Magazine Articles

If your certificated aircraft needs a replacement part that’s ridiculously expensive or downright unobtainable, the FAA will allow you to produce one yourself.  The 1960s and 1970s were the biggest years for production of piston GA airplanes. By the peak production year of 1979, manufacturers like Beech, Cessna, Mooney, Piper, and others were pushing new airplanes out the door as fast as they could, and owners were snapping up all they could produce. All this came to a crashing halt in the early 80s, when the effects of a double-dip recession were magnified by passage of massive tax reforms that eliminated financial incentives to buy new airplanes. Piston GA manufacturing all but ceased altogether, and it has never really recovered. It’s no surprise, then, that most of the piston GA aircraft flying today are between 30 and 50 years old. Keeping these aircraft flying is becoming more challenging every year, particularly with respect to finding replacement parts. Some manufacturers—notably Cessna—continue to do a far better job of keeping replacement parts available for these decades-old, out-of-production aircraft than we have any right to expect. Some other manufacturers (who shall remain nameless) don’t support their legacy aircraft nearly as well. Many parts […]

Sensitive and fragile compared to their automotive brethren, aircraft batteries need TLC if you don’t want to be left stranded. Aircraft batteries are the Rodney Dangerfields of general aviation. They get no respect. We let them sit unflown for weeks at a time, sometimes months. We deep-discharge them by forgetting to turn off the master switch. Then we jump-start the airplane with a ground power unit and go fly as our alternator fries them with excessive charging current. We fail to check our bus voltage regularly, resulting in long periods of undercharge or overcharge. If we’re lucky, the electrolyte level gets checked once a year at annual inspection time. Then we cuss them out when the airplane won’t start on a cold Sunday winter morning in Sheepdip, Nebraska, and there’s no mechanic or battery cart on the field. Not Die-Hards We probably learned these bad habits from our experience with automobiles. Car batteries are big, heavy, robust brutes that can tolerate this sort of abuse. Aircraft batteries aren’t and can’t. They’re fragile and sensitive. They’re not Die-Hards. Aircraft batteries are built to be lightweight and compact. They have a small fraction of the capacity of our automotive batteries—typically 10-35 ampere-hours […]

We often treat the words “safe” and “airworthy” as if they were synonyms. They’re not.  On the landing roll, something didn’t feel right. The Cessna pulled strongly to the left. The pilot had to apply full right pedal and some right brake to keep it on the runway. As the pilot struggled to make the turnoff, it became clear what was wrong: The left main landing gear tire was flat. Naturally, this happened away from home base while the pilot was stopping for fuel and lunch in the middle of an important trip. (Doesn’t it always?) The pilot needed to get his airplane fixed and back in the air as quickly as possible. He contacted the local shop on the field—one he wasn’t familiar with—and asked them to recover his aircraft and fix the flat tire. The mechanic said that he had a new tire in stock for $200 and a tube for $50. Labor was estimated at two hours at a shop rate of $85/hour. It looked like this $100 hamburger would turn into a $500 hamburger. Having few options, the aircraft owner approved the work and asked the mechanic to use his best efforts to complete it quickly […]

How to ensure that nothing is coming apart inside your crankcase.  I’d been working with a Bonanza owner in Memphis for several weeks helping him chase down a problem with his Lycoming engine. Yes, Lycoming—the aircraft was an A36 with a Machen conversion to a fire-breathing 350 hp Lycoming TIO-540-J2BD engine. The owner of this hot-rod Bonanza initially reported that the engine had exhibited several episodes of rough running after startup, but that the engine seemed to run smoothly once it warmed up. The owner emailed me a data dump from his JPI engine monitor, which confirmed my suspicions that his “morning sickness” was caused by a couple of sticky exhaust valves in cylinders #4 and #5. Sticking exhaust valves is a fairly common malady in Lycomings, which is why Lycoming Service Bulletin 388C and Service Instruction 1481A call for doing a “valve wobble test” every 400 or 1000 hours (depending on what kind of exhaust valve guides are installed). The owner wound up taking his sick engine to an excellent engine shop near Memphis. The shop pulled the rocker covers and found the #4 exhaust valve springs black with carbon from a badly leaking exhaust valve guide. #5 had […]

