Magazine Articles

Chasing down an elusive charging system gremlin Intermittent problems are the worst! They always seem to happen at the worst possible time, like when you’re in the middle of nowhere away from home base. They never seem to happen when you want them to happen, like when you’re trying to show them to your A&P so he can troubleshoot and fix them.  Case in point: Nearly 30 years ago, not long after I bought my Cessna 310. I was in the middle of a 4,000-mile cross-country that took me from California to Illinois, Kansas, Oklahoma, and back home to California. I was not an A&P at the time, simply a maintenance-involved airplane owner. (The A&P would come a decade later.) The first sign of trouble occurred as I was starting engines at Champaign, Illinois headed for Wichita. With both engines running, I noted that the amber warning light marked “ALT FAILURE: R ALT” did not go out the way it should have. I didn’t know whether this was a genuine alternator failure or just a malfunctioning idiot light, but figured I’d better try to find out.  I shut off the known good alternator (the left one) to see what would […]

How often does your propeller REALLY need to get overhauled? “Your prop is due for overhaul,” says your IA who you hired to do your annual inspection. “It’s been six years.” If your airplane has a constant-speed prop, overhauling it is going to set you back about $3,000 including removal and installation labor.  If it has deice boots, figure another $1,000. If you fly a twin like mine with two full-feathering constant-speed deiced props, well…ouch! Nowadays most props have a TBO of 2000 or 2400 hours and 60 or 72 months, whichever comes first. Doing the math, you’d have to average more than 400 hours per year for the 2000 or 2400 hours to come first. For most of us, it’s the calendar time component of the TBO that always comes up first. The average owner-flown GA airplane flies roughly 100 hours a year, which means that the prop will come “due” for overhaul after just 500 or 600 hours. If you fly less than 100 hours a year, it’s even worse. Do we really have to overhaul our props every five or six years regardless of how few hours are on them? Does it even make sense to do […]

What to do about uncomfortably high CHT For decades now, I’ve been preaching that the two keys to piston aircraft engine longevity are avoiding extended periods of disuse and managing CHT. If you allow your engine to sit unflown for weeks at a time, you risk internal corrosion—and corrosion is the number one reason that engines fail to make TBO. If you allow your CHTs to get too hot, you increase the stress on the engine’s reciprocating components (especially connecting rod bearings and bushings, piston pins, and valves), and increase the risk of catastrophic failure from destructive detonation, preignition, and head-to-barrel separation. In a perfect word, we would have sensors in each of our cylinders measuring peak combustion chamber pressure and instrumentation that would let us see this in the cockpit. This is exactly the way engines are instrumented when they run on GAMI’s engine test stand in Ada, Oklahoma—the most sophisticated piston aircraft engine test facility in the world. But it’s not practical to install this sort of instrumentation in our aircraft, so CHT is the best proxy for internal cylinder pressure (ICP) that we have. If we want to protect our engines against excessive ICP, we need to […]

This cutting-edge technology could revolutionize GA maintenance. The exhaust valve is the most likely component of a piston aircraft engine to fail catastrophically. When one fails, combustion ceases in the cylinder, the engine loses power and starts running rough. This usually results in a precautionary landing—on-airport if you’re lucky, off-airport if you’re not. It’s particularly serious with a four-cylinder engine, because a four runs a lot worse on three than a six does on five. Occasionally, the liberated valve fragment gets wedged into the piston crown, which can shatter the piston and cause a total power loss, sometimes with fatal results. That’s why it’s so important to detect incipient exhaust valve failures early before they can cause serious problems. The traditional way is the annual compression test, but that isn’t a very reliable method because loss-of-compression typically doesn’t occur until the valve is very sick and close to failing.  A borescope inspection is vastly better and can detect failing valves a lot earlier. AOPA publishes a great poster to help mechanics understand what to look for—Google “Anatomy of an Exhaust Valve Failure.” Unfortunately, most shops don’t do regular borescope inspections, and the ones that do typically do them only at […]

