Fly the Engine: Second Edition

By Kas Thomas

Revised 2008 edition!Back in print for the first time in over a decade! Fully revised and updated. The ultimate book on aircraft engine operation, Fly the Engine takes you through all phases of engine operation, from preflight to shutdown. Learn how to start a hot, cold, or flooded engine; how to troubleshoot a rough runup; when and how to lean the engine for all phases of flight; how to recognize the early warning signs of valve sticking; and much more. Every chapter of Fly the Engine brims with hands-on advice, told with wit and style by one of aviation's most respected authors. Hailed as a modern-day classic when it first appeared in 1993, Fly the Engine is a goldmine of engine wisdom: essential reading for any pilot, of any skill level. Great gift item!

• Language: English
• Publisher: Lulu.com
• Release date: Mar 17, 2011
• ISBN: 9781257113590

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Fly the Engine

Kas Thomas

© 2007, 2008 by Kas Thomas.

All rights reserved.

For information about bulk pricing, or permission to reprint portions of this work, write to [e-mail]. Visit us online at http://flytheengine.blogspot.com/

Additional copies of this book can be ordered online through Lulu.com

Rev. 2.0.1, 9 October 2007

For Rita, Mallory, and Justin

Preface to the First Edition

The problem, in a nutshell, is this. A would-be pilot can earn his or her wings in 40 hours. Getting a multiengine rating takes only 10 hours (or less). A complex aircraft checkout (for a pilot moving, say, from a Cessna 172 to a Turbo Lance) requires just a couple of hours. But it only takes a few seconds to ruin a $25,000 engine.

I can assure you, there is no way anybody can become an expert (or even reasonably proficient) in EGT analysis, mag-drop interpretation, cold-start techniques, hot-starts with a fuel-injected engine, cruise-climb leaning, suppressing turbo bootstrapping, knowing when to use alternate air, recognizing morning sickness, troubleshooting mag problems in flight, etc., in just a few hours.

I wish there had been a book like this when I first began flying complex aircraft in 1969. By the time I bought my first airplane (a Skylane) in 1977, I was still very much a neophyte in engine matters. When my 182 began using oil (a quart an hour, ultimately). I started paying attention to questions of engine design, repair processes. and operating techniques that might improve my chances of making TBO (the manufacturer’s recommended Time Between Overhauls). I started going to fly-ins and trade shows. I bought the Continental engine operator’s handbook for my engine—then the overhaul manual. I visited with industry experts, became active in owner organizations, took notes as my engine was top-overhauled. Eventually, by the time I bought my second airplane (a Cessna Turbo 310R), terms like fuel injector nozzle and hydraulic lifter actually began to make sense. The fog began to lift.

Sad to say, most pilots continue to fly in restricted visibilities.

This book is for all pilots, of all skill levels. I particularly hope that it finds an audience among flight instructors. In biennial flight reviews, I have been asked many times to explain the arcane markings on sectional charts (despite the fact that I stopped flying with sectionals years ago). I have never been asked to explain the early warning signs of valve sticking, or how to lean an engine by reference to EGT. Maybe if enough CFIs read this book, that will change.

Some readers will want to know how this book differs from an earlier work of mine, The Aircraft Engine Operating Guide. I wrote the latter book in 1984. Since then, I have flown behind many new (to me) engine types, including the Continental TSIO-520-B, -NB, and -DB, and the Lycoming O-360-E, HIO-360-E, O-540-K. TIO-540-C and TIO-540-J; I have installed and/or flown behind new EGT systems, ranging from a single-probe KSA to GEM 603 and EDM-700; and I have started a new bimonthly journal devoted entirely to aircraft-engine topics (TBO Advisor). The difference between my earlier engine book and this one is thus nine years of flying, nine years of visiting engine shops, nine years of talking to other pilots (troubleshooting their engine problems, etc.), and nine years of writing about engines for Light Plane Maintenance. TBO Advisor. and General Aviation News & Flyer. A lot’s changed in my understanding of FWF matter, and I wanted to write some of it down before I forgot it.

Besides which, pilots have told me repeatedly they need more information, not less. on the subject of engines. (No one has ever come up to me at Oshkosh and said. "Kas. enough about engines. already! How about more on dope and fabric?")

In writing this book. I have drawn on the combined wisdom of many individuals. I would particularly like to thank Peter Bates, Phil Boob, J. R. (Zoom) Campbell, Gary Garvens, Gary Greenwood, Al Hundere, Sandra McDonough, Jack Riley, Jr., Ed Salmeron, Victor Sloan, Joe Sullivan, and John Youngquist; my primary flight instructor, Mary Hanson Hirsch (now with FAA in Ft. Lauderdale); my father, Robert E. Thomas; the many mechanics I’ve dealt with over the years; all the great people at Teledyne Continental and Textron Lycoming; and. of course. my wife, Rita. Thanks, too, to the many hundreds of Light Plane Maintenance and TBO Advisor readers who have shared their engine problems with me over the years. Your efforts have made this possible.

