digital multiprobe engine analyzer, it’s easy to tell if your fuel flow is adjusted high enough. Just make sure none of your CHTs exceed 380°F during takeoff and climb for Continentals or 400°F for Lycomings. Lower is even better.

What about cruise?

Cruise flight represents the lion’s share of our flying time. Just as in takeoff and climb, it’s essential to keep all our CHTs at or below 380°F (for Continentals) or 400°F for Lycomings during cruise to achieve good cylinder longevity, and lower is even better. There are basically three different strategies for keeping CHTs low during cruise:

  • Baby the engine
  • Operate very rich
  • Operate lean-of-peak

All three strategies work, and conscientious use of any of them will give you a good shot at making TBO with minimum cylinder problems. But each has its pros and cons. Let’s take a closer look.

Engine graph

The mixture that many POHs refer to as “recommended lean mixture” is 50°F rich of peak EGT. As this graph shows, using that mixture results in very nearly the highest possible CHT. To reduce CHTs to the level required for good cylinder longevity, you need to do one of three things: (1) reduce power, (2) operate very rich, or (3) operate lean-of-peak.

Baby the engine

Many POHs talk about operating at three alternative mixture settings: “best power mixture” (~125°F rich-of-peak), “recommended lean mixture” (~50°F rich of peak, and “best economy mixture” (~peak EGT). It turns out that “recommended lean mixture” (~50°F ROP) is just about the worst possible mixture setting for keeping CHT low.  If you look at Figure 1, you’ll see that CHT reaches a maximum very close to 50°F ROP. So if you want to operate at “recommended lean mixture” and simultaneously keep CHT low, there’s only one way to get there: reduce power dramatically (generally 65% power or less). In other words, baby the engine.

Both “best power mixture” (~125°F ROP) and “best economy mixture” (~peak EGT) result in somewhat lower CHTs than does “recommended lean mixture.” At either of these mixture settings, you can usually operate at 70% power or so and still keep CHTs in the acceptable range.

In any of these cases, you’re trading power and airspeed for reduced temperatures and increased longevity. For most of us, that’s a reasonable tradeoff to make.

Operate very rich

But what if you are unwilling to sacrifice power and airspeed? Is it possible to go fast and still keep CHTs low?

Sure it is. We already talked about one way to do this in our discussion of takeoff and initial climb: pour lots of 100LL on the problem. In other words, operate very rich.

How rich? Figure 1 suggests that to reduce CHTs by 25°F, you need to enrich the mixture to about 160°F ROP. For each additional 10°F of CHT reduction, you need to enrich an additional 50°F ROP. Using such very rich mixtures, you can go fast and still stay cool. (This is how Reno racers usually operate.) But before you decide to go this route, consider the downsides.

The most obvious downside is that this strategy is very fuel-inefficient. Compared to “best economy mixture,” the very-rich strategy consumes about 25% more fuel, and reduces range by a similar amount. Advocates of very rich mixtures will tell you that “fuel is cheaper than engines,” but don’t be so sure. At today’s avgas prices, using 25% more fuel in a 300 horsepower engine can cost more than $40,000 over the engine’s TBO, and that’s enough to change out quite a few cylinders.

A second and less obvious downside is that very rich mixtures result in “dirty” combustion with lots of unburned byproducts in the exhaust gas. Operating this way for long periods of time tends to cause deposit buildup on piston crowns, ring grooves, spark plugs and exhaust valve stems. Do it long enough and you could wind up with stuck rings, stuck valves, worn valve guides, and fouled plugs.

Operate lean-of-peak

The third way to reduce CHTs is to lean even more aggressively than the POH recommends and operate on the lean side of peak EGT. Figure 1 shows that you can reduce CHTs by 25°F by leaning to about 10°F LOP. For each additional 10°F of CHT reduction, you need to lean an additional 15°F LOP. Using these very lean mixtures, you can go fast, stay cool, and obtain outstanding fuel economy, all at the same time.

What’s the downside of the LOP approach? The only major downside is that if your engine has uneven mixture distribution among its cylinders, it will usually run unacceptably rough at LOP mixture settings.

Uneven mixture distribution can usually be corrected in fuel-injected engines by “tuning” the fuel injector nozzles to eliminate the mixture imbalances. GAMIjectors are tuned nozzles that are STC’d for the majority of fuel-injected Continentals and Lycomings. Continental now offers its own version of tuned injectors on some of its premium engines.

If your engine is carbureted, you have no injector nozzles to tweak. Most carbureted Lycomings have pretty decent mixture distribution and can be run at least mildly LOP without running rough. Some carbureted Continentals (notably the O-470 used in the Cessna 182) have miserable mixture distribution, making it difficult to run those engines LOP without uncomfortable roughness.

Stay cool!

Whatever strategy you prefer, the important thing is to keep a close watch on your CHTs and ensure that they remain cool. The best way to do this is to install a multiprobe digital engine monitor and program its CHT alarm to go off at 390°F (Continentals) or 410°F (Lycomings). If the alarm goes off during takeoff or initial climb, you’re going to have to get your mechanic to turn up the full-power fuel flow.  If it goes off during cruise, either enrich (if ROP) or lean (if LOP) to bring the CHT down to acceptable levels.

If you don’t have a multiprobe digital engine monitor, install one. The cost of such instrumentation (including installation) is usually less than the cost of replacing one cylinder. Failure to install such instrumentation is a classic case of “penny wise, pound foolish.”

Mike Busch is arguably the best-known A&P/IA in general aviation, honored by the FAA in 2008 as National Aviation Maintenance Technician of the Year. Mike is a 7,500-plus hour pilot and CFI, an aircraft owner for 45 years, a prolific aviation author, co-founder of AVweb, and presently heads a team of world-class GA maintenance experts at Savvy Aviation. Mike’s book Manifesto: A Revolutionary Approach to General Aviation Maintenance is available from Amazon.com in paperback and Kindle versions.