If your A&P seems over-cautious and self-protective, there’s good reason. By Mike Busch Mechanics have always been subject to FAA sanctions: certificate suspension or revocation, fines, warning notices, letters of correction, and remedial training. But enforcement actions against GA mechanics were exceedingly rare. The most common way for a mechanic to run afoul of the FAA is to “pencil whip” a logbook entry—for example, stating that some Airworthiness Directive (AD) was complied with or some other inspection or repair was performed—and then the FAA finds that the work wasn’t actually done as documented. If a mechanic is caught “autographing a lie” by the FAA, his certificates are probably toast. That said, it’s pretty easy for mechanics to avoid getting crossways with the FAA. The regulations that govern mechanics (Part 43) are far more concise and understandable than those that govern pilots and aircraft owners (Parts 91). Part 43 contains just 13 rules and they’re remarkably straightforward. Reduced to its essentials, Part 43 simply requires that a mechanic: Pretty commonsense stuff. A mechanic who makes a good-faith effort to follow these simple rules is unlikely to get hassled by the Friendlies. Civil Liability But an A&P who complies with these regs […]

When piston airplanes are fueled with Jet A, bad things can happen. 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. On April 17, 2015, a Cessna 421B crash-landed on a highway shortly after takeoff from Lufkin, Texas, resulting in one serious and two minor injuries. According to the pilot, the aircraft seemed to perform normally during the runup, takeoff and initial climb. Passing 2,100 feet AGL, the left engine sputtered and lost all power. Within 30 seconds, the right engine also lost all power and the big cabin-class twin descended for a forced landing. The airplane landed hard, damaging the wings and fuselage and rupturing the right fuel tank, finally coming to rest in the grassy median of a highway. The smell of jer fuel was prominent at the accident scene. Investigators found that the FBO’s Jet A truck had recently had its wide duckbill-style nozzle […]

Lessons learned from geriatric engines. Time Between Overhaul (TBO) is a strange concept. The FAA, in its infinite wisdom, requires aircraft engine manufacturers to publish TBOs for their engines, but doesn’t require aircraft owners to abide by them. You are free to continue flying behind your engine as it remains airworthy.  Yet many owners and mechanics start getting nervous as they see tach time approach published TBO. Countless numbers of healthy engines are needlessly euthanized when their time-in-service approaches that consecrated number. For Part 91 operators, doing so is not an FAA requirement—it’s more like a religious belief. My Teachable Moment teach·a·ble mo·mentnoun(U.S.) an event or experience which presents a good opportunity for learning something about a particular aspect of life. [Oxford English Dictionary] My teachable moment that convinced me to stop believing in overhauling at TBO came about 30 years ago. In 1987, I purchased a Cessna 310 twin whose two TSIO-520 engines were just 100 hours shy of Continental’s published TBO of 1,400 hours. It didn’t take long for me to get there. When I did, I asked for advice from several friends who were veteran A&P/IAs. (This was long before I was an A&P myself.) Their unanimous […]

Thoughts on finding a good purchase candidate An extraordinary number of GA airplanes were bought and sold in 2020. I imagine this was somehow related to the pandemic, although I’m not sure exactly how. What I do know is that my company had been averaging about 10 prebuys per month in 2019, but by the summer of 2020 we were doing 50 prebuys per month. As I write this part way into 2021, the rate has gradually dropped back to about 30 per month, which is still much higher than it used to be. A significant number of these are first-time airplane buyers. They go online to sites like Aircraft Shopper Online, Controller, and Trade-A-Plane Online and are confronted with an overwhelming number of possible purchase candidates. Many come to me asking for help in how to narrow the field down to a few. Single or twin? Retractable or fixed gear? High wing or low wing? High-time or low-time engine or airframe?  What’s Your Mission? When I’m approached for advice by a prospective buyer, my first question is generally, “How do you plan to use this airplane? What’s your typical mission?” Is the aircraft going to be used primarily for […]

