Archive for the ‘Aircraft ownership and maintenance’ Category

Life on the Trailing Edge

Tuesday, August 26th, 2014

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

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

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

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

Tire Tactics

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

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

Goodyear vs. Desser retreads

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

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

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

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

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

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

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

Spark Plug Wars

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

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

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

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

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

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

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

Where’s the Beef?

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

Tortoise and hare

Why are so many A&Ps late-adopters?

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

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

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

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

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

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

Regulations Are Written In Blood: Why Planesharing Is Grounded For Now

Thursday, August 7th, 2014

 

planesharing is grounded until further notice

In aviation, we say that “regulations are written in blood.” Pilots often complain about regulations, but they generally recognize that those regulations are often based on experience and events that have cost others their property, their lives, or both. We know that the legal environment of aviation often lags behind reality. Technical innovations can make older regulations obsolete. But sometimes the innovation doesn’t change the relevance of the regulations or dilute the blood in which they are written.

Planesharing Explained

Laws should serve as a safety net, not a noose. Aircraft are expensive to own and operate. Now, more than ever, making aircraft more useful and ubiquitous is critical for the survival of aviation. Uber, Lyft, AirBnB, VBRO, GetAround, and BoatBound make it easy to put substantial assets like cars, boats, and homes to work. There is no federal statute that makes renting out your spare bedroom generally illegal.

“Planesharing” tries to apply the same model to private air travel. Planesharing is the concept of pilots use services on the Internet to post details of their upcoming flights in the hopes that potential passengers will find the flight information, join the pilots on their flights, and split the cost of the flight with them.

Startups like Flytenow, AirPooler, ShareMySky, AiirShare, Pro Rata Share, Wingman, and others have developed business models around facilitating planesharing. Venture capital should not be seen as some kind of signal that startups can ignore the rules the rest of us have to live by.

Pilots have been legally sharing the costs of privately operated flights for decades, but purpose-built online apps like these have made this kind of sharing more like commercial flying.

How Private and Commercial Flying are Different

It is sometimes said that the most dangerous part of a flight is the drive to the airport. That’s true, but only if you’re flying with a commercial operation. Airline (Part 121) and charter (Part 135) flying is something like 500 times safer than operations conducted by private pilots (generally conducted under Part 91). There’s good reason for this. Airlines and charter operators have to achieve rigorous certification of their aircraft, facilities, operations, and pilots and maintain that certification through constant monitoring, training, and investment. If you look at the Federal Aviation Regulations (FARs) in printed form, the requirements take up about an inch of thickness and that’s just the regulations themselves. Aircraft inspections happen at least every 100 hours of operating time. Operating specifications, maintenance records, pilot manuals, maintenance manuals, dispatcher manuals, and other necessary paperwork fills many linear feet of shelf space. Pilot experience could be as low as 250 or so hours, but most pilots flying for commercial operations have thousands.

Private operations, (under Part 91) on the other hand, don’t have to do as much. They’re subject to maybe a half inch of regulations and a few operating manuals. Private pilots might have as little as 50 hours of flight time. A mechanic may only be required to even touch the aircraft once a year.

It’s reasonable to accept more risk when flying with a private individual vs. a commercial operator. Flying a helicopter in combat has a lower accident rate than flying single piston engine airplanes. Remember folks, flying isn’t necessarily dangerous, but it is terribly unforgiving.

The Regulations and How Planesharing Gets Pilots In Trouble

This difference is the basis for the different FAA regulations for commercial and private operations. The regulation that applies to private pilots (FAR 61.133) says that “no person who holds a private pilot certificate may act as pilot in command of an aircraft that is carrying passengers or property for compensation or hire; nor may that person, for compensation or hire, act as pilot in command of an aircraft.” That same regulation goes on to say that “a private pilot may not pay less than the pro rata share of the operating expenses of a flight with passengers, provided the expenses involve only fuel, oil, airport expenditures, or rental fees.”

Planesharing depends on the “pro rata share” part of the regulation. As long as a private pilot operating under Part 91 collects only part of the money for the flight, he or she is in the clear, right? But let’s be honest. Privately this easy, and only when you start fishing about for people we have no prior relationship with do any of these new apps make anything easier. Blurring the lines between private and commercial flying is a problem. The confusion is in the uninitiated passenger believing that he or she is getting the commercial level of safety when the pilot is operating under the much more permissive rules of Part 91.

So the FAA typically applies a two-part litmus test.

1. Is the pilot “holding out” the service to the public? Put another way: How much does an operation look like an airline or charter service? FAA Advisory Circular AC-120-42 says that one becomes “a common carrier [i.e., an operation that requires the more rigorous certification] when it holds itself out or to a segment of the public as willing to furnish transportation within the limits of its facilities to any person who wants it.” What does a planesharing pilot do? Lists his or her flight and invites anyone with money to come sit in one of the other seats, right? Short of the person being overweight for the aircraft or being disagreeable in some way, a planesharing pilot is offering to furnish transportation to all comers.

2. Do the pilot and the passenger(s) have “common purpose” for the flight? The regulations (and all FAA guidance and rulings to date) clearly contemplate friends or family loading into a Cessna 172 and flying somewhere for dinner or sightseeing. The FAA requires that everyone in the aircraft have something in common about the mission. Planesharing encourages passengers who have no preexisting relationship with the pilot (otherwise, why is an online service necessary for them to find each other?) and it is almost certain that the pilot and passengers will have different objectives once they arrive at the destination. What are the chances that perfect strangers will turn out to be heading to the same golf course, restaurant, or shopping district? Even local flights which start and end at the same airport, which the FAA regulates as sightseeing flights are regulated. Air tour pilots are required to keep within a limited distance from the airport, submit to more drug tests, and hold at least a commercial pilot certificate.

It is possible to engage in planesharing in a compliant way. You build a group of friends over time, say on Pilots of America or a similar message board. You all agree to meet at a regional airport and fly in Bob’s Cessna 206 down to Sun ‘N Fun in Florida in March for three days to see the airshow and drool on the latest aircraft. You split the cost when it’s all over. Great.

But, if we’re being honest with ourselves, does anyone really think that many planesharing flights would work this way? A majority of them? Fewer? Any? The FAA administrator and staff are reasonably intelligent. The FAA can identify a sham when the FAA sees a sham and so can we. We need to be honest with ourselves and admit that most flights under the planesharing model are not legal under the current regulations. The arguments made by these companies that the rules don’t apply to them just don’t hold water.

Could the FAA come up with a safe harbor under the rule? Sure. What would that look like? A demonstrable pre-existing relationship between the pilot and passengers of at least such-and-such a duration, supported by family relationship or documentary evidence like date-stamped e-mail correspondence? A requirement that pilot and passengers all do the same thing at the destination, supported by a file folder full of consecutively-numbered concert tickets or a guest check with the appropriate number of entrees?

At what point do the administrative costs outweigh the benefit of such a safe harbor? It’s complicated. Previous legal interpretations from the FAA like here and here make this clear as mud. Creating a safe harbor under current regulation would be really tough. We’ve got to balance personal choice with public expectations of safety.

Anyway, we’re going to find out soon.  At least AirPooler and FlyteNow have petitioned the FAA for an administrative ruling about the legality of planesharing. The FAA told the pilot community that it would rule by mid-June, but that deadline has come and gone while the FAA continues to think about the issue. In the meantime, good on AirPooler for recently advising pilots to hold off on listing flights pending the FAA’s ruling. My opinion doesn’t really count for much. The ball is in the FAA’s court. Enforcement actions are possible and even likely before the smoke clears.

Why So Serious?

If you’ve read this far, you might wonder why I’m disparaging a potentially helpful and cool new aspect of the sharing economy. I love innovation and new ideas as much as anyone. I have a dog in this fight. But it’s a different dog and I’ve defined the fight for what I believe is a better way.