Contrary to popular belief, more maintenance isn’t necessarily better. Often it’s worse—a lesson that was learned during WWII. I’ve written at length in prior issues of EAA Sport Aviation on the subject of Reliability-Centered Maintenance (RCM), the scientific and engineering discipline of designing optimum maintenance programs to provide the highest levels of safety and reliability at the lowest cost. RCM originated in the late 1960s from the work of Stanley Nowlan and Howard Heap at United Airlines, and quickly became the “bible” for how maintenance was done throughout the air transport industry. RCM was adopted by the U.S. military beginning in the mid-1970s, by the U.S. commercial nuclear power industry in the 1980s, and by many other industries in the 1990s. Today, RCM is the way maintenance is done in all segments of aviation except one: general aviation. Actually, RCM is now being widely adopted in high-end GA—at the Citation X, Gulfstream, Challenger and Global Express level—but not yet at the low end of the aviation food chain where most of us hang out. (One of my missions is to change that.) RCM Principles Fifty years ago, in the 1960s (when I first became a pilot and aircraft owner), aviation […]

What aircraft owners should know about piston aircraft engine oil. This is the first of a two-part article about the lubricating oil we use in our piston aircraft engines, and we’ll be covering a lot of territory. We’ll discuss the various types of engine oil—monograde versus multigrade, mineral oil versus synthetic—and the pros and cons of each. We’ll talk about aftermarket oil additives and whether they’re beneficial or just hype. We’ll touch upon oil consumption, optimum oil level, and how often to change the oil. We’ll also address oil filter inspection and spectrographic oil analysis, and how we use them to assess engine health. Six Key Functions If I asked you to explain the purpose of engine oil, I imagine you’d probably say something like “to lubricate moving parts and reduce friction and wear.” Now that’s certainly correct as far as it goes, but lubrication is only one of six key functions that oil must perform in your piston aircraft engine. In fact, the lubrication needs of our big displacement, slow-turning piston aircraft engines are really quite modest, compared for example to the high-revving engines in our automobiles. Lubrication demands tend to vary with the square of RPM, so a […]

You’ve been doing mag checks since your first flight lesson, but are you doing them right? From your first days as a student pilot, you were undoubtedly taught to perform a “mag check” as part of each pre-takeoff runup. But do you know how to do it correctly, what to look for, and how to interpret the results? Surprisingly, many pilots don’t. To begin with, most Pilot Operating Handbooks tell you to note the RPM drop when you switch from both mags to just one, and give some maximum acceptable RPM drop and sometimes some maximum acceptable RPM difference between the two mags. For example, the POH for my TCM-powered Cessna T310R specifies that an RPM drop more than 150 RPM on either mag or a difference more than 50 RPM between the two mags is unacceptable. Many Lycoming-powered aircraft specify a maximum drop of 175 RPM and a maximum difference of 50 RPM. Lycoming’s revised guidance on mag checks On June 18, 2010, Lycoming issued Service Instruction No. 1132B revising its guidance on how pre-flight mag checks should be performed. Some highlights of this new service bulletin: The entire revised Service Instruction 1132B may be found online at http://www.lycoming.textron.com/support/publications/service-instructions/pdfs/SI1132B.pdf EGT […]

Mechanics approve an aircraft for return to service after maintenance by signing a logbook entry, but pilots actually return the aircraft to service by flying it. Never forget that on the first flight after maintenance, you’re a test pilot…so please act accordingly. For months, a client of mine had been searching for a Bonanza A36 to buy. He’d narrowed his search to two very promising candidates. One of them had recently suffered a “forgot to remove the tow bar” prop strike. This necessitated an engine teardown inspection and prop overhaul, both paid for by insurance. The seller was appropriately upbeat in his communications with my client: The engine in the plane was torn down and no damage that was a result of the tow bar incident was present.  I’ve included the log book entries for the tear down and the final entry for the annual.   While this tow bar event has been a royal pain in the rear, we have ultimately ended up with a greatly upgraded plane and one that the buyer can have a extremely high level of understanding and confidence of the condition of the engine at 1,237 hours (like no other plane on the market).  A […]

Pilots still seem to have a lot of misconceptions about EGT. Let’s see if we can clear some of them up. These days, pilots of piston-powered aircraft seem to be fixated upon exhaust gas temperature (EGT). Scarcely a day goes by that I don’t receive a phone call or email or support ticket asking some EGT-related question. Pilots will send me a list of EGT readings for each of their cylinders and ask me if I think they look okay, whether I think their EGTs are too high, what maximum EGT limit I recommend, why their EGTs seem to be higher in the winter than in the summer, or why the EGTs on their 1972 Cessna 182 are so much higher than the ones on their friend’s 1977 model. They’ll voice concern that the individual cylinders on their engine have such diverse EGT readings, worry that the spread between the highest and lowest EGT is excessive, and ask for advice on how to bring them closer together. They’ll complain that they are unable to transition from rich-of-peak (ROP) to lean-of-peak (LOP) operation without producing EGTs that are unacceptably high. Each of these questions reveals a fundamental misunderstanding of what EGT […]