What happens when an owner and an IA can’t agree? By Mike Busch Sam is a pilot, engineer and serial entrepreneur who lives near Washington DC. About 10 years ago, he bought a 1966 Cessna 182J Skylane that is based and maintained in nearby Maryland. It’s been a pretty economical airplane to operate and maintain. Sam’s IA charges a flat-rate of $1,200 for the annual inspection, and Sam told me that “I’ve never paid more than $3,300 for an annual inspection plus repairs.” About a year ago, Sam flew his airplane to the West Coast on business. While there, the Skylane’s annual inspection came due. Sam decided to take his plane to a well-known California shop—let’s call it “Alpha Aviation”—for the inspection. Because of the airplane’s benign maintenance history, Sam didn’t anticipate any big surprises.  Imagine his shock when Alpha Aviation sent him an 11-page preliminary discrepancy list itemizing 63 discrepancies, 40 of which were identified as “affecting airworthiness status.” Inspection Findings Ten of the 40 airworthiness discrepancies involved compliance with Airworthiness Directives. Some of these were routine recurrent inspections—seat tracks, ignition switch, oil filter adapter, fuel filler caps, flap actuator jackscrew—that would be expected in any Cessna 182 annual […]

An FAA review of 10 years of NTSB data tries to quantify the risk. I’ve been known preach about the virtues of maintenance minimalism—a.k.a. “if it ain’t broke, don’t fix it”—and the risk of maintenance-induced failures—a.k.a. “MIFs.” But just how risky is maintenance? How often to MIFs occur? How serious are the consequences when they do? When asked these questions, I usually lick my finger, hold it up in the breeze, and say that roughly three-quarters of GA accidents are pilot-caused and one-quarter are machine-caused. Licking again, I say that of the machine-caused ones, roughly half are mechanic-caused (i.e., MIFs). That would put the fraction of GA accidents caused by MIFs at around one-eighth give or take a few spitballs. While cleaning out my office recently and rummaging through stacks of old papers (most of which I threw in the trash), I ran into an old FAA study that might shed a little more light on this subject, and help quantify the risk of maintenance more accurately than my aforementioned spit balling. Published in December 2002, the FAA study titled General Aviation Maintenance-Related Accidents: A Review of Ten Years of NTSB Data analyzed NTSB accident investigation reports involving GA accidents […]

Preventing and dealing with magneto-ignition system failure. Both the FARs and their predecessor CARs require that certificated spark-ignition recip-rocating aircraft engines—the kind most of us fly behind—have fully redundant dual ignition systems: PART 33—AIRWORTHINESS STANDARDS: AIRCRAFT ENGINESSubpart C—Design and Construction; Reciprocating Aircraft Engines§ 33.37   Ignition system. Each spark ignition engine must have a dual ignition system with at least two spark plugs for each cylinder and two separate electric circuits with separate sources of electrical energy, or have an ignition system of equivalent in-flight reliability. There’s a good reason for this: Ignition system failures are relatively commonplace. Without a properly functioning ignition system, the engine could quit, the airplane could fall out of the sky, and people could get hurt. How often do ignition systems fail? Well, spark plug failures happen a lot, but the consequences aren’t usually serious—usually they’re not even noticeable—precisely because we have two spark plugs in each cylinder, and one is enough to keep the cylinder producing power. Usually, the only sign that a spark plug has failed in-flight is that the EGT on the affected cylinder rises by 50°F or so. Unless you have an engine monitor installed and keep it in “normalize mode” […]

The spark plugs in most piston aircraft engines are still powered by 120-year-old technology. My airplane’s piston engines utilize a magneto ignition system. If you’re flying a certificated airplane, chances are good that yours does, too. The fact that we’re still stuck with these superannuated mechanical black boxes is a testament to just how hard it is to get modern technology FAA-certified. Magneto ignition first appeared on the 1899 Daimler automobiles, and high-voltage magnetos were introduced by Bosch in 1903. Mags were largely abandoned in autos in the 1920s in favor of battery-powered ignition.  Electronic ignition systems (EIS) are almost universally used on experimental amateur-built aircraft but are still quite rare on certificated airplanes thanks to FAR Part 33 (“Airworthiness Standards: Aircraft Engines”) which remains firmly routed in the Dark Ages. The S-1200 magnetos on my airplane are essentially indistinguishable from the ones that Bendix built in the 1940s. Since so many of us are still flying behind these archaic “tractor mags” it’s probably a good idea for us to understand how they work. A high-voltage magneto is a self-contained ignition system that converts mechanical rotation into high-voltage pulses that are used to fire the spark plugs and does so […]