For aviation, collaborative consumption isn’t anything new. We’ve been buying and leasing back airplanes to flight schools and flying clubs for decades. The rest of the world was just catching up with us. There’s still plenty of room for innovation in the business of aviation. Two of my favorite examples are ForeFlight and SurfAir. They’ve disrupted the experience, without ignoring the rules.

Regulation and innovation can coexist. My own example is OpenAirplane which tackles the problem that we can solve legally by making more aircraft accessible to more pilots. The idea is to make everyone’s pilot certificate more useful.

In a nutshell: It used to be that each airplane rental operation (and its insurance company) required that a pilot do a local checkout flight in the airplane before renting it. OpenAirplane standardized the checkout process and with support of insurance industry. Now, pilots go through a single annual checkout flight that tests their skills and verifies that they are as safe and competent as the FAA requires. The standards are pretty much the same ones that the FAA uses when initially certifying pilots and they’re evaluated by designated flight instructors who are familiar with the process. After that Universal Pilot Checkout, the pilot can rent the same kind(s) or airplane(s) at any participating facility (currently more than 60 across the US). It’s all completely legal.

While planesharing could expand the addressable market for our company, we’re not willing to put pilots at risk of violations or worse. OpenAirplane solves as much of the problem as we can solve without breaking the law. We put more pilots in more airplanes more often. We don’t do anything for non-pilot passengers yet, but only because – well – illegal.

But we still frequently get lumped in with planesharing operators when folks talk about developments in aircraft availability. We’re not a planesharing operation. And we don’t want to be unless he rules change. Planesharing can’t solve the problem that it claims to solve without a deregulation of private aviation or a big shift in FAA doctrine.

You Can’t Fool Newton and Bernoulli

The principles defined by Isaac Newton and Daniel Bernoulli govern the safety of flight. They don’t care about social networks or online collaboration, no matter how innovative or cute. And mountains of evidence tell us that Newton and Bernoulli favor the better-maintained aircraft, better-trained pilots, and more comprehensive operating procedures that one finds almost exclusively in commercial operations. As long as the safety of passengers – or at least honesty with passengers about the wildly different risk profile that they face in an aircraft with the average a planesharing pilot – is the point, planesharing doesn’t work.

The FAA regulations allocate privileges to pilots based on a careful balancing of those privileges with the skills and experience that they have demonstrated. Planesharing, as currently conceived and practiced, encourages private pilots to operate de facto charter services or air carriers. It’s a bad idea. Unless the FAA reverses its position, planesharing remains grounded.

Money Well-Spent

Tuesday, July 22nd, 2014

I won’t lie to you, owning an airplane will lighten your wallet. As the owner of multiple types of light airplanes over multiple years I consider myself an expert on flying budgets. To minimize the pain and angst involved in budgeting I separate my expenses into known and unknown, fixed and variable, and I do my rough budgeting by calculating an equation on an annual basis, with quarterly check ups. That way I don’t fret over expenses on every flight, because, frankly, fretting takes the fun out of flying. 

My fixed budget items for my light single engine aircraft include insurance and maintenance, oil and storage. These are items I can easily get an annual bead on. I add them up and call them “F”. Variables include fuel and miscellaneous trip costs, plus unexpected maintenance; but even these I can rough out a year in advance based on prior knowledge (I’ve been at this for two and a half decades, which helps). These each get their own designation in the equation, since they can change independently.

It helps that my operating hours are pretty consistent every year. I know I’ll probably put 150 hours on the traveling machine, and 50 hours on the “kick-around-the-patch” bird. That gives me another constant in my equation.

Yes, fuel is a sticky variable. It goes up, it goes down. Even my best estimate can fly out the window when world politics play havoc with supply and demand (or the perception of supply, in many cases). That’s why I tend to go fat on my estimate. This year, for instance, I ball-parked my fuel costs at $6 per gallon, even though the fuel at my home base runs more than a dollar a gallon less. By overestimating by about 15% I give myself a little room.

Same goes for maintenance. If I ball park using a 15% markup on my mechanic’s hourly rate to pad for unknown costs on the road I’m in better shape. Parts, well, that can get interesting. Best to throw, say $3,000 in the pot and if I don’t use it, well, that’s $3,000 more in the reserve for the “next engine pile” next year.

FBO costs are next. I know some FBOs waive parking fees with a fuel purchase, but rarely for every night of your stay. And there are times, particularly when weather threatens, that you want your airplane in a hangar. That’s gonna cost you. By building those costs into my flying budget ahead of time I take the stress out of saying “yes” when I’m offered the protection of a hangar on a stormy night in the hinterlands.

Frankly, the entire exercise each spring is about eliminating my money-stress around flying. That way I can simply enjoy the privilege of being airborne in my own private craft, as PIC. It’s a privilege I worked long and hard to afford, then to qualify for, and, finally, it is a privilege I cherish and advocate for. The last thing I want to do is let the anxious smell of money to get in the way of the very activity that brings me peace and serenity.

Want to take the sting out of your operations? Here’s my formula:

Flying cost = (Time aloft x Fuel used)+ (FBO cost x Trip legs) + (Parts + maintenance cost) + Fixed costs (insurance, oil, storage)

Don’t forget to keep that pile of money growing for your next engine, too. Happy contrails!

What Makes an Engine Airworthy?

Wednesday, July 2nd, 2014

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

Bob Moseley

James Robert “Bob” Moseley (1948-2011)

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

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

Which Engine Is Airworthy?

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

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

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

Who has the most airworthy engine? And why?

Compression/Oil Level

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

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

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

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

Lesson of a Lawn Mower

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

Snapper Lawnmower

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

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

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

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

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

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

Common Sense 101Let’s Use Common Sense

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

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

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

On-Condition Maintenance

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

Digital borescope (Adrian Eichhorn)

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

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

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

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

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

When Is It Time to Overhaul?

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

Lycoming cam and lifter

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

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

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

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

Prepping the long X-C

Monday, June 23rd, 2014

It is now one month before my annual summer airborne trek and, yes, preparation has already begun. In fact, my task list for these long summer outings starts a few months ahead, if you want to include the time I spend reserving hotel or condo space and cars in the most popular places (I use AOPA’s web discounts to help make it all affordable). That’s just good planning.

I double check all the paperwork for the year is good with my airplane. It generally goes through its condition check—the equivalent of an annual inspection—in April, and by late May any sore points have have been completely worked out by my A&P. In June it is time to ensure that all of my GPS and MFD databases will stay up to date throughout my journey.

It’s also when I start a push on my own pilot currency, to make sure that I’m ready for any of the weather my long cross country is liable to toss at me.  I never want to feel as if my skills aren’t up to the conditions. I hit the PC sim in my office to practice my procedures. Then I rustle up my flight instructor and torture him with a couple sessions of practice approaches, navigation, holding patterns and emergencies.

The emergencies are something I always have in the back of my mind. By the end of June, once I know

Emergency kits come in all shapes and sizes. Alternatively, you can build your own.

my general routing for the summer trip, I start gathering fresh supplies for my emergency back pack, which sits just behind the pilot’s seat (not in the baggage compartment where I can’t reach it without getting out of my seat). The back pack holds packaged water, a mylar blanket and first aid supplies for dealing with cuts, scrapes and “bleeders.” It also has a strobe light, signal mirror, emergency cryovac food and a multipurpose tool. We’ve got a tiny two-person tent that barely weighs five pounds packed, and if we’re going over a lot of wide-open space that’s worth tucking in next to my husband’s emergency tool kit, too.

That tool kit has come in handy more times than not. These adventures put more hours on our airplane than it often flies in the three months after we return. And hours mean wear and tear. We have, on occasion, even been seen to carry a spare part or two in our cargo area. Overcautious? Depends on where you are going. Do you know how much it costs to replace an alternator on Grand Cayman, or Roatan?