Fix It Now!

Sometimes I simply cannot fathom what makes aircraft owners do some of the things they do. Particularly amazing to me are some of the mechanical problems that aircraft owners elect to live with rather than fix.

Now I’m just as averse to spending money as the next guy (and probably more than most). In fact I’ve made something of a crusade out of saving money on aircraft maintenance, and built a company dedicated to helping my fellow aircraft owners how to do the same.

On the other hand, I have always had something close to a zero-tolerance policy about mechanical problems. When something isn’t right on my airplane, it drives me nuts until I fix it. Invariably I fix such problems right away, rather than putting them off.

Nearly five decades as an aircraft owner has taught me that it’s usually cheaper to fix a problem sooner rather than later…sometimes a great deal cheaper. Not to mention that continuing to fly with a known mechanical deficiency can sometimes be hazardous to your health.

Fuel leak

Apparently some aircraft owners don’t share my fix-it-now philosophy. Check out this email I received from an aircraft owner:

Shortly after I bought my airplane last year, I noticed a drip coming from under the aircraft which pooled just to the left of the nosewheel. The drip occurred with the frequency one drip probably every five seconds while the aircraft sat static with the fuel selector on either the left or right tank. Obviously one of the very important shutdown tasks for me was to turn the fuel selector off in order to stop the leak. I never established whether the fuel leaked while the engine is running.

After not flying for the past month, I went out to my airplane last week. The aircraft was leaking fuel despite the selector being in the off position. There was a big pool of avgas beneath the airplane, and the fuel gauges indicated that I had lost almost all the fuel in my tanks…at $4.75 a gallon!

Not understanding why the fuel now leaked regardless of fuel selector setting, I started the aircraft, taxied it around to warm-up the engine and then left it at the maintenance hanger.

I am being told by the very competent maintenance supervisor that originally it was simply a fuel selector gone bad. However, they are now telling me that given that the aircraft now leaks in any position, it’s also a bad engine driven fuel pump. Usually I’d say let’s fix the selector and see if that resolves the problem altogether but I am concerned about the fuel pump going out at some critical time. Please advise.

Here we have an owner who knowingly flew his airplane for a year with a known significant fuel leak in the engine compartment. He only brought it to the attention of his mechanic when he could no longer stop the leak when the aircraft was parked by turning off the fuel selector. Now he’s asking whether it would be okay to fix the fuel selector and continue flying with the fuel leak in the engine compartment unaddressed.

Fuel Leak

A running fuel leak is NOT something that can prudently be deferred. Fix it now!

Good grief! I cannot imagine operating my LAWNMOWER with a known fuel leak, much less my airplane. What is this owner thinking?

Exhaust leak?

While still scratching my head over that one, I heard from the owner of a Cessna 340 that made me start scratching my head again:

I don’t push the engines hard, running at 65% power or lower most of the time. However, despite a published service ceiling of 27,000 feet, the engines really don’t perform well over 15,000 feet. I routinely fly over that altitude, but the cylinder head temperatures get a little high, and the engines burn more oil.

Sometimes I have trouble with the wastegates functioning properly at altitude, too, and I get some bootstrapping of manifold pressures (needle separation), which is unpleasant at best (because the engines get out of sync), and is dangerous at worst (because the bootstrapping could be due to an exhaust manifold leak). So as a practical matter, I only climb over 21,000 if it is absolutely necessary.

It baffles me how this owner can be sufficiently knowledgeable to recognize that his aircraft has a turbocharging problem that prevents it from operating properly at altitude, and even understands that the problem could well be due to an exhaust leak, yet continues to fly the aircraft with that known deficiency.

Exhaust Leak

An exhaust leak at the cylinder exhaust port if caught early can often be fixed with a cheap gasket. If you let it go, you’re probably looking at a costly cylinder rework job, or in extreme cases (as shown here) a whole new cylinder.

Doesn’t he understand that turbocharged twin Cessnas have a ghastly history of exhaust-related accidents, many of them fatal? Doesn’t he know about AD 2000-01-16 that requires repetitive inspection of his exhaust system every 50 hours, and pressure testing at every annual inspection? What is this owner thinking? (For that matter, what is his A&P thinking?)

Starter adapter slipping

The beat goes on. Here’s a post I saw recently on a popular Internet aviation forum:

On my departure from Pensacola on Sunday afternoon, I turned the key to start the engine (a Continental IO-520) and I could hear the starter motor, but the prop wouldn’t turn. It did actually turn slightly, but then just sat there.

I have noticed frequently in the past that the prop turns a little and then stops and then a second or two later it continues. Once the prop starts turning, the engine usually fires on the first turn and starts right up.

On my previous airplane, my A&P told me to turn the prop until I hear the click and it would help to start. So I turned everything off, got out of the plane and turned turn the prop by hand until I heard it click. I turned it again until I heard it click a second time just for good measure. I then got back in the plane and it fired right up like normal.

When I stopped for fuel at Zephyrhills on the way home, the engine started right up with out having to do the prop trick. I figured I would monitor it and if it acted up again to call in my A&P for a surgical procedure, but after thinking about it this morning I thought I would come to the forum here and see what others have to say.

Replies to this owner’s post explain that he was suffering from the classic symptoms of a TCM starter adapter that is severely worn and slipping. What bothers me is that the owner’s description makes it obvious that he’s been aware of this slippage problem for a long time, yet did nothing about it. Even after the slippage got so severe that he nearly found himself stranded in Pensacola, his first thought was to “monitor it” and only bring it to the attention of his A&P “if it acted up again.”

Continental Starter Adapter

If you try to start a Continental engine and the starter motor turns but the prop doesn’t, you can bet that the starter adapter is slipping (top). This indicates that the spring and shaftgear (lower left and right) are worn. If you catch the problem early, it can be repaired for a few hundred dollars by installing an undersize spring. If you let it go, you may wind up buying a new shaftgear for thousands of dollars, or perhaps even a new engine for tens of thousands.