Rigid baffles and flexible baffle seals are critical in keeping your engine cool. The Cessna T210 owner was clearly frustrated with his new engine installation: “I recently had my engine rebuilt and had a new baffle kit installed. The CHTs for cylinders #5 and #6 are always 20ºF to 30ºF hotter than the rest. During climb the difference gets even bigger. Cylinder #5 and #6 CHTs are very difficult to keep below 400ºF during a climb, even with the cowl flaps open and full-rich mixture. Should I consider giving them some air? On cylinder #6, why not cut one or more holes in the white aluminum baffle in front of the cylinder? On cylinder #5, why not drill one or more holes in the horizontal aluminum plate located behind the oil cooler?” After looking at the marked-up photo from the T210 owner, I replied that cutting holes in the baffles was definitely NOT a good idea, and that doing so would undoubtedly make the cooling problems worse, not better. It was apparent that this owner didn’t understand how the powerplant cooling system in his aircraft works, or what the function of the baffles is. He’s not alone—some A&P mechanics don’t […]

Maintenance-induced problems are common, and it often an experienced pair of eyes to diagnose them. Elko Regional Airport (KEKO) is located in northeast Nevada at an elevation of 5,000 feet above sea level, and is known for its competitive avgas prices. It’s pretty much in the middle of nowhere…but if you happen to be flying from the Pacific Northwest to Arizona, KEKO is a convenient midway fuel stop. That’s exactly what Jack was doing one fine Thursday afternoon in his Cirrus SR22 Turbo. The airplane had been performing flawlessly, so after landing at Elko Jack was floored to find engine oil dripping out of the left exhaust stack and streaked along the left underside of the fuselage. This is not the sort of thing that you want to see when you’re in the middle of nowhere. Jack checked with the FBO but their A&P had gone home for the day. He phoned Savvy Aviation’s 24/7 hotline number and quickly got a callback from Tony Barrell A&P/IA, one of Savvy’s most experienced account managers and former director of maintenance at a large Cirrus Service Center. Remote Diagnosis Jack sent Tony several smartphone photos of his oil-covered airplane. “No mechanic is available […]

There’s a lot more to piston aircraft engine oil than you might think When it comes to piston aircraft engines, the role of engine oil is complicated. It lubricates moving parts to reduce friction and wear, but that’s only one of six key functions it performs, and perhaps not even the most important one. The lubrication requirements of slow-turning direct-drive Continentals and Lycomings that most of us fly behind are really quite modest compared to the high-revving engines in our automobiles. Lubrication demands tend to vary with the square of RPM, so a car engine with a 7000 RPM redline has vastly more demanding lubrication requirements than an aircraft engine with a 2700 RPM redline does. Lubrication vs. Friction & Wear Friction occurs because even the smoothest metal surfaces have microscopic peaks and valleys known as asperities. Whenever surfaces come in contact, these asperities adhere to one another via tiny micro-welds. If those surfaces are in relative motion, the micro-welds constantly fracture and re-form, resulting in friction and wear. Friction is the resistance to relative motion and wear is the loss of material. Both are due to the fracture of the micro-welds. The purpose of lubrication is to reduce friction […]

What if your airplane breaks and there’s no one to fix it? Being a dyed-in-the-wool technology freak, I drive a Tesla Model 3. It has been a superbly reliable vehicle that doesn’t require maintenance very often. But when it does, I take my Tesla to the nearest Tesla dealership, where it is worked on by factory-trained mechanics who work on nothing but Teslas all day long and know them like the backs of their hands. The situation was very similar in 1968 when I bought my first airplane, a brand new 1968 Cessna 182 Skylane. I based it at what is now called “John Wayne Airport” in Santa Ana, California. In those days, there were three big aircraft dealerships on the field: a Cessna dealer, a Piper dealer, and a Beechcraft dealer.  When my Skylane needed maintenance ,I took it to the Cessna dealership on the field who employed a half-dozen factory-trained A&Ps who worked on nothing but single-engine Cessnas all day long and knew them like the backs of their hands. The Cessna dealership also had a parts room to die for, so when my airplane needed some component to be replaced it was likely to be in stock. […]