Kas Thomas

Stamford, Connecticut

March 22. 1993

Preface to the Second Edition

When the first edition of this book came out in 1993, pilots had very little to read on the subject of how to operate an aircraft engine; they needed something more than 30-year-old reprints of Lycoming Flyer articles or the meager advice given in Pilots’ Operating Handbooks. They still do. That, in a nutshell, is why I decided to do a Second Edition of this book.

This edition represents a page-by-page overhaul of the original book. As with any good overhaul, I judiciously kept what still worked and junked anything else. Some discussions were deleted; others were expanded or added. Hardly a page in this book hasn’t changed in some way—large or small—since the original edition. And there’s a considerable amount of brand-new material (resulting in 20% more pages).

In many instances, I’ve had to update earlier discussions based on things I’ve learned in the 15 years or so since writing the first edition. Probably the most noticeable example of this is the discussion of shock cooling. I won’t say flat-out that shock cooling is a total myth, but I’m a good deal more skeptical now than when I first wrote the book. In 1993, I was a bit more accepting of anecdotal data (not to mention manufacturers’ handed-down wisdom) than I am today. Cylinder-head cracking was at epidemic proportions in 1993, and it seemed only too reasonable, back then, that shock cooling was playing a significant role somehow. When I began looking for hard evidence, however, I found that (as with stories of alien abduction) the prevailing wisdom was based on very little. In fact it was based entirely on speculation. I now believe (based on the evidence) that shock cooling may play a role in valve sticking, but plays no demonstrable role in cylinder-head cracking. I’ll be glad to change my mind on this when someone can show me a repeatable procedure for getting a cylinder head to crack— whether in a test cell, or in an airplane—by means of shock cooling.

I might add that most of the cylinders that were cracking in 1993 were produced in the 1960s, 1970s, or 1980s, when manufacturing techniques were nowhere near as good as they are today. I have to wonder if those older cylinders would have eventually cracked no matter what pilots did or didn’t do in the cockpit.

In the preface to the first edition I thanked a huge number of people. I need to thank an even bigger number now. I now need to include the tens of thousands of pilots who have bought my publications over the years, particularly the early subscribers to Light Plane Maintenance and TBO Advisor, and anyone who ever bought one of my books. That includes you.

I feel an especially keen sense of gratitude to certain individuals (good friends all) who have passed away since the first edition of this book came out. Those individuals include Ken Brock, Scott Crossfield, Al Hundere, and my father, Robert E. Thomas. Each of these truly exceptional individuals made enormous contributions to my growth as a person and as a pilot. I’m fortunate to have had them in my life.

Three other special people made this book possible, namely my wife Rita; daughter Mallory (now in college); and 13-year-old son Justin. This book is for them.

Kas Thomas

9 October 2007

Part 1: The Basics

1: Preflight

For years, I performed preflight inspections in more or less the usual checklist fashion, as my instructors had taught me over the years, without worrying too much about things that weren’t on the checklist. I figured if I followed the checklist (or my memory of it) religiously, there wasn’t much else to worry about. Anything not on the checklist was out of my control.

My view of prefight inspections changed a number of years ago after an incident that almost cost the life of a dear friend. I was anxious to take my friend’s plane (a Piper Turbo Arrow) on a short trip; the plane was on leaseback with the local flying club, and I decided to rent it one day. But as luck would have it, there was oil leaking from the engine compartment. I had to reject the preflight. I wrote up the oil leak and took the keys and clipboard back to the office.

A few days later, the same airplane threw a connecting rod in flight while my friend (the owner) was on a solo business trip. Oh my God, I muttered to myself when I heard the news. That could’ve been me.

That’s when it finally sank in. After years of doing preflights in mindless, robotic, ritualistic fashion, it suddenly became clear to me that the whole purpose of the preflight inspection is not to satisfy FAA regulations or your flight instructor, or the insurance company, or the FBO; it’s not to avoid embarrassment (because you left the gust lock in, or a wheel chock in front of the nose wheel, or a Pitot-cover on, or a fuel cap off, or the baggage door open—or maybe the towbar hanging from the nosegear—before you started the engine); it’s not to show respect for a time-honored aviator’s ritual, or to pass time while the line boy tops off your fuel tanks. I know now what the purpose of a preflight inspection is. The purpose of the preflight inspection is to keep the airplane from killing me needlessly.