This owner’s approach was clearly to do nothing about the starter adapter slippage until it becomes so bad that he simply cannot tolerate it any more. This is truly a “penny wise, pound foolish” attitude because every time a Continental starter adapter slips, it “makes metal” inside the engine. If the owner is really lucky, most of that metal will be caught by the oil filter and won’t circulate through the engine and contaminate the bearings and plug up the small passages in the hydraulic valve lifters. If he’s not so lucky, he could easily find himself buying a $30,000 engine overhaul.

Yet this owner is hardly alone. Countless owners of Continental-powered aircraft have slipping starter adapters, but elect to live with the problem rather than fix it. Not smart.

Fix it now!

I could go on and on with similar examples, but by now I’m sure you’ve got the idea. Any time you become aware of something on your aircraft that isn’t quite right, the smart thing to do is to bring it to the attention of your mechanic pronto. If the mechanic agrees that the problem is one you can prudently defer fixing until the next scheduled maintenance cycle, fine. But it’s often the case that the fix-or-defer decision is a “pay me a little now or pay me a lot later” proposition.

An exhaust leak at an exhaust riser flange might be solved with a simple gasket if addressed early. If left unaddressed until the cylinder exhaust flange has been severely eroded, the jug will probably have to come off for expensive rework or replacement.

A slipping Continental starter adapter if caught early can usually be fixed for less than $1,000 by installing an undersize spring. If allowed to continue slipping until the shaftgear is worn beyond limits, you’re looking at many thousands of dollars to repair—or if you get unlucky, a new engine.

A fuel leak caught early can often be fixed by tightening a B-nut or replacing a chafed line. If ignored, it can cause a fire, loss of the aircraft, and perhaps even loss of life.

So don’t just scribble the discrepancy on a post-it note so you can squawk it at the next annual inspection. Fix it now—or at least discuss it with your mechanic before making a fix-or-defer decision. It’s the smart and prudent thing to do, and it might just wind up saving you big bucks.

Mike Busch is arguably the best-known A&P/IA in general aviation, honored by the FAA in 2008 as National Aviation Maintenance Technician of the Year. Mike is a 7,500-plus hour pilot and CFI, an aircraft owner for 45 years, a prolific aviation author, co-founder of AVweb, and presently heads a team of world-class GA maintenance experts at Savvy Aviation. Mike’s book Manifesto: A Revolutionary Approach to General Aviation Maintenance is available from Amazon.com in paperback and Kindle versions.

The most dangerous thing in aviation?

AOPAfileToolsThere’s an old joke among aircraft mechanics that “the most dangerous thing in aviation is an aircraft owner with a screwdriver.” (Or a wrench, or a toolbox, or a Swiss army knife…)

For many mechanics, this is no laughing matter. I’ve been advocating owner involvement and participation in maintenance for many years, and I’ve gotten a fair amount of push-back from repair station owners and working A&Ps who think I’m doing aviation a great disservice through this advocacy, and feel strongly that aircraft maintenance should be left strictly to the pros (like them).

It’s not hard to understand where this idea originates. I doubt there exists a working general aviation mechanic anywhere who doesn’t have a few dozen horror stories about owner-performed maintenance nightmares he’s found while working on GA aircraft—automotive hoses used in fuel systems; exhaust leaks patched with fiberglass and epoxy; rat’s-nest wiring full of Home Depot plastic-insulated doorbell wire, Scotch electrical tape, Pep Boys’ automotive crimp connectors and cold solder joints; … well, you get the idea. I’m the first to admit that I, too, have seen stuff like this in airplanes that really made me shudder.

(But then again, I’ve also seen plenty of things done by allegedly professional A&P mechanics that made me shudder. Unfortunately, the fact that someone holds an FAA certificate—whether it be a pilot certificate or a mechanic certificate—is no guarantee that he isn’t a jerk.)

Some of the best-maintained aircraft I’ve ever seen are ones maintained largely by their non-A&P-rated owners. After all, no one is more motivated to do a first-class job of maintenance than the person whose posterior and those of his family are on the line.

Some of the most mechanically magnificent GA aircraft I’ve ever seen are kitplanes entirely built and maintained by their owners. I suspect the average homebuilt is better maintained than the average “professionally maintained” spam can.

Let’s face it: There are plenty of aircraft owners who have the knowledge, skill and desire to work on their own aircraft and do a first-class job. On the other hand, there are also lots of aircraft owners who have little or no mechanical aptitude or inclination. Most readily admit that they are mechanically challenged individuals (a.k.a. “all thumbs”) and happily leave the wrench swinging to the pros at their maintenance shop.

Then there are a small minority of owners who tinker with their aircraft even though they don’t know which end of the screwdriver to hold, and wind up doing things that are illegal and unsafe. These are the folks that A&P jokes and horror stories are made of, but in truth they represent only a tiny minority of owners.

You won’t save money

There are lots of reasons to consider getting involved in swinging wrenches on your own aircraft, but generally saving money isn’t one of them. While the labor rates at maintenance shops aren’t exactly cheap, the fact is that you’d probably take an hour to accomplish what a professional A&P can do in 20 minutes. At least that was my experience when I started swinging wrenches on my airplane more than 15 years ago, and that of several aircraft-owner friends who do their own maintenance. Even though I now have a lot more experience and hold an A&P/IA, I’m still a lot slower than a career mechanic who swings wrenches every day.  As owner-mechanics, we consider ourselves safe, competent and careful … but slow.

Think about it. A working A&P can hang a cylinder on an engine in 20 minutes or so. No big deal—install the base O-ring, pre-oil the barrel, insert the piston into the barrel using a ring compressor, lift the jug into position, slide the wrist pin through the piston and con rod, push the jug over the studs, thread on the hold-down nuts, and then torque them into place.