Destructive detonation and pre-ignition events can destroy your engine in two minutes flat. Know the symptoms, and act fast! At least once a year, I am contacted by an aircraft owner whose piston aircraft engine was destroyed or severely damaged by a destructive detonation or pre-ignition event. But lately, the pace seems to be quickening. In a recent 12-month period, I’ve encountered three of them. One recent incident involved Cirrus SR-20 powered by a 200 horsepower TCM IO-360-ES engine. The plane was equipped with a snazzy Avidyne Entegra MFD with an integrated engine monitoring system called “EMAX.” The CHT data downloaded from the EMAX system tells the short tale of this engine’s demise: Everything looked fine until about two minutes after the pilot applied takeoff power, at which point the #1 cylinder’s CHT began to climb rapidly compared to the other five cylinders. At the three-minute mark after brake release—with the aircraft at roughly 2,000’ AGL—CHT #1 rose above 400°F and set off a high-CHT alarm on the MFD. CHT #1 continued its rapid rise—nearly 1°F per second—that continued unabated until the piston and cylinder head were destroyed approximately five minutes after takeoff power was applied and two minutes after […]

We have the technology to prevent these failures by detecting them in the incipient phase. Last month we discussed how exhaust valves fail and why they sometimes fail prematurely. This month, we’ll shift our focus to how we can monitor exhaust valve condition, detect incipient valve problems, and deal with them before in-flight failure occurs. I started last month’s column with a description and photos of an in-flight exhaust valve failure that occurred in my airplane nearly 20 years ago. That failure occurred “back in the bad old days” before we had the sophisticated engine monitoring tools that we have today—specifically spectrographic oil analysis, borescope inspections, and digital engine monitors. Nowadays, there’s no excuse for such an in-flight failure because we have the technology to detect these problems early. Anyone who experiences an in-flight exhaust valve failure today just wasn’t paying attention. Borescope Inspections In my opinion, regular borescope inspections should be our first line of defense against exhaust valve failure. The borescope is an optical probe (see Fig. 4) or a subminiature digital camera (depending on which model is used) that can be inserted through a spark plug boss (usually the top one). It is used to perform a […]

Exhaust valves are the most heat-stressed components in your piston aircraft engine, and the most likely to fail prior to TBO. Here’s what you need to know about them. I experienced my first in-flight exhaust valve failure about twenty years ago. The engine started running very rough (as you might expect of a six-cylinder engine that was only running on five cylinders). After I landed, I noticed that the manifold pressure at idle was several inches higher than normal, confirming that something was definitely wrong with the engine. I put the airplane in the hangar, removed the top cowling and the top spark plugs, and performed a differential compression test. Five of the cylinders measured just fine, but one measured 0/80 with a hurricane of air blowing out the exhaust pipe. It was pretty obvious that this jug was going to have to come off. Once I wrestled the cylinder off the engine and looked at the exhaust valve, it was pretty obvious that something was missing (see Fig. 1). A fragment of the exhaust valve face had broken off and departed the premises for parts unknown. Luckily, it opted to depart through the wastegate and to spare the turbocharger […]

Your maintenance shop’s paperwork can make all the difference between a good outcome and a nightmare. When he contacted me, the owner of a pristine turbonormalized A36 Bonanza seemed obviously frustrated: I manage to fly only 50 to 75 hours a year, but my annual inspections have been running between $8,000 and $12,000 every year despite my low flying time. I think my mechanic is very honest and thorough, but I think he spends about 100 hours doing the inspection. Perhaps he is overdoing it? I asked the owner to fax me his invoices from this shop for the past two years so I could review them. He did, and when I reviewed the invoices, I found them profoundly disturbing.  It wasn’t just the totals that bothered me—about $7,000 for the 2008 annual and more than $12,500 for the 2009 annual—but the obscure, perhaps even intentionally cryptic nature of the invoices that made them almost impossible to evaluate. I’ve been looking at maintenance invoices for more than two decades, but these were perhaps the most inscrutable I’ve ever encountered. Let me show you what I mean: This invoice contains an astonishingly detailed description of the work performed that goes on […]

Every pilot understands the notion of “pilot in command.” That’s because we all had some certificated flight instructor (CFI) who mercilessly pounded this essential concept into our heads throughout our pilot training. Hopefully, it stuck. As pilot-in-command (PIC), we are directly responsible for, and the final authority as to, the operation of our aircraft and the safety of our flight. Our command authority so absolute that in the event of an in-flight emergency, the FAA authorizes the PIC to deviate from any rule or regulation to the extent necessary to deal with that emergency. (14 CFR §91.3) In four and a half decades of flying, I’ve overheard quite a few pilots dealing with in-flight emergencies, and have dealt with a few myself. It makes me proud to hear a fellow pilot who takes command of the situation and deals with the emergency decisively. Such decisiveness is “the right stuff” of which PICs are made, and what sets us apart from non-pilots. Conversely, it invariably saddens me to hear a frightened pilot abdicate his PIC authority by throwing himself on the mercy of some faceless air traffic controller or flight service specialist to bail him out of trouble. How pathetic! The […]