Once I’ve got my emergency back pack, tool kit and any spare parts together I can begin thinking about

AOPA's airport information web application can help you pick a fuel stop.

AOPA’s airport information web application can help you pick a fuel stop.

the routing. I know how far my airplane can safely go in one leg, and I know how long I can safely go, say, before I have to “go.” In early July I begin checking flight planning software and comparing possible fuel stops. Because I don’t know what the weather will be on my day of departure, and because fuel prices fluctuate, I always have two or three potential airports planned for each fuel stop. I’ll narrow it down the night before I leave, and even still, I might not make a final choice until I’m airborne and I see what the real flight conditions are like.

It sounds like a lot of work, getting ready for an epic trip. It can be, if you look at it as work. I see all the prep as part of the build-up, the anticipation that is half the fun of going. With that attitude, starting flight preparations early is all part of the fun.

The Dark Side of Maintenance

Tuesday, June 10th, 2014

The Dark SideHave you ever put your airplane in the shop—perhaps for an annual inspection, a squawk, or a routine oil change—only to find when you fly it for the first time after maintenance that something that was working fine no longer does?  Every aircraft owner has had this happen. I sure have.

Maintenance has a dark side that isn’t usually discussed in polite company: It sometimes breaks aircraft instead of fixing them.

When something in an aircraft fails because of something a mechanic did—or failed to do—we refer to it as a “maintenance-induced failure”…or “MIF” for short. Such MIFs occur a lot more often than anyone cares to admit.

Why do high-time engines fail?

I started thinking seriously about MIFs in 2007 while corresponding with Nathan Ulrich Ph.D. about his ground-breaking research into the causes of catastrophic piston aircraft engine failures (based on five years’ worth of NTSB accident data) that I discussed in an earlier post. Dr. Ulrich’s analysis showed conclusively that by far the highest risk of catastrophic engine failure occurs when the engine is young—during the first two years and 200 hours after it is built, rebuilt or overhauled—due to “infant-mortality failures.”

But the NTSB data was of little statistical value in analyzing the failure risk of high-time engines beyond TBO, simply because so few engines are operated past TBO; most are arbitrarily euthanized at TBO. We don’t have good data on how many engines are flying past TBO, but it’s a relatively small number. So it’s s no surprise that the NTSB database contains very few accidents attributed to failures of over-TBO engines. Because there are so few, Ulrich and I decided to study all such NTSB reports for 2001 through 2005 to see if we could detect some pattern of what made these high-time engines fail. Sure enough, we did detect a pattern.

About half the reported failures of past-TBO engines stated that the reason for the engine failure could not be determined by investigators. Of the half where the cause could be determined, we found that about 80% were MIFs. In other words, those engines failed not because they were past TBO, but because mechanics worked on the engines and screwed something up!

Sheared Camshaft Bevel GearCase in point: I received a call from an aircraft owner whose Bonanza was undergoing annual inspection. The shop convinced the owner to have his propeller and prop governor sent out for 6-year overhauls. (Had the owner asked my advice, I’d have urged him not to do this, but that’s another story for another blog post.)

The overhauled prop and governor came back from the prop shop and were reinstalled. The mechanic had trouble getting the prop to cycle properly, and he wound up removing and reinstalling the governor three times. During the third engine runup, the the prop still wouldn’t cycle properly. The mechanic decided to take the airplane up on a test flight anyway (!) which resulted in an engine overspeed. The mechanic then removed the prop governor yet again and discovered that the governor drive wasn’t turning when the crankshaft was rotated.

I told the owner that I’d seen this before, and the cause was always the same: improper installation of the prop governor. If the splined drive and gears aren’t meshed properly before the governor is torqued, the camshaft gear is damaged, and the only fix is a teardown. (A couple of engine shops and a Continental tech rep all told the owner the same thing.)

This could turn out to be a $20,000 MIF. Ouch!

How often do MIFs happen?

They happen a lot. Hardly a day goes by that I don’t receive an email or a phone call from an exasperated owner complaining about some aircraft problem that is obviously a MIF.

A Cessna 182 owner emailed me that several months earlier, he’d put the plane in the shop for an oil change and installation of an STC’d exhaust fairing. A couple of months later, he decided to have a digital engine monitor installed. The new engine monitor revealed that the right bank of cylinders (#1, #3 and #5) all had very high CHTs well above 400°F. This had not shown up on the factory CHT gauge because its probe was installed on cylinder #2. (Every piston aircraft should have an engine monitor IMHO.) At the next annual inspection at a different shop, the IA discovered found some induction airbox seals missing, apparently left off when the exhaust fairing was installed. The seals were installed and CHTs returned to normal.

Sadly, the problem wasn’t caught early enough to prevent serious heat-related damage to the right-bank cylinders. All three jugs had compressions down in the 30s with leakage past the rings, and visible damage to the cylinder bores was visible under the borescope. The owner was faced with replacing three cylinders, around $6,000.

Sandel SN3308The next day, I heard from the owner of an older Cirrus SR22 complaining about intermittent heading errors on his Sandel SN3308 electronic HSI. These problems started occurring intermittently about three years earlier when the shop pull the instrument for a scheduled 200-hour lamp replacement.

Coincidence?

I’ve seen this in my own Sandel-equipped Cessna 310, and it’s invariably due to inadequate engagement between the connectors on the back of the instrument and the mating connectors in the mounting tray. You must slide the instrument into the tray just as far as possible before tightening the clamp; otherwise, you’ve set the stage for flaky electrical problems. This poor Cirrus owner had been suffering the consequences for three years. It took five minutes to re-rack the instrument and cure the problem.

Pitot-Static PlumbingNot long after that, I got a panicked phone call from one of my managed-maintenance clients who’d departed into actual IMC in his Cessna 340 with his family on board on the first flight after some minor avionics work. (Not smart IMHO.) As he entered the clag and climbed through 3,000 feet, all three of his static instruments—airspeed, altimeter, VSI—quit cold. Switching to alternate static didn’t cure the problem. The pilot kept his cool, confessed his predicament to ATC, successfully shot an ILS back to his home airport, then called me.

The moment I heard the symptoms, I knew exactly what happened because I’d seen it before. “Take the airplane back to the avionics shop,” I told the owner,  “and ask the tech to reconnect the static line that he disconnected.” A disconnected static line in a pressurized aircraft causes the static instruments to be referenced to cabin pressure. The moment the cabin pressurizes, those instruments stop working. MIF!

I know of at least three other similar incidents in pressurized singles and twins, all caused by failure of a mechanic to reconnect a disconnected static line. One resulted in a fatal accident, the others in underwear changes. The FARs require a static system leak test any time the static system is opened up, but clearly some technicians are not taking this seriously.

Causes of Accidents

Why do MIFs happen?

Numerous studies indicate that three-quarters of accidents are the fault of the pilot. The remaining one-quarter are machine-caused, and those are just about evenly divided between ones caused by aircraft design flaws  and ones caused by MIFs. That suggests one-eighth of accidents are maintenance-induced, a significant number.

The lion’s share of MIFs are errors of omission. These include fasteners left uninstalled or untightened, inspection panels left loose, fuel and oil caps left off, things left disconnected (e.g., static lines), and other reassembly tasks left undone.

Distractions play a big part in many of these omissions. A mechanic installs some fasteners finger-tight, then gets a phone call or goes on lunch break and forgets to finish the job by torqueing the fasteners. I have seen some of the best, most experienced mechanics I know fall victim to such seemingly rookie mistakes, and I know of several fatal accidents caused by such omissions.

Maintenance is invasive!

Whenever a mechanic takes something apart and puts it back together, there’s a risk that something won’t go back together quite right. Some procedures are more invasive than others, and invasive maintenance is especially risky.