But when I hang a jug, I spend 20 minutes watching the Continental video just to make sure I remember all the necessary steps (since the last time I hung a jug was three years ago), and another 10 minutes looking up the torque values and torque sequence (stuff any working A&P knows from memory because he changes jugs every week). Then I waste five minutes trying to remember where I put my cylinder base wrenches, and another 15 minutes going next door to borrow a 5.25-inch ring compressor. And so it goes.

In other words, when I swing wrenches on my airplane, my work is careful, meticulous, strictly by-the-book … and pathetically slow. I suspect the same is true of most owner-mechanics who only go through one annual inspection a year instead of dozens.

So unless you value your time at less than one-third of your A&P’s shop rate, you’re money ahead to let him do the work.

So why do it?

Good question.

I owned airplanes for 20 years before I first had any interest in picking up a wrench. I never would have guessed that I’d become involved in aircraft maintenance.

After owning a succession of single-engine airplanes, I bought my Cessna T310R in 1987. Eighteen months later, the A&P who had been doing my maintenance relocated, and the mechanic who took his place was relatively young and inexperienced and made me a little nervous. So when the airplane went into the shop for its annual inspection, I decided to hang around and watch, just for peace of mind.

It wasn’t long before “hang around and watch” turned into “hang around and help.” Lots of mechanics wouldn’t have put up with me, but this one did—in fact, he seemed to appreciate my interest, and was very patient in answering my questions and showing me the ropes of basic aircraft maintenance.

Much to my surprise, I found the hands-on work oddly therapeutic—a sharp contrast to my normal daily routine (“slaving over a hot computer keyboard”). I’ve always enjoyed learning new things (my wife calls me a professional student), and I found myself intrigued by how much there was to learn about aircraft maintenance in general and about my Cessna T310R in particular.

Over the next few years I found myself taking on more and more of the maintenance work myself, under the patient supervision of a succession of A&Ps. Clearly, I was hooked.

As I started doing more and more of my own maintenance, I discovered that my aircraft became mechanically better and better. In my past aircraft ownership experience, my airplanes always seemed to have a few squawks waiting for the next time the plane went into the shop. Now, even though the T310R was by far the most complex airplane I’d ever owned, I discovered that it was virtually squawk-free. When anomalies did arise, I’d find myself fixing them immediately, rather than letting them stack up.

So why consider owner-performed maintenance? In my case, the answer is “satisfaction.” The satisfaction that comes from doing something with your hands; from learning something new and complex; from getting to know a complicated piece of machinery in a way that that cannot be achieved without taking it apart and putting it back together; and from flying a squawk-free airplane that receives the finest maintenance that dedication (not money) can buy.

Getting started

Will aircraft maintenance give you the same kind of satisfaction that it does me? There’s only one way to find out, and that is to try it. Remember, I never thought of myself as a wrench-swinging kind of guy—until I tried it and (surprise!) discovered that I liked it.

Regardless of how you think you feel about aircraft maintenance, I strongly suggest that every aircraft owner go through at least one owner-assisted annual inspection. It’ll cost you a week or two out of your busy schedule (consider it a novel vacation idea), and you’ll learn more about your aircraft’s design, construction and condition than you can possibly imagine. You’ll also learn a lot about yourself. You might discover that you enjoy working on your airplane, maybe even that you’ve got a knack for it. Or perhaps that you hate it and/or have absolutely no aptitude for it.

I also suggest you learn how to do some basic preventive maintenance on your airplane—at least how to change the oil and oil filter, and perhaps to clean, gap and rotate the spark plugs. This involves only a couple of hours of work—even the busiest aircraft owner can do it over a weekend. The real beauty of doing your own oil and filter changes—besides the fact that it saves you the hassle of taking your plane to the shop every 25 to 50 hours—is that it forces you to remove the engine cowlings regularly and get up-close-and-personal with your engine. It’s the sort of inspection that pilots really ought to be doing every preflight, but unfortunately can’t be done on most of today’s tightly-cowled aircraft except at oil-change time. Think of an owner-performed oil change as an “advanced preflight.”

What can you do legally?

The FAA has carved out a broad laundry list of so-called “preventive maintenance” tasks that a pilot-rated owner can perform on his aircraft without requiring supervision or sign-off from an A&P mechanic. The relevant regulation is 14 CFR 43.3(g), which reads:

The holder of a pilot certificate issued under Part 61 may perform preventive maintenance on any aircraft owned or operated by that pilot which is not used under Part 121, 129, or 135.

The definition of “preventive maintenance” appears in Appendix A(d) of 14 CFR Part 43, and most owners are surprised to learn just how much maintenance they’re allowed to do on their own recognizance. As an owner/operator, you’re permitted to:

  • Change engine oil
  • Replace fuel and oil filters
  • Service spark plugs
  • Service hydraulic fluid
  • Service battery
  • Lubricate just about anything
  • Change tires and tubes
  • Grease wheel bearings
  • Service landing gear struts
  • Replace fuel/oil hoses
  • Install safety wiring and cotter pins
  • Replace landing and position lights
  • Repair landing light wiring
  • Replace the battery
  • Remove and replace tray-mounted radios (except DMEs and transponders)
  • Change database cards
  • Paint anything except balanced flight controls
  • Repair upholstery
  • Replace side windows
  • Replace seats
  • Replace safety belts
  • Patch airframe, fabric

…and that’s just what you can do on your own without a mechanic’s supervision.

With the cooperation of your friendly neighborhood A&P, there’s almost no maintenance task you can’t do. Here’s what 14 CFR 43.3(d) has to say about that:

A person working under the supervision of [an A&P] may perform … maintenance, preventive maintenance, and alterations … if the supervisor personally observes the work being done to the extent necessary to ensure that it is being done properly and if the supervisor is readily available, in person, for consultation.

