AOPA Pilot Magazine

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 […]

Don’t fall victim to an overzealous mechanic. Mark is the owner of a beautiful Cessna 185 Skywagon based in the San Francisco Bay area. Awhile back, Mark and his wife travelled to Minden, Nevada in this airplane to visit with Mark’s mother-in-law who was ill. A few days later, they returned to the airport intending to fly home. But when Mark started the Skywagon’s engine—a Continental IO-520—he saw just about the last thing a pilot wants to see: The oil pressure gauge never budged from the zero mark. [Expletive deleted.] After a brief period of “this can’t be happening!”, mark shut down the engine and started thinking about what to do next. It was a Sunday, of course. (These things always happen on weekends when all the maintenance shops on the field are closed.) The only sign of life at this non-towered airport was the presence of a couple of linemen at the airport’s sole FBO.  Mark approached one of the linemen and asked if he knew of any A&P mechanics in the area that might be able to help with his predicament. The lineman rummaged around in the office and emerged with the phone number of a local A&P […]

Thoughts about being temporarily booted out of my hangar. From the time I first acquired my Cessna 310 in 1987, it has been hangered at Santa Maria Public Airport. Initially, I kept it in a large community hangar. Then in 2003, after a long wait on the airport hangar list, I was able to secure a hangar of my own rom the airport. My hangar is 40 feet wide and 30 feet deep. It easily accommodates my Cessna 310 with lots of room to spare. There’s space for my workbench, my toolbox, a large couch, refrigerator, microwave, and two large shelving units where I keep spare parts, hardware, chemicals and such. It’s not quite as comfortable as some of my neighbor’s hangars—no carpeting, Wi-Fi, or large-screen TV—but it has been a great place to store and work on my airplane over the past 16 years. At first my rent for this nice big hangar was $461 per month. Over the 16 years I’ve occupied it, the rent has gradually increased to its present $692 per month. Still, as hangar rents go, I consider it to be a great deal. If I was based near Los Angeles or San Francisco or […]

What may you do to your aircraft without A&P involvement? More than you might think. The FAA defines who may perform maintenance on certificated aircraft in FAR 43.3. This rule lists all the usual certificated suspects: mechanics, repair stations, air carriers, repairmen employed by a repair station or air carrier, and (under certain conditions) aircraft, engine, propeller and appliance manufacturers. The rule also permits maintenance to be done by ordinary non-certificated folks provided it’s done under the supervision of and approved by a certificated mechanic. Beyond that, FAR 43.3 permits a pilot to perform preventive maintenance on an aircraft owned or operated by that pilot, provided the aircraft is used strictly for non-commercial operations under Part 91. Pilots may do this all by themselves without any A&P involvement.  How cool is that? What exactly is this preventive maintenance stuff that pilots are permitted to do on their own recognizance? Ah, there lies the rub! The phrase “preventive maintenance” is defined in FAR 1.1 (Definitions) as follows: “Preventive maintenance means simple or minor preservation operations and the replacement of small standard parts not involving complex assembly operations.”  That’s about as clear as mud. What exactly are preservation operations? Which ones are […]

The Friendlies are remarkably friendly to Part 91 folks Aircraft owners and pilots love to bash the FAA. We grumble and whine about all the labyrinthine regulations and requirements the Agency burdens us with, and how much it increases our complexity and cost of flying. I’m occasionally guilty of this myself—witness my “Double Standard?” column in last month’s AOPA PILOT in which I kvetched about the FAA’s failure to require A&Ps to undergo recurrent training and re-evaluation. In truth, we Part 91 operators have it pretty darn good compared with our brethren in almost every other nation on the planet. We also have it exceptionally good compared with charter operators (Part 135) or air carriers (Part 121) or large aircraft in non-commercial operations (Part 125). This isn’t by accident. It’s in accordance with one of the FAA’s most fundamental guiding principles—something the Agency polysyllabically calls the “Safety Continuum.”   “Safety Continuum: The level of safety established by regulation, guidance and oversight that change based on risk and societal expectations of safety. The safety continuum applies an appropriate level of safety from small UAS to large transport category aircraft. The differing level of safety balances the needs of the flying public, applicants and […]