Invasiveness is something we think about a lot in medicine. The standard treatment for gallstones used to be cholecystectomy (gall bladder removal), major abdominal surgery requiring a 5- to 8-inch incision. Recovery involved a week of hospitalization and several weeks of recovery at home. The risks were significant: My dad very nearly died as the result of complications following this procedure.

Nowadays there’s a far less invasive procedure—laproscopic cholecystectomy—that involves three tiny incisions and performed using a videoscope inserted through one incision and various microsurgery instruments inserted through the others. It is far less invasive than the open procedure. Recovery usually involves only one night in the hospital and a few days at home. The risk of complications is greatly reduced.

Similarly, some aircraft maintenance procedures are far more invasive than others. The more invasive the maintenance, the greater the risk of a MIF. When considering any maintenance task, we should always think carefully about how invasive it is, whether the benefit of performing the procedure is really worth the risk, and whether less invasive alternatives are available.

Ryan Stark of Blackstone LabsFor example, I was contacted by an aircraft owner who said that he’d recently received an oil analysis report showing an alarming increase in iron. The oil filter on his Continental IO-520 showed no visible metal. The lab report suggested flying another 25 hours and then submitting another oil sample for analysis.

The owner showed the oil analysis report to his A&P, who expressed grave concern that the elevated iron might indicate that one or more cam lobes were coming apart. The mechanic suggested pulling one or two cylinders and inspecting the camshaft.

Yikes! What was this mechanic thinking? No airplane has ever fallen out of the sky because of a cam or lifter problem. Many have done so following cylinder removal, the second most invasive thing you can do to an engine. (Only teardown is more invasive.)

The owner wisely decided to seek a second opinion before authorizing this exploratory surgery. I told him the elevated iron was almost certainly NOT due to cam lobe spalling. A disintegrating cam lobe throws off fairly large steel particles or whiskers that are usually visible during oil filter inspection. The fact that the oil filter was clean suggested that the elevated iron was coming from microscopic metal particles less than 25 microns in diameter, too small to be detectable in a filter inspection, but easily detectable via oil analysis. Such tiny particles were probably coming either from light rust on the cylinder walls or from some very slow wear process.

I suggested the owner have a borescope inspection of his cylinders to see whether the bores showed evidence of rust. I also advised that no invasive procedure (like cylinder removal) should ever be undertaken solely on the basis of a single oil analysis report. The oil lab was spot-on in recommending that the aircraft be flown another 25 hours. The A&P wasn’t thinking clearly.

Even if a cam inspection was warranted, there’s a far less invasive method. Instead of a 10-hour cylinder removal, the mechanic could pull the intake and exhaust lifters, and then determine the condition of the cam by inspecting it with a borescope through the lifter boss and, if warranted, probing the cam lobe with a sharp pick. Not only would this procedure require just 15% as much labor, but the risk of a MIF would be nil.

Sometimes, less is more

Many owners believe—and many mechanics preach—that preventive maintenance is inherently a good thing, and the more of it you do the better. I consider this wrongheaded. Mechanics often do far more preventive maintenance than necessary and often do it using unnecessarily invasive procedures, thereby increasing the likelihood that their efforts will actually cause failures rather than preventing them.
Mac Smith RCM Seminar DVDAnother of my earlier posts discussed Reliability-Centered Maintenance (RCM) developed at United Airlines in the late 1960s, and universally adopted by the airlines and the military during the 1970s. One of the major findings of RCM researchers was that preventive maintenance often does more harm than good, and that safety and reliability can often be improved dramatically by reducing the amount of PM and using minimally invasive techniques.

Unfortunately, this thinking doesn’t seem to have trickled down to piston GA, and is considered heresy by many GA mechanics because it contradicts everything they were taught in A&P school. The long-term solution is for GA mechanics to be trained in RCM principles, but that’s not likely to happen any time soon. In the short term, aircraft owners must think carefully before authorizing an A&P to perform invasive maintenance on their aircraft. When in doubt, get a second opinion.

The last line of defense

The most likely time for a mechanical failure to occur is the first flight after maintenance. Since the risk of such MIFs is substantial, it’s imperative that owners conduct a post-maintenance test flight—in VMC , without passengers, preferably close to the airport—before launching into the clag or putting passengers at risk. I think even the most innocuous maintenance task—even a routine oil change—deserves such a post-maintenance test flight. I do this any time I swing a wrench on my airplane.

You should, too.

Quest for a TBO-Free Engine

Tuesday, May 13th, 2014

“It just makes no sense,” Jimmy told me, the frustration evident in his voice. “It’s unfair. How can they do this?”

Jimmy Tubbs, ECi’s legendary VP of Engineering

Jimmy Tubbs, ECi’s legendary VP of Engineering

I was on the phone with my friend Jimmy Tubbs, the legendary Vice President of Engineering for Engine Components Inc. (ECi) in San Antonio, Texas. ECi began its life in the 1940s as a cylinder electroplating firm and grew to dominate that business. Starting in the mid-1970s and accelerating in the late 1990s—largely under Jimmy’s technical stewardship—the company transformed itself into one of the two major manufacturers of new FAA/PMA engine parts for Continental, Lycoming and Pratt & Whitney engines (along with its rival Superior Air Parts).

By the mid-2000s, ECi had FAA approval to manufacture thousands of different PMA-approved engine parts, including virtually every component of four-cylinder Lycoming 320- and 360-series engines (other than the Lycoming data plate). So the company decided to take the next logical step: building complete engines. ECi’s engine program began modestly with the company offering engines in kit form for the Experimental/Amateur-Built (E-AB) market. They opened an engine-build facility where homebuilders could assemble their own ECi “Lycoming-style” engines under expert guidance and supervision. Then in 2013, with more than 1,600 kit-built engines flying, ECi began delivering fully-built engines to the E-AB market under the “Titan Engines” brand name.

Catch 22, FAA-style

ECi’s Titan Exp experimental engine

A Titan engine for experimental airplanes.
What will it take to get the FAA to certify it?

Jimmy is now working on taking ECi’s Titan engine program to the next level by seeking FAA approval for these engines to be used in certificated aircraft. In theory, this ought to be relatively easy (as FAA certification efforts go) because the Titan engines are nearly identical in design to Lycoming 320 and 360 engines, and almost all the ECi-built parts are already PMA approved for use in Lycoming engines. In practice, nothing involving the FAA is as easy as it looks.

“They told me the FAA couldn’t approve an initial TBO for these engines longer than 1,000 hours,” Jimmy said to me with a sigh. He had just returned from a meeting with representatives from the FAA Aircraft Certification Office and the Engine & Propeller Directorate. “I explained that our engines are virtually identical in all critical design respects to Lycoming engines that have a 2,000-hour TBO, and that every critical part in our engines is PMA approved for use in those 2,000-hour engines.”

“But they said they could only approve a 1,000-hour TBO to begin with,” Jimmy continued, “and would consider incrementally increasing the TBO after the engines had proven themselves in the field. Problem is that nobody is going to buy one of our certified engines if it has only a 1,000-hour TBO, so the engines will never get to prove themselves. It makes no sense, Mike. It’s not reasonable. Not logical. Doesn’t seem fair.”

I certainly understood where Jimmy was coming from. But I also understood where the FAA was coming from.

A brief history of TBO

To quote a 1999 memorandum from the FAA Engine & Propeller Directorate:

The initial models of today’s horizontally opposed piston engines were certified in the late 1940s and 1950s. These engines initially entered service with recommended TBOs of 500 to 750 hours. Over the next 50 years, the designs of these engines have remained largely unchanged but the manufacturers have gradually increased their recommended TBOs for existing engine designs to intervals as long as 2,000 hours. FAA acceptance of these TBO increases was based on successful service, engineering design, and test experience. New engine designs, however, are still introduced with relatively short TBOs, in the range of 600 hours to 1,000 hours.