In other words, you can do anything that your A&P will let you do (and agrees to supervise and sign-off). In this context, “supervise” means whatever your A&P says it means—the reg says he has to be available for consultation, but that doesn’t mean he has to watch your every move or breathe down your neck. As you earn the trust of your supervising A&P, he’ll probably let you do more and more of your own work and simply drop by to inspect it once you tell him you’re done.

How do you earn your A&P’s trust? Keep in mind that he doesn’t expect you to be an expert—in fact, coming across like a know-it-all is a good way to scare off your mechanic. What’s most important is to demonstrate to your A&P that you know your limits, and that he can trust you to stop and consult with him any time you’re not absolutely sure of what you’re doing. Exhibit a careful, conscientious and humble approach, and your A&P will probably give you lots of latitude.

So try it. You might just like it.

Mike Busch is arguably the best-known A&P/IA in general aviation, honored by the FAA in 2008 as National Aviation Maintenance Technician of the Year. Mike is a 7,500-plus hour pilot and CFI, an aircraft owner for 45 years, a prolific aviation author, co-founder of AVweb, and presently heads a team of world-class GA maintenance experts at Savvy Aviation. Mike’s book Manifesto: A Revolutionary Approach to General Aviation Maintenance is available from Amazon.com in paperback and Kindle versions.

Don’t Shoot Yourself in the Foot

How To Shoot Yourself in the FootOver the years, I’ve spent a lot of time hanging around maintenance shops like the proverbial fly on the wall, watching the comings and goings of airplanes and owners and listening to the mechanics talk. In the process, I’ve noticed that owners often wind up inadvertently sabotaging the maintenance of their aircraft by imposing inappropriate time or money pressures.

Deadline

FridayOne of the worst things an owner can do is to put his aircraft in the shop on Monday for an annual inspection and tell his mechanic “Bill, I’ve just gotta have the airplane by Friday…big weekend family trip!” A week might be enough time to get the work done if there are no surprises, but maintenance is seldom surprise-free.

In the case of an annual that starts on Monday, it might well be Tuesday afternoon or Wednesday morning before the IA has gotten the aircraft all opened up, inspected everything, and actually knows what repairs need to be done and what parts need to be ordered. Now the mechanic is working with a gun to his head. In a good-faith attempt to please you (and avoid a confrontation when your aircraft isn’t ready when promised), he’s likely to rush the work and defer any maintenance that is less than absolutely safety-critical.

Lather, rinse, repeat a few times, and you wind up with an aircraft that isn’t as well maintained as it should be. Is that really what you want? Not to mention you’ll be launching off on your big trip in an aircraft just out of annual without leaving time for a proper post-maintenance shakedown flight (sans passengers). Not smart.

Whenever you put your plane in the shop for annual inspection or major maintenance, be prepared for the plane to be downed for twice the estimated time. Tell yourself that when it comes to aircraft maintenance, it’s better to do it right than to do it fast. If the airplane is done on time, be pleasantly surprised. If it runs over due to unforeseen contingencies, keep your cool and be happy that your mechanic cares enough to do the job right.

Sticker shock

Fighting over moneyAlso high on the shoot-yourself-in-the-foot list is arguing over the bill after your aircraft comes out of annual or major maintenance. This is a great way to win the battle but lose the war. At next year’s annual inspection, your mechanic will remember last year’s argument, and will do everything in his power to keep it from happening again—by deferring any maintenance that is not absolutely critical in a good-faith attempt to minimize the bill. Those deferred items will inevitably come back to bite you, because in the long run it’s always cheaper to fix problems sooner rather than later.

Let me be clear: I’m not advocating a money-is-no-object approach to maintenance. Anyone who knows me or has read my stuff knows that I’m a world-class skinflint who will do almost anything to avoid spending a nickel more than necessary on maintenance. But arguing over the bill after the job is done is not the way to save money, trust me. All it will accomplish is to sabotage the quality of maintenance you receive.

Get involved!

Dirty handsIf you want to keep control over the cost of maintenance (and I’m definitely in favor of that), the way to do it is to get involved early in the process. Tell the IA to call you as soon as he’s completed the inspection but BEFORE he’s started any repairs or ordered any parts.

When the IA calls, pay him a visit and go over the discrepancy list with him. Ask him to give you a time and cost estimate to repair each item on the list. For items that aren’t safety-critical (yet), make a joint decision whether to fix now or defer. (In my experience, most owners will elect to fix more and defer less than what the mechanic would decide on his own.)

When you’re done going through the discrepancy list with your IA, you’ll have a pretty solid estimate of what the final bill will be, so there shouldn’t be any unwelcome surprises. And your mechanic will know that his final bill had better be pretty close to the estimate he gave you, or he’d better have a darn good explanation for why it isn’t.

There’s no better way for an owner to learn how to work effectively with mechanics than to do an owner-assisted annual. By the time you’re through, you’ll have learned how the process works and have a much better idea of how things look on the other side of the wrench. I think every owner owes it to himself to go through this experience at least once. Even if you never do it again, the knowledge you’ll gain will pay dividends for as long as you own an aircraft.

Mike Busch is arguably the best-known A&P/IA in general aviation, honored by the FAA in 2008 as National Aviation Maintenance Technician of the Year. Mike is a 7,500-plus hour pilot and CFI, an aircraft owner for 45 years, a prolific aviation author, co-founder of AVweb, and presently heads a team of world-class GA maintenance experts at Savvy Aviation. Mike’s book Manifesto: A Revolutionary Approach to General Aviation Maintenance is available from Amazon.com in paperback and Kindle versions.

Aircraft Owners, Keep Out!

The aircraft owner was obviously frustrated. He’d been searching for a good shop to perform an owner-assisted annual on his airplane:

“It’s getting harder all the time to find a shop that will allow any owner involvement in an annual inspection. The ones I’ve found that will allow it always seem to be mechanics I’d rather not work on my airplane. They may be good mechanics, but they don’t have any type-specific experience working on twin Cessnas and don’t want to take the time to look up the correct procedures in the service manual.