Why it’s no substitute for a proper independent prebuy. Every month I receive hundreds of emails from aircraft owners seeking advice or assistance. For the most part, I genuinely enjoy these interactions and the opportunity to help fellow aircraft owners.  Occasionally, however, I run into something that I find deeply disturbing. That was the case with a message I received recently from a 60-hour student pilot—let’s call him Dan—who had just purchased his first airplane in Texas and flown it back home to California accompanied by his flight instructor. The aircraft in question was a 1974 Piper Warrior PA-28-151. “Part of my deal with the previous owner was that he would have a complete annual inspection performed and any airworthy discrepancies corrected before I took delivery,” Dan said in his email. “The annual was completed with no squawks in mid-February and I flew it back from Texas in early March.” “The airplane seemed okay on the ferry flight to California,” Dan continued, “except for the rate-of-climb which was averaging only 300-500 feet per minute. I guess we didn’t really notice it since all the airports we used had long runways. But after getting it back to my home field in […]

…and how you can avoid engine damage and power loss if you know the answer. If you fly behind a Continental or Lycoming, each of your engine’s cylinders has two valves, intake and exhaust. The valves open and close by sliding in and out through close-tolerance tubes called valve guides that are press-fit into the cylinder heads. The valves are opened by a valve train consisting of a cam lobe, a lifter (tappet), a pushrod, and a rocker arm. They are closed by a pair of strong concentric valve springs. A sticking or stuck valve is one that no longer slides smoothly in and out through its valve guide. This can happen when there is a build-up of deposits on the valve stem and/or inside the valve guide. Of course, you knew all that. What you might not know is what these deposits are made of (it’s not carbon), what causes them to form (it’s not heat), what happens when they do (it’s not pleasant), and how you can prevent this from happening (it’s not hard). Morning Sickness and Worse If the valve guide isn’t excessively worn, there’s not much clearance between the guide and the valve stem. The clearance […]

When it comes to GA crashes, the NTSB doesn’t always get it right, nor does the jury In December of 2012, a father and his son arrived at the airport to pick up the father’s Cessna 421C cabin-class piston twin, which had been in the maintenance shop for months receiving a new paint job and an annual inspection. Both father and son were experienced multiengine pilots.  The son had earlier flown the aircraft on an hour-long post-maintenance test flight with a mechanic in the right seat. The test flight revealed that the left engine’s RPM was 100 RPM over red-line and its fuel flow was a couple of gallons per hour low. After landing, the mechanic made adjustments to the left engine’s RPM and fuel flow and corrected a few minor cosmetic issues. The plan was for the son to fly the aircraft to a nearby airport that was its home base, and for his dad to drive to meet him there. The pilot ran up the engines on the ramp in front of the shop for several minutes before taxiing to the departure runway of the non-towered airport. According to the mechanic who watched the takeoff, the airplane lifted […]

Condition-based maintenance meets big data and artificial intelligence For the past 20 years, I’ve been preaching the gospel of Reliability-Centered Maintenance (RCM), the then-revolutionary philosophy of maintenance developed in the 1960s at United Airlines by aeronautical engineer Stanley Nowlan and mathermatician Howard Heap. RCM was almost universally adopted by the airlines in the 1970s, by military aviation in the 1980s, and by high-end business aviation in the 1990s. The only segment of aviation that hasn’t yet enthusiastically adopted RCM is owner-flown GA. I’ve made it my personal crusade to change this, and to help drag lightplane maintenance kicking and screaming into the 21st century. RCM arose from a rigorous analysis of historical data by Nowlan & Heap showing that the airlines’ maintenance programs called for more preventive maintenance than necessary, and that such excessive maintenance was actually making aircraft safety and dispatch reliability worse rather than better by increasing the incidence of maintenance-induced failures (MIFs). At the time, these findings were considered heresy by most folks in the airline maintenance organizations, who had been taught to believe that maintenance is a good thing and more maintenance is always better. In spite of these objections, the airlines adopted RCM anyway. Not […]