From the FAA’s perspective, ECi’s Titan engines are new engines, despite the fact that they are virtually clones of engines that have been flying for six decades, have a Lycoming-recommended TBO of 2,000 hours, and routinely make it to 4,000 or 5,000 hours between overhauls.

Is it any wonder we’re still flying behind engine technology designed in the ‘40s and ‘50s? If the FAA won’t grant a competitive TBO to a Lycoming clone, imagine the difficulties that would be faced by a company endeavoring to certify a new-technology engine. Catch 22.

Preparing for an engine test cell endurance run.

Incidentally, there’s a common misconception that engine TBOs are based on the results of endurance testing by the manufacturer. They aren’t. The regulations that govern certification of engines (FAR Part 33) require only that a new engine design be endurance tested for 150 hours in order to earn certification. Granted, the 150-hour endurance test is fairly brutal: About two-thirds of the 150 hours involves operating the engine at full takeoff power with CHT and oil temperature at red-line. (See FAR 33.49 for the gory details.) But once the engine survives its 150-hour endurance test, the FAA considers it good to go.

In essence, the only endurance testing for engine TBO occurs in the field. Whether we realize it or not, those of us who fly behind piston aircraft engines have been pressed into service as involuntary beta testers.

What about a TBO-free engine?

“Jimmy, this might be a bit radical” I said, “but where exactly in FAR Part 33 does it state that a certificated engine has to have a recommended TBO?” (I didn’t know the answer, but I was sure Jimmy had Part 33 committed to memory.)

“Actually, it doesn’t,” Jimmy answered. “The only place TBO is addressed at all is in FAR 33.19, where it says that ‘engine design and construction must minimize the development of an unsafe condition of the engine between overhaul periods.’ But nowhere in Part 33 does it say that any specific overhaul interval must be prescribed.”

“So you’re saying that engine TBO is a matter of tradition rather than a requirement of regulation?”

“I suppose so,” Jimmy admitted.

“Well then how about trying to certify your Titan engines without any TBO?” I suggested. “If you could pull that off, you’d change our world, and help drag piston aircraft engine maintenance kicking and screaming into the 21st century.”

An FAA-inspired roadmap

I pointed out to Jimmy that there was already a precedent for this in FAR Part 23, the portion of the FARs that governs the certification of normal, utility, aerobatic and commuter category airplanes. In essence, Part 23 is to non-transport airplanes what Part 33 is to engines. On the subject of airframe longevity, Part 23 prescribes an approach that struck me as being also appropriate for dealing with engine longevity.

Since 1993, Part 23 has required that an applicant for an airplane Type Certificate must provide the FAA with a longevity evaluation of metallic  wing, empennage and pressurized cabin structures. The applicant has the choice of three alternative methods for performing this evaluation. It’s up to the applicant to choose which of these methods to use:

  • “Safe-Life” —The applicant must define a “safe-life” (usually measured in either hours or cycles) after which the structure must be taken out of service. The safe-life is normally established by torture-testing the structure until it starts to fail, then dividing the time-to-failure by a safety factor (“scatter factor”) that is typically in the range of 3 to 5 to calculate the approved safe-life of the structure. For example, the Beech Baron 58TC wing structure has a life limit (safe-life) of 10,000 hours, after which the aircraft is grounded. This means that Beech probably had to torture-test the wing spar for at least 30,000 hours and demonstrate that it didn’t develop cracks.
  • “Fail-Safe” —The applicant must demonstrate that the structure has sufficient redundancy that it can still meet its ultimate strength requirements even after the complete failure of any one principal structural element. For example, a three-spar wing that can meet all certification requirements with any one of the three spars hacksawed in half would be considered fail-safe and would require no life limitation.
  • “Damage Tolerance” —The applicant must define a repetitive inspection program that can be shown with very high confidence to detect structural damage before catastrophic failure can occur. This inspection program must be incorporated into the Airworthiness Limitations section of the airplane’s Maintenance Manual or Instructions for Continued Airworthiness, and thereby becomes part of the aircraft’s certification basis.

If we were to translate these Part 23 (airplane) concepts to the universe of FAR Part 33 (engines):

  • Safe-life would be the direct analog of TBO; i.e., prescribing a fixed interval between overhauls.
  • Fail-safe would probably be impractical, because an engine that included enough redundancy to meet all certification requirements despite the failure of any principal structural element (e.g., a crankcase half, cylinder head or piston) would almost surely be too heavy.
  • Damage tolerance would be the direct analog of overhauling the engine strictly on-condition (based on a prescribed inspection program) with no fixed life limit. (This is precisely what I have been practicing and preaching for decades.)

How would it work?

SavvyAnalysis chart

Engine monitor data would be uploaded regularly to a central repository for analysis.

Jimmy and I have had several follow-on conversations about this, and he’s starting to draft a detailed proposal for an inspection protocol that we hope might be acceptable to the FAA as a basis of certifying the Titan engines on the basis of damage tolerance and eliminate the need for any recommended TBO. This is still very much a work-in-progress, but here are some of the thoughts we have so far:

  • The engine installation would be required to include a digital engine monitor that records EGTs and CHTs for each cylinder plus various other critical engine parameters (e.g., oil pressure and temperature, fuel flow, RPM). The engine monitor data memory would be required to be dumped on a regular basis and uploaded via the Internet to a central repository prescribed by ECi for analysis. The uploaded data would be scanned automatically by software for evidence of abnormalities like high CHTs, low fuel flow, failing exhaust valves, non-firing spark plugs, improper ignition timing, clogged fuel nozzles, detonation and pre-ignition. The data would also be available online for analysis by mechanics and ECi technical specialists.
  • At each oil-change interval, the following would be required: (1) An oil sample would be taken for spectrographic analysis (SOAP) by a designated laboratory, and a copy of the SOAP reports would be transmitted electronically to ECi; and (2) The oil filter would be cut open for inspection, digital photos of the filter media would be taken, when appropriate the filter media would be sent for scanning electron microscope (SEM) evaluation by a designated laboratory, and the media photos and SEM reports would be transmitted electronically to ECi.
  • At each annual or 100-hour inspection, the following would be required: (1) Each cylinder would undergo a borescope inspection of the valves, cylinder bores and piston crowns using a borescope capable of capturing digital images, and the borescope images would be transmitted electronically to ECi; (2) Each cylinder rocker cover would be removed and digital photographs of the visible valve train components would be transmitted electronically to ECi; (3) The spark plugs would be removed for cleaning/gapping/rotation, and digital photographs of the electrode ends of the spark plugs would be taken and transmitted electronically to ECi; and (4) Each cylinder would undergo a hot compression test and the test results be transmitted electronically to ECi.

The details still need to be ironed out, but you get the drift. If such a protocol were implemented for these engines (and blessed by the FAA), ECi would have the ability to keep very close tabs on the mechanical condition and operating parameters of each its engines—something that no piston aircraft engine manufacturer has ever been able to do before—and provide advice to each individual Titan engine owner about when each individual engine is in need of an overhaul, teardown inspection, cylinder replacement, etc.

Jimmy even thinks that if such a protocol could be implemented and approved, ECi might even be in a position to offer a warranty for these engines far beyond what engine manufacturers and overhaul shops have been able to offer in the past. That would be frosting on the cake.

I’ve got my fingers, toes and eyes crossed that the FAA will go along with this idea of an engine certified on the basis of damage tolerance rather than safe-life. It would be a total game-changer, a long overdue nail in the coffin of the whole misguided notion that fixed-interval TBOs for aircraft engines make sense. And if ECi succeeds in getting its Titan engine certified on the basis of condition monitoring rather than fixed TBO, maybe Continental and Lycoming might jump on the overhaul-on-condition bandwagon. Wouldn’t that be something?