“At the other end of the spectrum, the big shops that have a lot of  experience with my make and model, but seem unwilling to let owners watch, much less assist. They also tend to be expensive, partly because they insist on doing everything strictly by the book.

“The manager of one well-known specialty shop told me that they absolutely insist on doing a complete landing gear re-rigging at every annual, and that they also require 500-hour magneto inspections, claiming that these things are mandatory under the FARs.

“Now, I’m not arguing that these things shouldn’t be done, but are they really required by regulation? I’d be more comfortable if the shop manager told me that these things were strongly recommended, not that they were required. Now I’m starting to wonder whether this shop would refuse to sign off an annual inspection if an engine were past TBO?”

I suspect that many owners share these frustrations. It turns out that there are some valid reasons why big shops often tend to appear less flexible and owner-friendly than smaller ones.

Business concerns

Like it or not, aircraft repair shops are businesses, and some shop managers feel that they simply cannot operate in a businesslike fashion if owners are hanging around the shop. Here are the sentiments of the manager of a Texas shop with a superb reputation for top-notch maintenance:

“We couldn’t get anything done if we let the owners in the shop on every plane we worked on. It’s a distraction. You simply can’t run a business with the owner breathing down your neck. Think about your business—do you allow your customers to watch what you do and see the inner-workings of your business?

“Some owners who work on their own aircraft are knowledgeable and highly motivated. Unfortunately, you need a bit more than that to do quality work on an aircraft. You have to do it day after day, year after year. There’s no substitute for experience.

“We have at least five planes crammed in out shop at all times with more waiting. We’re booked year-round, and every owner wants their plane NOW!

“I think a knowledgeable owner is a good thing. But owners should be careful about doing their own work on critical airworthiness items such as rigging, engine, or mags. Saving money should never be your bottom-line when it comes to maintenance and repairs of your aircraft. That’s fool’s gold….”

As a hands-on aircraft owner who believes passionately in owner-involved maintenance, I frankly don’t care one bit for the attitude expressed by this shop manager. As a businessman, however, I can appreciate why he feels the way he does. If I were in his shoes, perhaps I would feel the same way.

Liability concerns

Another major factor in the increasing reluctance of shops to allow owners to perform maintenance under supervision is heightened concerns about liability, stemming from the General Aviation Revitalization Act of 1994 (GARA), which took aircraft manufacturer’s off the hook for product liability for GA aircraft older than 18 years. An unintended consequence of this law has been a huge increase in litigation against mechanics are repair shops, and a corresponding increase in their concerns about liability.

An aggravating factor is the difficulty of obtaining Errors & Omissions (liability) insurance for GA repair shops. Only a tiny handful of companies are still willing to write such insurance any more, and those that do charge an arm and a leg for the coverage.

In the old days, mechanics and shops only had to worry about whether the work they were doing was safe and legal. Nowadays, they worry increasingly about “how it will look in front of a civil jury” and that’s a whole different kettle of fish.

The result is that many of the biggest and best maintenance shops in the country will no longer consider owner-assisted annuals and other supervised owner maintenance. As an aircraft owner, you need to decide for yourself whether a shop’s reputation for doing outstanding maintenance outweighs its aversion to owner involvement and efforts to save money.

Repair station rules

Another huge problem arises when the shop involved is an FAA-approved Repair Station, as is the case with many large shops. Repair stations are certificated under Part 145 of the FARs, and their operations are governed by a thick FAA-approved Repair Station Manual (RSM).

The RSM specifies exactly what kinds of maintenance and alterations the shop is allowed to do, which shop personnel are permitted to perform which tasks, and what procedures will be employed in performing, inspecting, and approving the work. Frequently, the wording of the RSM prohibits or severely restricts work being done by non-employees (including customers).

To make matters worse, Part 145 now requires each Repair Station to implement an FAA-approved training program for its personnel. The rule requires that work done by the Repair Station be performed by individuals who have received specific initial and recurrent training for the tasks they are performing.

This new rule is undoubtedly a step in the right direction to help assure that only competent people will swing wrenches on our aircraft. Unfortunately, it’s also another major stumbling block for the maintenance-involved owner who wants to work on his airplane under supervision.

The bottom line is that owners wishing to do an owner-assisted annual will probably have to steer clear of shops that operate as Part 145 Repair Stations.

Required or recommended?

Owner-Assisted AnnualWhat about the shop that insists on doing a full annual landing-gear rigging or 500-hour magneto inspections? Granted these are things that really ought to be done, but are they actually required by regulation? As with many things in aviation, the answer to this question is “it depends.”

Strictly speaking, these things are not mandated by regulation for an aircraft operated under Part 91. Just because the manufacturer’s maintenance manual or service bulletin says that we “must” do such operations every so many months or so many hours doesn’t mean that we actually have to do it. Such things are truly mandatory only if they are required by an Airworthiness Directive or by an FAA-approved Airworthiness Limitation.

Nevertheless, if the shop doing an annual inspection on our airplane is a Repair Station, then they are compelled to follow the procedures in their FAA-approved Repair Station Manual. If the RSM says that they will do a full gear rigging every year or a magneto inspection every 500 hours, or that they will comply with all scheduled maintenance set forth in the aircraft manufacturer’s maintenance manual, then that’s what they are obliged to do as a condition of their Repair Station Certificate. If you don’t like it, you can always take your aircraft to another shop.

What if your annual inspection is being done by a shop that is not a Repair Station? The A&P/IA inspecting your airplane is not compelled by regulation to perform these procedures. But if he insists on doing them because he considers them essential to ensure that your aircraft is safe to fly, he’s still on pretty firm ground.

What “airworthy” means

AirworthyWhen an IA signs off an annual inspection, he’s asserting that the aircraft is airworthy.  For an aircraft to be “airworthy” it must meet two criteria: (1) it must be in compliance with its type design and all applicable airworthiness requirements (such as ADs), and (2) it must be in condition for safe operation.