Why aren’t A&Ps trained as well as pilots are? I never really wanted to become an A&P. All I really wanted was to be able to maintain my own airplane without adult supervision.  Heck, I’d been doing virtually all the maintenance of my 1979 Cessna Turbo 310 myself for about 10 years. The various A&Ps who had agreed to supervise me all agreed that I now knew more about the maintenance aspects of my than any of them did. It seemed like high time for me to take full responsibility for my work and be able to sign it off. All I really wanted was something like the Limited Repairman Certificate that the FAA grants to the builder of an Experimental Amateur-Built (E-AB) aircraft that permits them to maintain their own machine. I had absolutely no desire to swing wrenches on any aircraft other than my own. Sadly, the FAA offers nothing comparable for the owner of a certificated aircraft who wants to do his own maintenance (although I certainly wish they did).  My only option was to earn an A&P mechanic certificate. It was an all-or-nothing proposition. The FAA sure doesn’t make it easy to earn an A&P certificate. […]

When things go awry in the sky, litigation isn’t necessarily the best remedy. My email inbox contained a message with the subject “Legal Question – Advice Needed.” That didn’t surprise me because although I’m not a lawyer, I do regularly participate in aviation litigation—mostly arising from air crashes—as an expert witness and consultant, mainly in cases that involve mechanical or maintenance issues. The email was from a private pilot who owned a Liberty XL2 that he purchased used nine months earlier. After he flew the aircraft for about 80 hours, the aircraft’s Continental IOF-240-B engine developed a serious engine problem that revealed itself by a low oil pressure indication. The owner’s mechanic ultimately traced the problem to the cluster gear on the rear of the engine’s crankshaft, which was found to be damaged where the starter pinion engaged the cluster gear at each engine start. “The metal from the damaged gear contaminated the engine and ultimately caused catastrophic damage to the engine,” the owner explained. “I was very lucky that I was not in flight as I was holding short and just seconds from takeoff clearance when I noticed the low oil pressure alarm. The engine still ran and I […]

Understanding aircraft insurance If you own an aircraft, you probably have aircraft insurance. Whether it’s the right amount of the right coverages is worth exploring. Here’s what I’ve learned in my 50+ years of aircraft ownership plus extensive discussions with veteran industry insiders who have forgotten more than I’ll ever know on the subject. Anatomy of a policy All insurance policies are contracts in which the insurer promises to pay benefits to the insured if certain defined events occur, provided that the insured has paid the agreed-to premium and met certain other conditions. Policies are contracts of adhesion, meaning that the insurer drafts the contract and offers it on pretty much a take-it-or-leave-it basis. This can pose a trap: Insureds rarely receive a copy of the policy until after they’ve already agreed to it, and even then they rarely read it. The good news is that courts tend to interpret any policy ambiguities in favor of the insured. Insurance policies can appear intimidating, but they’re not that complicated. They consist of two sections: a declaration (which identifies the insured, the insurer, the policy period, the premium amount, the kinds and maximum limits of coverage, and any applicable deductibles), and the […]

Before doing something expensive or invasive, slow down “My Cirrus SR22’s oil pressure has been slowly decreasing,” reported Oliver, one of my company’s managed maintenance clients. “At full power the pressure used to be 41-43 PSI, but over the past three months it has dropped to 36-39, and half the time I get a low oil pressure warning at idle. Should I get this checked now, or wait until the annual?” Oliver’s account manager Eric—a very experienced A&P/IA and one of the savviest engine guys in our company—advised that this should be checked sooner rather than later. “Oil pressure in the 30s is too low,” Eric told Oliver. “I would actually prefer to see it around 50 PSI. It’s easy to adjust oil pressure. Let’s have that done no later than the next oil change.” Oliver normally has his airplane maintained at the small shop on his home field, but the shop was booked solid and told Oliver that they couldn’t put his plane on the shop schedule for at least three or four weeks. Oliver checked with several other small shops, who all told him the same story. Now quite concerned about his decreasing oil pressure and wanting to […]