How Do Piston Aircraft Engines Fail?

Wednesday, April 9th, 2014

Last month, I tried to make the case that piston aircraft engines should be overhauled strictly on-condition, not at some fixed TBO. If we’re going to do that, we need to understand how these engines fail and how we can protect ourselves against such failures. The RCM way of doing that is called Failure Modes and Effects Analysis (FMEA), and involves examining each critical component of these engines and looking at how they fail, what consequences those failures have, and what practical and cost-efficient maintenance actions we can take to prevent or mitigate those failures. Here’s my quick back-of-the-envelope attempt at doing that…

Crankshaft

CrankshaftsThere’s no more serious failure mode than crankshaft failure. If it fails, the engine quits.

Yet crankshafts are rarely replaced at overhaul. Lycoming did a study that showed their crankshafts often remain in service for more than 14,000 hours (that’s 7+ TBOs) and 50 years. Continental hasn’t published any data on this, but their crankshafts probably have similar longevity.

Crankshafts fail in three ways: (1) infant-mortality failures due to improper materials or manufacture; (2) failures following unreported prop strikes; and (3) failures secondary to oil starvation and/or bearing failure.

Over the past 15 years, we’ve seen a rash of infant-mortality failures of crankshafts. Both Cnntinental and Lycoming have had major recalls of crankshafts that were either forged from bad steel or were damaged during manufacture. These failures invariably occurred within the first 200 hours after the new crankshaft entered service. If the crankshaft survived its first 200 hours, we can be confident that it was manufactured correctly and should perform reliably for numerous TBOs.

Unreported prop strikes seem to be getting rare because owners and mechanics are becoming smarter about the high risk of operating an engine after a prop strike. There’s now an AD mandating a post-prop-strike engine teardown for Lycoming engines, and a strongly worded service bulletin for Continental engines. Insurance will always pay for the teardown and any necessary repairs, so it’s a no-brainer.

That leaves failures due to oil starvation and/or bearing failure. I’ll address that shortly.

Crankcase halvesCrankcase

Crankcases are also rarely replaced at major overhaul. They are typically repaired as necessary, align-bored to restore critical fits and limits, and often provide reliable service for many TBOs. If the case remains in service long enough, it will eventually crack. The good news is that case cracks propagate slowly enough that a detailed visual inspection once a year is sufficient to detect such cracks before they pose a threat to safety. Engine failures caused by case cracks are extremely rare—so rare that I don’t think I ever remember hearing or reading about one.

Lycoming cam and lifterCamshaft and Lifters

The cam/lifter interface endures more pressure and friction than any other moving parts n the engine. The cam lobes and lifter faces must be hard and smooth in order to function and survive. Even tiny corrosion pits (caused by disuse or acid buildup in the oil) can lead to rapid destruction (spalling) of the surfaces and dictate the need for a premature engine teardown. Cam and lifter spalling is the number one reason that engines fail to make TBO, and it’s becoming an epidemic in the owner-flown fleet where aircraft tend to fly irregularly and sit unflown for weeks at a time.

The good news is that cam and lifter problems almost never cause catastrophic engine failures. Even with a badly spalled cam lobe (like the one pictured at right), the engine continues to run and make good power. Typically, a problem like this is discovered at a routine oil change when the oil filter is cut open and found to contain a substantial quantity of ferrous metal, or else a cylinder is removed for some reason and the worn cam lobe can be inspected visually.

If the engine is flown regularly, the cam and lifters can remain in pristine condition for thousands of hours. At overhaul, the cam and lifters are often replaced with new ones, although a reground cam and reground lifters are sometimes used and can be just as reliable.

Gears

The engine has lots of gears: crankshaft and camshaft gears, oil pump gears, accessory drive gears for fuel pump, magnetos, prop governor, and sometimes alternator. These gears are made of case-hardened steel and typically have a very long useful life. They are not usually replaced at overhaul unless obvious damage is found. Engine gears rarely cause catastrophic engine failures.

Oil Pump

Failure of the oil pump is rarely responsible for catastrophic engine failures. If oil pressure is lost, the engine will seize quickly. But the oil pump is dead-simple, consisting of two steel gears inside a close-tolerance aluminum housing, and usually operates trouble free. The pump housing can get scored if a chunk of metal passes through the oil pump—although the oil pickup tube has a suction screen to make sure that doesn’t happen—but even if the pump housing is damaged, the pump normally has ample output to maintain adequate oil pressure in flight, and the problem is mainly noticeable during idle and taxi. If the pump output seems deficient at idle, the oil pump housing can be removed and replaced without tearing down the engine.

spun main bearingBearings

Bearing failure is responsible for a significant number of catastrophic engine failures. Under normal circumstances, bearings have a long useful life. They are always replaced at major overhaul, but it’s not unusual for bearings removed at overhaul to be in pristine condition with little detectable wear.

Bearings fail prematurely for three reasons: (1) they become contaminated with metal from some other failure; (2) they become oil-starved when oil pressure is lost; or (3) main bearings become oil-starved because they shift in their crankcase supports to the point where their oil supply holes become misaligned (as with the “spun bearing” pictured at right).

Contamination failures can generally be prevented by using a full-flow oil filter and inspecting the filter for metal at every oil change. So long as the filter is changed before its filtering capacity is exceeded, metal particles will be caught by the filter and won’t get into the engine’s oil galleries and contaminate the bearings. If a significant quantity of metal is found in the filter, the aircraft should be grounded until the source of the metal is found and corrected.

Oil-starvation failures are fairly rare. Pilots tend to be well-trained to respond to decreasing oil pressure by reducing power and landing at the first opportunity. Bearings will continue to function properly at partial power even with fairly low oil pressure.

Spun bearings are usually infant-mortality failures that occur either shortly after an engine is overhauled (due to an assembly error) or shortly after cylinder replacement (due to lack of preload on the through bolts). Failures occasionally occur after a long period of crankcase fretting, but such fretting is usually detectable through oil filter inspection and oil analysis).They can also occur after extreme unpreheated cold starts, but that is quite rare.

Thrown Connecting RodConnecting Rods

Connecting rod failure is responsible for a significant number of catastrophic engine failures. When a rod fails in flight, it often punches a hole in the crankcase (“thrown rod”) and causes loss of engine oil and subsequent oil starvation. Rod failure have also been known to cause camshaft breakage. The result is invariably a rapid and often total loss of engine power.

Connecting rods usually have a long useful life and are not normally replaced at overhaul. (Rod bearings, like all bearings, are always replaced at overhaul.) Many rod failures are infant-mortality failures caused by improper tightening of the rod cap bolts during engine assembly. Rod failures can also be caused by the failure of the rod bearings, often due to oil starvation. Such failures are usually random failures unrelated to time since overhaul.

Pistons and Rings

Piston and ring failures usually cause only partial power loss, but in rare cases can cause complete power loss. Piston and ring failures are of two types: (1) infant-mortality failures due to improper manufacturer or assembly; and (2) heat-distress failures caused by pre-ignition or destructive detonation events. Heat-distress failures can be caused by contaminated fuel (e.g., 100LL laced with Jet A), or by improper engine operation. They are generally unrelated to hours or years since overhaul. A digital engine monitor can alert the pilot to pre-ignition or destructive detonation events in time for the pilot to take corrective action before heat-distress damage is done.