Criterion #1—compliance with type design, ADs and other airworthiness requirements—is theoretically an objective standard. If you had a dozen IAs inspect an aircraft, they should all theoretically agree whether the aircraft is or is not in compliance.

However, criterion #2—being in condition for safe operation—calls for a subjective judgment by the IA.  Different IAs may reasonably differ on whether an aircraft is “in condition for safe operation” and there’s nothing wrong with that.

No IA can make a valid case that a complete gear rigging or 500-hour magneto maintenance is “required by regulation” on a Part 91 airplane.  However, the IA would be on firm ground if he took the position that both these procedures are essential to ensure that the aircraft is “in condition for safe operation.”

Any time a mechanic tells you that something is required by regulation, it’s perfectly appropriate for you to ask him to show you the specific regulatory reference that is the basis for his assertion.  In my experience, mechanics often say that something is required by regulation when in fact it isn’t required for Part 91 operators.

On the other hand, if a mechanic tells you that he is unwilling to approve an aircraft for return to service after an annual inspection unless certain work is done because he considers that work necessary to ensure that the aircraft is “in condition for safe operation,” he’s well within his rights.  The IA is required to make that determination at annual inspection, and his determination is subjective so it’s difficult to challenge.

What if an IA insists on something you consider excessive and unacceptable—e.g., requires removal of all cylinders at every annual, or is adamant that you major an apparently healthy engine just because it has reached TBO—because he considers it essential to satisfy himself that your aircraft is “in condition for safe operation”? If you don’t want the IA to do the work and can’t talk him out of it, then you really have only two options.

One option is not to let him do the inspection, and to take your airplane to another shop or mechanic with a more reasonable attitude.

The other option is to direct the unreasonable IA to complete the inspection without performing the disputed procedure, and sign off the annual with discrepancies. This means that you’ll get your airplane back with a signed and dated list of items the IA considers unairworthy. You can’t fly the airplane (unless you obtain a ferry permit), but you can take it to another mechanic (hopefully one with a more reasonable attitude) and ask him to resolve the discrepancies and approve the aircraft for return to service. The second mechanic only needs to deal with the listed discrepancies—he does not need to redo the annual inspection.

Shades of gray

Shades of GraySome would have you believe that airworthiness is a black-and-white concept: either something is airworthy or it isn’t. Not so.

The aspects of airworthiness concerned with determination of conformance to type design and airworthiness requirements are indeed black-and-white. Either a wing skin is made of the required .032”-thick 2024-T3 Alclad aluminum or it isn’t. Either AD 2000-01-16 has been complied with or it hasn’t.

However, the aspects of airworthiness concerned with determination of condition for safe operation are subjective and come in a thousand shades of gray. Different mechanics may reasonably differ on whether a landing gear really needs to be rigged at every annual, or whether mags really need to be disassembled every 500 hours, or flexible hoses changed every five years, or an engine overhauled when it reaches published TBO.

As an aircraft owner, you would be wise to interview a prospective IA and determine whether his philosophy about maintenance and airworthiness is compatible with your own before hiring him to perform an annual inspection on your aircraft. That goes double if you’re hiring a Repair Station.

Mike Busch is arguably the best-known A&P/IA in general aviation, honored by the FAA in 2008 as National Aviation Maintenance Technician of the Year. Mike is a 7,500-plus hour pilot and CFI, an aircraft owner for 45 years, a prolific aviation author, co-founder of AVweb, and presently heads a team of world-class GA maintenance experts at Savvy Aviation. Mike’s book Manifesto: A Revolutionary Approach to General Aviation Maintenance is available from Amazon.com in paperback and Kindle versions.

Misfueled!

Decals

Jet fuel contamination of avgas remains a killer.

On March 2, 2008, a turbonormalized Cirrus SR22 was destroyed when it crashed shortly after takeoff in Rio de Janiero, Brazil, killing all four people aboard. Shortly after the aircraft departed from runway 20, the airplane’s engine lost power, and the aircraft hit a building and exploded. Further investigation revealed that the aircraft had been refueled with Jet A instead of 100LL.

This report reminded me of an incident 16 years earlier during which my own 1979 Cessna T310R was misfueled with Jet A at San Carlos (Calif.) Airport, a busy GA airport just south of SFO. Fortunately, I caught the (mis)fueler in the act, red handed. Had I not been lucky enough to do that, I probably wouldn’t be writing this column.

Normally, I either fuel my aircraft myself (at a self-serve pump) or watch it being fueled (when avgas is supplied by truck). On this occasion, I’d radioed for the fuel truck and waited patiently for it to arrive. After 10 minutes of waiting, Mother Nature intervened and compelled me to walk into the terminal building in rather urgent search of a loo. By the time I took care of my pressing business and returned to the ramp, there was a fuel truck parked by my airplane and a lineperson pumping fuel into my right main tank.  As I approached the aircraft, I observed to my horror that the truck was labeled “JET A.”

Theoretically impossible

At first, I was not too worried, because I believed that misfueling my airplane with Jet A was physically impossible. That’s because in 1987 (the year I purchased by T310R), all turbocharged twin Cessnas became subject to Airworthiness Directive AD 87-21-02 which mandated installation of restrictor ports on all fuel filler openings. The restrictor ports were designed to make it impossible to insert an industry standard Jet A nozzle, while accommodating the smaller diameter avgas nozzle.

The AD was issued because the FAA became aware that a large number of misfueling indicents and accidents were occuring in turbocharged aircraft. These aircraft typically were prominentaly decorated by the factory with the word “Turbo” and apparently linepeople were confusing it with “Turbine” and pumping Jet A into the tanks.