Is it legal to install uncertified equipment in a certificated aircraft? I receive and answer hundreds of emails each week from aircraft owners, pilots and mechanics who have maintenance-related questions. One I received several weeks ago seems worth sharing: Mike, I need your help. I am a member of flying club, and during the recent annual of our club Skyhawk someone got the bright idea to install automotive seat heaters in the plane without an STC or Form 337. This seems like it might be a violation of the regulations. Is it? Why would our club’s A&P participate in the installation of uncertified equipment and then sign off the aircraft as airworthy? Should I question all the other work this A&P performed? Should I report him to the local FSDO? This pilot’s strong reaction was clearly predicated on his understanding that all equipment in a certificated aircraft must be FAA-approved. Lots of aircraft owners and mechanics believe the same thing. I’ve even heard FSDO inspectors say this. But this common misconception is simply wrong. Let’s examine why. A bit of Googling revealed that there are two kinds of aftermarket automotive seat heaters available: external heating pads that attach to the […]

Why it’s nearly impossible to install a cylinder properly when the engine is on the airplane. Cylinder replacement is a highly invasive and risky procedure with a long history of causing catastrophic in-flight engine failures that cause airplanes to fall out of the sky. I have been personally involved with at least a half-dozen of these maintenance-induced catastrophic engine failures—either as expert witness or investigator—where the engine either “threw a rod” through the crankcase or suffered the complete separation of a cylinder from the engine, resulting in a total loss of power. In some cases, the pilot made a successful forced landing; in others, the outcome was serious injury or death. Cylinder replacement—and especially replacement of multiple cylinders at once—is a procedure that needs to be executed perfectly. If it isn’t, there can be dire consequences. Yet it’s a procedure that most career general aviation A&Ps perform routinely without any apparent concern. Why aren’t these mechanics nervous? Undoubtedly because they are convinced that they always perform the cylinder transplant procedure properly, and that only careless or incompetent mechanics screw it up. That’s wrong, and here’s why. Is “properly” impossible? Roger D. Fuchs—veteran A&P/IA, aircraft engine overhauler, accident investigator, expert witness, […]

When using fasteners loaded in shear, things can get interesting. Last month, I wrote about joints involving threaded fasteners loaded in tension—that is, along the bolt’s longitudinal axis. Such “tension joints” are used to fasten connecting rods to crankshafts, cylinders to crankcases, and even occasionally wings to fuselages (notably in Beechcraft airplanes). I emphasized the critical importance of fastener preload to the structural integrity of such joints and discussed why the most common method of tightening such fasteners (using a torque wrench) is not a particularly good way to establish the correct preload.  But, there’s an entirely different kind of bolted joint: one where the fastener is loaded at right angles to the fastener’s axis. If the plane you fly isn’t a Beechcraft, chances are your wings and tail surfaces are attached to the fuselage by such “shear joints.” In fact, if you fly an aluminum spam can (like I do), it probably has thousands of shear joints—rivets are virtually always loaded in shear, not in tension. However, chances are that the shear joints that fasten your wings and tail feathers use bolts, not rivets, to facilitate them being de-mated from the fuselage. Shear Strength The strength of most shear […]

When using threaded fasteners in tension, it’s all about the preload. Threaded fasteners are ubiquitous in aviation. Look at any GA aircraft and you’ll find hundreds of them if not thousands. They attach wings to the fuselage, cylinders to the crankcase, connecting rods to the crankshaft, and instruments and avionics to the panel. They hold on cowlings, fairings, inspection plates, floorboards, and just about anything else that might need to be removed to gain maintenance access. They’re so numerous and so familiar that we tend to take them for granted. But, when used in safety-critical high-stress applications—like holding on wings, cylinders and connecting rods—there’s complexity to threaded fasteners that is often not well understood or fully appreciated by the maintenance personnel who are responsible for ensuring that they’re safe and secure. Mechanics often don’t treat these critical fasteners with the respect they deserve. The result can be scary. Threaded fasteners go by a variety of names. As a general rule, they are called “bolts” if they are designed to mate with one or two threaded nuts, “screws” if they are designed to mate with a threaded hole in one of the items to be joined, and “studs” if they are […]