Head SeparationCylinders

Cylinder failures usually cause only partial power loss, but occasionaly can cause complete power loss. A cylinder consists of a forged steel barrel mated to an aluminum alloy head casting. Cylinder barrels typically wear slowly, and excessive wear is detected at annual inspection by means of compression tests and borescope inspections. Cylinder heads can suffer fatigue failures, and occasionally the head can separate from the barrel. As dramatic as it sounds, a head separation causes only a partial loss of power; a six-cylinder engine with a head-to-barrel separation can still make better than 80% power. Cylinder failures can be infant-mortality failures (due to improper manufacture) or age-related failures (especially if the cylinder head remains in service for more than two or three TBOs). Nowadays, most major overhauls include new cylinders, so age-related cylinder failures have become quite rare.

Broken Exhaust ValveValves and Valve Guides

It is quite common for exhaust valves and valve guides to develop problems well short of TBO. Actual valve failures are becoming much less common nowadays because incipient problems can usually be detected by means of borescope inspections and digital engine monitor surveillance. Even if a valve fails completely, the result is usually only partial power loss and an on-airport emergency landing.

Rocker Arms and Pushrods

Rocker arms and pushrods (which operate the valves) typically have a long useful life and are not normally replaced at overhaul. (Rocker bushings, like all bearings, are always replaced at overhaul.) Rocker arm failure is quite rare. Pushrod failures are caused by stuck valves, and can almost always be avoided through regular borescope inspections. Even when they happen, such failures usually result in only partial power loss.

Failed Mag Distributor GearsMagnetos and Other Ignition Components

Magneto failure is uncomfortably commonplace. Mags are full of plastic components that are less than robust; plastic is used because it’s non-conductive. Fortunately, our aircraft engines are equipped with dual magnetos for redundancy, and the probability of both magnetos failing simultaneously is extremely remote. Mag checks during preflight runup can detect gross ignition system failures, but in-flight mag checks are far better at detecting subtle or incipient failures. Digital engine monitors can reliably detect ignition system malfunctions in real time if the pilot is trained to interpret the data. Magnetos should religiously be disassembled, inspected and serviced every 500 hours; doing so drastically reduces the likelihood of an in-flight magneto failure.

The Bottom Line

The bottom-end components of our piston aircraft engines—crankcase, crankshaft, camshaft, bearings, gears, oil pump, etc.—are very robust. They normally exhibit long useful life that are many multiples of published TBOs. Most of these bottom-end components (with the notable exception of bearings) are routinely reused at major overhaul and not replaced on a routine basis. When these items do fail prematurely, the failures are mostly infant-mortality failures that occur shortly after the engine is built, rebuilt or overhauled, or they are random failures unrelated to hours or years in service. The vast majority of random failures can be detected long before they get bad enough to cause an in-flight engine failure simply by means of routine oil-filter inspection and laboratory oil analysis.

The top-end components—pistons, cylinders, valves, etc.—are considerably less robust. It is not at all unusual for top-end components to fail prior to TBO. However, most of these failures can be prevented by regular borescope inspections and by use of modern digital engine monitors. Even whey they happen, top-end failures usually result in only partial power loss and a successful on-airport landing, and they usually can be resolved without having to remove the engine from the aircraft and sending it to an engine shop. Most top-end failures are infant-mortality or random failures that do not correlate with time since overhaul.

The bottom line is that a detailed FMEA of piston aircraft engines strongly suggests that the traditional practice of fixed-interval engine overhaul or replacement is unwarranted and counterproductive. A conscientiously applied program of condition monitoring that includes regular oil filter inspection, oil analysis, borescope inspections and digital engine monitor data analysis can yield improved reliability and much reduced expense and downtime.

Do Piston Engine TBOs Make Sense?

Thursday, March 13th, 2014

Last month, I discussed the pioneering work on Reliability-Centered Maintenance (RCM) done by United Airlines scientists Stan Nowlan and Howard Heap in the 1960s, and I bemoaned the fact that RCM has not trickled down the aviation food chain to piston GA. Even in the 21st century, maintenance of piston aircraft remains largely time-based rather than condition-based.

mfr_logo_montageMost owners of piston GA aircraft dutifully overhaul their engines at TBO, overhaul their propellers every 5 to 7 years, and replace their alternators and vacuum pumps every 500 hours just as Continental, Lycoming, Hartzell, McCauley, HET and Parker Aerospace call for. Many Bonanza and Baron owners have their wing bolts pulled every five years, and most Cirrus owners have their batteries replaced every two years for no good reason (other than that it’s in the manufacturer’s maintenance manual).

Despite an overwhelming body of scientific research demonstrating that this sort of 1950s-vintage time-based preventive maintenance is counterproductive, worthless, unnecessary, wasteful and incredibly costly, we’re still doing it. Why?

Mostly, I think, because of fear of litigation. The manufacturers are afraid to change anything for fear of being sued (because if they change anything, that could be construed to mean that what they were doing before was wrong). Our shops and mechanics are afraid to deviate from what the manufacturers recommend for fear of being sued (because they deviated from manufacturers’ guidance).

Let’s face it: Neither the manufacturers nor the maintainers have any real incentive to change. The cost of doing all this counterproductive, worthless, unnecessary and wasteful preventive maintenance (that actually doesn’t prevent anything) is not coming out of their pockets. Actually, it’s going into their pockets.

If we’re going to drag piston GA maintenance kicking and screaming into the 21st century (or at least out of the 1950s and into the 1960s), it’s going to have to be aircraft owners who force the change. Owners are the ones with the incentive to change the way things are being done. Owners are the ones who can exert power over the manufacturers and maintainers by voting with their feet and their credit cards.

For this to happen, owners of piston GA aircraft need to understand the right way to do maintenance—the RCM way. Then they need to direct their shops and mechanics to maintain their aircraft that way, or take their maintenance business to someone who will. This means that owners need both knowledge and courage. Providing aircraft owners both of these things is precisely why I’m contributing to this AOPA Opinion Leaders Blog.

When are piston aircraft engines most likely to hurt you?

Fifty years ago, RCM researches proved conclusively that overhauling turbine engines at a fixed TBO is counterproductive, and that engine overhauls should be done strictly on-condition. But how can we be sure that his also applies to piston aircraft engines?

In a perfect world, Continental and Lycoming would study this issue and publish their findings. But for reasons mentioned earlier, this ain’t gonna happen. Continental and Lycoming have consistently refused to release any data on engine failure history of their engines, and likewise have consistently refused to explain how they arrive at the TBOs that they publish. For years, one aggressive plaintiff lawyer after another have tried to compel Continental and Lycoming to answer these questions in court. All have failed miserably.

So if we’re going to get answers to these critical questions, we’re going to have to rely on engine failure data that we can get our hands on. The most obvious source of such data is the NTSB accident database. That’s precisely what brilliant mechanical engineer Nathan T. Ulrich Ph.D. of Lee NH did in 2007. (Dr. Ulrich also was a US Coast Guard Auxiliary pilot who was unhappy that USCGA policy forbade him from flying volunteer search-and-rescue missions if his Bonanza’s engine was past TBO.)

Dr. Ulrich analyzed five years’ worth of NTSB accident data for the period 2001-2005 inclusive, examining all accidents involving small piston-powered airplanes (under 12,500 lbs. gross weight) for which the NTSB identified “engine failure” as either the probable cause or a contributing factor. From this population of accidents, Dr. Ulrich eliminated those involving air-race and agricultural-application aircraft. Then he analyzed the relationship between the frequency of engine-failure accidents and the number of hours on the engine since it was last built, rebuilt or overhauled. He did a similar analysis based on the calendar age of the engine since it  was last built, rebuilt or overhauled. The following histograms show the results of his study:

Ulrich study (hours)

Ulrich study (years)

If these histograms have a vaguely familiar look, it might be because they look an awful lot like the histograms generated by British scientist C.H. Waddington in 1943.