How do we assess whether a piston aircraft engine is airworthy? Compression tests and oil consumption are only part of the story—a smaller part than most owners and mechanics think. My friend Bob Moseley is far too humble to call himself a guru, but he knows as much about piston aircraft engines as anyone I’ve ever met. That’s not surprising, because the man has been rebuilding Continental and Lycoming engines for the four decades, so there’s not much about these engines that he hasn’t seen, done, and learned. From 1993 and 1998, “Mose” (as his friends call him) worked for TCM as a field technical representative covering Missouri, Kansas, Iowa, Nebraska, North and South Dakota, Minnesota, and the portion of Canada north of those states. “Then I made someone at the factory mad,” he says, “so they gave me Arkansas.” (Not really, but it always gets a laugh.) These days, Mose and his wife Rita operate a small shop called SkyTEK Inc. located at Fulton, Missouri, about 100 miles west of St. Louis. [http://www.skytekonline.com/] The company offers a wide variety of engine-related services including custom overhauls, prop strike inspections, cylinder work, accessory repairs, fuel injection system setup, and all manner […]

By Mike Busch To apply RCM principles properly to the maintenance of our piston aircraft engines, we need to analyze the failure modes and failure consequences of each major component part of those engines. Last month, we looked at the issue of catastrophic failures of piston aircraft engines, and saw that the predominant risk of such failures is greatest when the engine is young, not when it’s old. This month, we’ll examine the critical components of these engines, how they fail, what the consequences of those failures have on engine operation and safety of flight, and what sort of maintenance actions we can take to deal with those failures effectively and cost-efficiently. Crankshaft It’s hard to think of a more serious piston engine failure mode than a crankshaft failure. If it fails, the engine quits. Yet crankshafts are rarely replaced at overhaul. Lycoming says their crankshafts often remain in service for more than 14,000 hours and 50 years! TCM hasn’t published this sort of data, but TCM crankshafts probably have similar longevity. Crankshafts fail in three ways: (1) infant-mortality failures due to improper material or manufacture; (2) failures following unreported prop strikes; and (3) failures secondary to oil starvation and/or […]

Last month, we examined the principles of RCM used by the airlines and military to achieve cost-effective maintenance. Now, let’s explore how RCM can be applied to our small GA aircraft, and especially to our piston aircraft engines. For three decades, the airlines and military have been using Reliability-Centered Maintenance to slash maintenance cost and improve reliability. Most of these benefits have come from replacing fixed overhaul intervals with on-condition maintenance. Unfortunately, RCM has not trickled down to the low end of the aviation food chain. Maintenance of piston GA aircraft remains largely time-directed rather than condition-directed. Most GA owners dutifully overhaul their engine at TBO, overhaul their prop every 5 to 7 years, and replace their alternators and vacuum pumps every 500 hours, just as Lycoming, TCM, Hartzell, McCauley, Kelly Aerospace and Parker-Hannifin recommend. Bonanza owners have their wing bolts pulled every 5 years. Cirrus owners replace their batteries every 2 years. And the beat goes on… Does any of this make sense? After analyzing reams of operational data from a number of major air carriers, RCM researchers concluded that fixed-interval overhaul or replacement rarely improves safety or reliability, and often makes things worse. When does TBO make sense? […]

A strategy known as “Reliability-Centered Maintenance” has drastically reduced the cost of maintaining transport and military aircraft, while simultaneously improving dispatch reliability. Isn’t it time we applied this approach to piston GA? More than 30 years ago, in 1974, the U.S. Department of Defense commissioned United Airlines to prepare a report on the techniques used by the airline industry to develop cost-efficient maintenance programs for civil airliners. The resulting report, titled Reliability-Centered Maintenance [F. S. Nowlan & H. Heap, National Technical Information Service, 1978] described a radically different approach to aircraft maintenance, based on rigorous analysis of traditional maintenance practices and evaluation of their shortcomings. Traditionally, a major emphasis of aircraft maintenance programs had been defining specific overhaul and retirement intervals (TBOs) in order to achieve a satisfactory level of reliability. However, engineering analysis of reams of operational data from a number of major air carriers produced fascinating insights into the conditions that must exist for scheduled maintenance to be effective. Two discoveries were especially surprising: For example, RCM researchers determined back in the 1970s that scheduled overhauls on turbine engines do not produce any reliability or economic benefit, and that maintaining such powerplants strictly on-condition provides longer life, reduced […]