Not preheating a cold engine is a effective way to damage it Preheating is important. A single cold start without proper preheating can produce more wear on your engine in less than a minute than 500 hours of normal cruise operation  I’m often asked how cold it has to be before preheating is necessary. There’s no hard and fast answer, because the damage done by an unpreheated cold start depends on a variety of things, including the type of engine, its age and condition, and what kind of oil is being used. A brand new or freshly rebuilt or overhauled engine is more vulnerable to cold start damage than a tired old engine at TBO. Generally, I consider any start in which the engine is cold-soaked to a temperature below freezing (32°F or 0°C) to be a misdemeanor and any start below about 20°F (–7°C) to be a felony. The colder the temperature, the worse the crime (and the ensuing punishment). A common misconception is that the main reason cold starts are bad for engines is that the engine oil is thick and viscous and doesn’t flow well. Since it takes longer for oil pressure to come up when the […]

Reviving an engine that has been inactive for months or years Piston aircraft engines hate to sit unflown. During lengthy periods of disuse, the protective oil film strips off critical surfaces like cylinder walls, cam lobes and tappet faces, exposing them to risk of corrosion pitting. Then afterwards, when the engine is finally “dry started” with the oil film depleted, these critical surfaces can be subject to abnormal friction and wear until oil flow is restored and these splash-lubricated surfaces get coated with oil once again. The engine suffers as a result. Unfortunately, this sort of thing happens a lot. My own Cessna 310 was grounded on November 1st when its annual expired. My planning was to complete the annual in December, but I wound up catching a nasty virus that had me confined to quarters for a couple of weeks. Now it’s looking like the plane won’t be ready to fly again until late January. My engines are not happy about this. Recently I was contacted by a pilot who acquired a 1968 Shrike Commander that had been sitting unflown in a hangar in Oregon for the past 14 years. The new owner asked me for suggestions on how […]

When mechanics get interrupted, bad things can happen I was recently contacted by the owner of a Cessna Hawk XP (R172K)—I’ll call him “Sam”—who seemed rather shaken by a recent series of events. He told me he was a student pilot with solo flight privileges and ready to make his first solo cross-country flight in pursuit of a private pilot certificate. Sam and his CFI had flown the Hawk from its home base to a small well-regarded maintenance shop at a nearby airport for some adjustments to the fuel system of the airplane’s Continental IO-360 engine. At the shop, the A&P/IA—I’ll call him “Rick”—found leaks in the system and recommended that the fuel system be removed sent out for overhaul. Sam agreed to this, and since this would ground the plane for several weeks and its annual inspection was coming due not long afterwards, Sam asked Rick to perform an annual inspection on the airplane while the fuel system was being overhauled. About six weeks later, Rick called Sam to advise that the aircraft was ready for pickup. Sam and his CFI went to the shop to fly the plane back to its home base. They pre-flighted the aircraft and […]

Taking the complexity out of cylinder break-in From time to time, every piston aircraft owner faces the question of how best to break-in new cylinders. Sometimes this involves just one or two newly-replaced cylinders, other times all cylinders have been replaced simultaneously (“top overhaul”), and yet other times the entire engine has been major overhauled or exchanged for a new or rebuilt. Regardless, the cylinders must be properly broken in. It’s not hard to do this, but it’s also not hard to screw it up and that can be a costly and frustrating mistake. If you Google the phrase “aircraft cylinder break-in” you’ll be amazed at how much has been written on this subject. Each engine manufacturer has a service bulletin to provide guidance on how to do this (e.g., Continental M89-7R1, Lycoming SI 1427B), as do manufacturers of PMA cylinders (e.g., ECi, Superior). Many well-known engine overhaul shops provide their own break-in instructions (e.g., RAM, Penn Yan, Victor), and various type clubs have also weighed in on the subject. Even Shell Oil has written its own break-in recommendations.  If you digest this myriad guidance, you’ll probably find yourself seriously confused. Although there are some common threads that everyone seems […]