Now,  we have to be careful about how we interpret Dr. Ulrich’s findings. Ulrich would be the first to agree that NTSB accident data can’t tell us much about the risk of engine failures beyond TBO, simply because most piston aircraft engines are voluntarily euthanized at or near TBO. So it shouldn’t be surprising that we don’t see very many engine failure accidents involving engines significantly past TBO, since there are so few of them flying. (The engines on my Cessna 310 are at more than 205% of TBO, but there just aren’t a lot of RCM true believers like me in the piston GA community…yet.)

What Dr. Ulrich’s research demonstrates unequivocally is striking and disturbing frequency of “infant-mortality” engine-failure accidents during the first few years and first few hundred hours after an engine is built, rebuilt or overhauled. Ulrich’s findings makes it indisputably clear that by far the most likely time for you to fall out of the sky due to a catastrophic engine failure is when the engine is young, not when it’s old.

(The next most likely time for you to fall out of the sky is shortly after invasive engine maintenance in the field, particularly cylinder replacement, but that’s a subject for a future blog post…stay tuned!)

 So…Is there a good reason to overhaul your engine at TBO?

Engine overhaulIt doesn’t take a rocket scientist (or a Ph.D. in mechanical engineering) to figure out what all this means. If your engine reaches TBO and still gives every indication of being healthy (good performance, not making metal, healthy-looking oil analysis and borescope results, etc.), overhauling it will clearly degrade safety, not improve it. That’s simply because it will convert your low-risk old engine into a high-risk young engine. I don’t know about you, but that certainly strikes me as a remarkably dumb thing to do.

So why is overhauling on-condition such a tough sell to our mechanics and the engine manufacturers? The counter-argument goes something like this: “Since we have so little data about the reliability of past-TBO engines (because most engines are arbitrarily euthanized at TBO), how can we be sure that it’s safe to operate them beyond TBO?” RCM researchers refer to this as “the Resnikoff Conundrum” (after mathematician H.L. Resnikoff).

To me, it looks an awful lot like the same circular argument that was used for decades to justify arbitrarily euthanizing airline pilots at age 60, despite the fact that aeromedical experts were unanimous that this policy made no sense whatsoever. Think about it…

Roots of Reliability-Centered Maintenance

Tuesday, February 11th, 2014

Last month, I discussed the pioneering WWII-era work of the eminent British scientist C.H. Waddington, who discovered that the scheduled preventive maintenance (PM) being performed on RAF B-24 bombers was actually doing more harm than good, and that drastically cutting back on such PM resulted in spectacular improvement in dispatch reliability of those aircraft. Two decades later, a pair of brilliant American engineers at United Airlines—Stan Nowlan and Howard Heap—independently rediscovered the utter wrongheadedness of traditional scheduled PM, and took things to the next level by formulating a rigorous engineering methodology for creating an optimal maintenance program to maximize safety and dispatch reliability while minimizing cost and downtime. Their approach became known as “Reliability-Centered Maintenance” (RCM), and revolutionized the way maintenance is done in the airline industry, military aviation, high-end bizjets, space flight, and numerous non-aviation applications from nuclear power plants to auto factories.

RCM wear-out curve

The traditional approach to PM assumes that most components start out reliable, and then at some point start becoming unreliable as they age

The “useful life” fallacy

Nowlan and Heap showed the fallacy of two fundamental principles underlying traditional scheduled PM:

  • Components start off being reliable, but their reliability deteriorates with age.
  • The useful life of components can be established statistically, so components can be retired or overhauled before they fail.

It turns out that both of these principles are wrong. To quote Nowlan and Heap:

“One of the underlying assumptions of maintenance theory has always been that there is a fundamental cause-and-effect relationship between scheduled maintenance and operating reliability. This assumption was based on the intuitive belief that because mechanical parts wear out, the reliability of any equipment is directly related to operating age. It therefore followed that the more frequently equipment was overhauled, the better protected it was against the likelihood of failure. The only problem was in determining what age limit was necessary to assure reliable operation. “In the case of aircraft it was also commonly assumed that all reliability problems were directly related to operating safety. Over the years, however, it was found that many types of failures could not be prevented no matter how intensive the maintenance activities. [Aircraft] designers were able to cope with this problem, not by preventing failures, but by preventing such failures from affecting safety. In most aircraft essential functions are protected by redundancy features which ensure that, in the event of a failure, the necessary function will still be available from some other source.

RCM six curves

RCM researchers found that only 2% of aircraft components have failures that are predominantly age-related (curve B), and that 68% have failures that are primarily infant mortality (curve F).

“Despite the time-honored belief that reliability was directly related to the intervals between scheduled overhauls, searching studies based on actuarial analysis of failure data suggested that the traditional hard-time policies were, apart from their expense, ineffective in controlling failure rates. This was not because the intervals were not short enough, and surely not because the tear down inspections were not sufficiently thorough. Rather, it was because, contrary to expectations, for many items the likelihood of failure did not in fact increase with increasing age. Consequently a maintenance policy based exclusively on some maximum operating age would, no matter what the age limit, have little or no effect on the failure rate.”

[F. Stanley Nowlan and Howard F. Heap, “Reliability-Centered Maintenance” 1978, DoD Report Number AD-A066579.]

Winning the war by picking our battles

FMEAAnother traditional maintenance fallacy was the intuitive notion that aircraft component failures are dangerous and need to be prevented through PM. A major focus of RCM was to identify the ways that various components fail, and then evaluate the frequency and consequences of those failures. This is known as “Failure Modes and Effects Analysis” (FMEA). Researchers found that while certain failure modes have serious consequences that can compromise safety (e.g., a cracked wing spar), the overwhelming majority of component failures have no safety impact and have consequences that are quite acceptable (e.g., a failed #2 comm radio or #3 hydraulic pump). Under the RCM philosophy, it makes no sense whatsoever to perform PM on components whose failure has acceptable consequences; the optimal maintenance approach for such components is simply to leave them alone, wait until they fail, and then replace or repair them when they do. This strategy is known as “run to failure” and is a major tenet of RCM.

A maintenance revolution…

Jet airliner

The 747, DC-10 and L-1011 were the first airliners that had RCM-based maintenance programs.

As a direct result of this research, airline maintenance practices changed radically. RCM-inspired maintenance programs were developed for the Boeing 747, Douglas DC-10 and Lockheed L-1011, and for all subsequent airliners. The contrast with the traditional (pre-RCM) maintenance programs for the Boeing 707 and 727 and Douglas DC-8 was astonishing. The vast majority of component TBOs and life-limits were abandoned in favor of an on-condition approach based on monitoring the actual condition of engines and other components and keeping them in service until their condition demonstrably deteriorated to an unacceptable degree. For example, DC-8 had 339 components with TBOs or life limits, whereas the DC-10 had only seven—and none of them were engines. (Research showed clearly that overhauling engines at a specific TBO didn’t make them safer, and actually did the opposite.) In addition, the amount of scheduled maintenance was drastically reduced. For example, the DC-8 maintenance program required 4,000,000 labor hours of major structural inspections during the aircraft’s first 20,000 hours in service, while the 747 maintenance program called for only 66,000 labor hours, a reduction of nearly two orders of magnitude.

Greybeard AMTs.

Owner-flown GA, particularly piston GA, is the only remaining segment of aviation that does things the bad old-fashioned way.

Of course, these changes saved the airlines a king’s ransom in reduced maintenance costs and scheduled downtime. At the same time, the airplanes had far fewer maintenance squawks and much better dispatch reliability. (This was the same phenomenon that the RAF experienced during WWII when they followed Waddington’s advice to slash scheduled PM.)

…that hasnt yet reached piston GA

Today, there’s only one segment of aviation that has NOT adopted the enlightened RCM approach to maintenance, and still does scheduled PM the bad old-fashioned way. Sadly, that segment is owner-flown GA—particularly piston GA—at the bottom of the aviation food chain where a lot of us hang out. I’ll offer some thoughts about that next month.