So the FAA mandated that jet fuel trucks install a wide spade-shaped fuel nozzle, and that vulnerable airplanes (like turbocharged twin Cessna) have restrictor ports installed into which the wide jet fuel nozzle would not fit. This made misfueling of piston aircraft with jet fuel theoretically impossible. (They also said that it’s theoretically impossible for bumblebees to fly.)

But as I arrived at my airplane, I discovered that indeed my left main tank had been topped with Jet A. How was this possible? A subsequent investigation by the local FSDO revealed that the Jet A fuel truck at San Carlos Airport had not been fitted with the correct spade-type nozzle. (I suspect they got in trouble for that.)

Jet-A nozzle vs. avgas nozzle

Jet fuel nozzles have a wide spade top that is theoretically incapable of being inserted in an avgas fuel filler equipped with a restrictor ring—but don’t count on it!

Undoing the damage

I spent literally hours trying to find an A&P on the field that would assist me in purging the fuel system of its witches’ brew of 100LL and Jet A. That turned out to be surprisingly difficult. The fueling company was falling all overitself to be helpful (because I’m sure they feared a big lawsuit) but they had no mechanics or maintenance capabilities. There were several maintenance shops on the field, but none wanted to go near my contaminated airplane, clearly afraid of the potential liability exposure. Finally, I persuaded one maintenance manger to help me out after writing and signing an omnibus waiver absolving the shop and its mechanics of any liability in connection with their work on my aircraft.

The purging process itself was quite an eye opener. We drained the tanks as completely as possible, putting the noxious effluent into a 55-gallon drum provided by the fueling company (who had agreed to deal with the costly disposal of the nasty stuff). We disconnected the fuel line going to the engine-driven fuel pump and drained all the fuel from that as well.

Next, 5 gallons of 100LL (donated gratis by the fueling company) was poured into the main tank, and then pumped through the system using the electric boost pump and drained from the disconnected fuel line into a 5-gallon bucket.  The fuel in the bucket was tested for Jet A contamination using the paper-towel test: A few drops are placed on a paper towel and allowed to evaporate completely. Pure 100LL will not leave an oily ring on the towel, but even small amounts of Jet A contamination will leave an obvious ring. The stuff in the bucket flunked the test.

Another 5 gallons of 100LL were poured into the tank, and the process repeated. Once again, it flunked the paper-towel test. We had to repeat the procedure three more times before we were satisfied that the system was essentially kerosine-free. We reconnected the fuel line, cowled up the engine, the fueling company then topped off the airplane (again gratis), and I was finally good to go…fully six hours after the misfueling incident.

Restrictor filler & GATS jar

Be sure all your fuel filler ports have restrictor rings. The big GATS jar (available at Sportys, Aircraft Spruce, and elsewhere) does a far better job than the slim screwdriver-type testers.

Lessons learned

I learned some important lessons that day. Perhaps the most important is that it’s impossible to distinguish pure avgas and a mixture of avgas and Jet A by color alone. My main tanks had been about half-full of avgas, so after the misfueling they contained roughly a 50-50 mix. If you take a jar full of pure 100LL and another jar full of a 50-50 mix of 100LL and avgas, I guarantee you will not be able to see any difference in color or clarity between the two.

I hadn’t realized that before. I has always been taught that you sump the tanks and observe the color—100LL is blue and Jet A is straw color. What I was not taught is that a mixture of 100LL and Jet A is also blue and that you simply can’t tell the difference visually. In retrospect, I shudder to think what would have happened had I not caught that Jet A truck in front of my airplane.

I was also taught that since Jet A is significantly heavier than avgas (6.7 lbs/gal versus 5.85 lbs/gal), the Jet A and 100LL will separate just like oil and water, with the Jet A at the bottom (where the sump drain is) and the 100LL at the top. That’s true, but only if the contaminated fuel is allowed to sit for hours and hours. It turns out that 100LL and Jet A mix quite well, and the mixture takes a surprisingly long time to separate.

There are at least two good ways to distinguish pure 100LL from kerosine-contaminated 100LL. One is by odor: Jet A has a very distinctive odor that is detectable even in small concentrations. The other (and probably best) is by using the paper-towel test: Pour a sample on a paper towel (or even a sheet of white copy paper), let it evaporate, and see if it leaves an oily ring.

Nasty stuff

What effect does Jet A contamination have on a piston engine? Enough to ruin your day.

You can think of Jet A as being fuel with a zero octane rating. Any piston engine that tries to run on pure Jet A will go into instant destructive detonation. However, in real life, we almost never encounter that situation because the tanks (at least the main tank used for takeoff) is almost never completely dry when the aircraft is misfueled.

Therefore, the real-world problem is not running on pure Jet A, but on running on a mixture of 100LL and Jet A.  Depending on the mixture ratio of the two fuels, the effective octane rating can be anything between 0 and 100. A mixture with a lot of Jet A and just a little 100LL might be detectable during runup.  A 50-50 mix might not start to detonate until full power is applied, and the engine might fail 30 seconds or 3 minutes after takeoff. Just a little Jet A contamination might produce only moderate detonation that might not be noticed for hours or even weeks. Like so many other things in aviation, “it all depends.”

The Cirrus SR22 accident in Rio reminds us that the problem of misfueling is still with us, despite all the efforts of the FAA to eradicate it. We need to be vigilant. Always watch your airplane being fueled if you possibly can. Make sure its fuel filler ports are equipped with restrictor rings. Don’t just look at the fuel you drain from your sumps—sniff it, and when in doubt, pour it on a paper towel.

Mike Busch is arguably the best-known A&P/IA in general aviation, honored by the FAA in 2008 as National Aviation Maintenance Technician of the Year. Mike is a 7,500-plus hour pilot and CFI, an aircraft owner for 45 years, a prolific aviation author, co-founder of AVweb, and presently heads a team of world-class GA maintenance experts at Savvy Aviation. Mike’s book Manifesto: A Revolutionary Approach to General Aviation Maintenance is available from Amazon.com in paperback and Kindle versions.
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