I learned something else from the Turbo Arrow experience. I learned that the engine compartment should get at least as much attention as flight controls, fuel sumps, or any other part of the airplane during walkaround. Particularly if the airplane is not owned and operated (and exclusively flown) by you.

Sandy’s Turbo Arrow was owned by her, but unfortunately, it was leased back to a club, and an unknown number of pilots (with unknown experience levels) would routinely fly the airplane up and down the East Coast, with or without a decent preflight. My own checkout in the airplane (this still amazes me to this day) consisted of the manager of the club handing me the keys and telling me to spend a few minutes reading the Pilot’s Operating Handbook! (He knew that I had plenty of previous turbocharged-engine time, but what he didn’t appreciate is that the Turbo Arrow’s fixed-wastegate system bears no relationship to the other, more forgiving turbo controller systems with which I was familiar)

Other club pilots were flying this airplane immediately before and not long after I wrote it up for oil in the engine compartment. The plane was dripping so much oil that it was running out the bottom of the cowl onto the top of the nosewheel tire. Why the club chose not to look into the cause of the leak is a mystery.

In any case, as I say,. a few days after I wrote the plane up for oil leakage, the Turbo Arrow was back in the air, and my friend Sandy, the plane’s owner, was at the controls, IFR on top, when the oil pressure went south and the No. 1 connecting rod went north. With great piloting skill and some help from Air Traffic Control, Sandy was able to descend through a thick overcast and guide the powerless plane to a no-damage on-airport landing.

Wake-Up Call No. 2

Another preflight experience that somewhat raised my consciousness on this whole subject happened in upstate Wisconsin a number of summers ago, when I was returning from a speaking engagement. It was a hazy, humid afternoon, and my copilot (Jeff Parnau) and I were quite anxious to fire up the Turbo 310 and get going. But as hot and sweaty and anxious-to-get-going as we were, I wasn’t about to cut the preflight short by skipping the aerobics-workout portion of the preflight. I had a longstanding practice of always turning the props over by hand (through 720 degrees of rotation) as part of each and every preflight, to check for cylinder compression and listen for any unusual noises. (This requires a certain amount of upper body strength on a plane like a Turbo 310, particularly if the engines are still hot.and the cylinders have good compression.) The plane, in this particular case, was not tied down. We were on open grass.

Fortunately, very fortunately, the right engine did not fire as I pulled it through (the resulting kickback would probably dislocated my arm, or worse). But it easily could have. After reaching the runup area, we learned that the engine had a broken primary-lead (or P-lead), and therefore a hot mag, on the right engine. This was evident from the fact that there was no rpm drop at all upon switching to left-mag-only operation.

Overcoming Denial

Low-time pilots tend to underappreciate the importance of the preflight inspection, particularly as it applies to the engine compartment. I’ve often thought this to be due just to inexperience, or maybe to the somewhat cavalier attitude conveyed (perhaps unintentionally) by young flight instructors. But over the years, I have witness countless older, more experienced pilots performing what I call kneejerk preflights, oblivious to what they were doing. Consequently, I have developed a theory, which is that pilots, as a rule, are in a mental state of denial where their engines (and airframes) are concerned. Rather than assume the worst on walkaround, the natural inclination of many pilots is to assume the best—to assume that everything will be perfectly normal (because it usually is, and it’s supposed to be, after all).

The tendency to assume the best is a natural tendency—a natural coping strategy—among those who regularly take calculated risks. When one boards a roller coaster at a theme park, one does so in the belief that the coaster is going to stay on the tracks, not accidentally rip free and send passengers hurtling into space. We know that roller coasters are not 100% safe (everybody has a favorite story about an amusement-park disaster of some kind), but we trust that the theme park has adequate systems and procedures in place to ensure the safety of its equipment and we have faith that appropriately trained personnel have done their jobs properly before we step aboard the roller coaster. We step aboard, in other words, assuming the best.

Airline passengers do the same thing, of course. Anyone getting on an airline flight knows full well that airline travel is not 100% safe. But passengers also know the odds are overwhelmingly in favor of a given flight being noneventful, so when getting aboard a large passenger jet most of us check our fears at the gate.

By the time you begin your first flying lesson, you’ve probably been on many airline flights. Therefore it’s natural to bring a certain amount of airline passenger mentality to the occasion. On one’s first flying lessons, the preflight walkaround is closely supervised, generally speaking; the student trusts that the instructor will spot any potential problems that a student could be forgiven for not noticing. Likewise, the student is confident that FAA certified mechanics, working under the auspices of the flight school (or FBO or club), have maintained the training airplanes according to industry accepted procedures and that it is sure to be in sound working order; any defects found on walkaround are likely either to be minor, or something easily spotted, etc. In short, the student (despite the instructor’s remarks, if any, about the importance of the preflight inspection) can be forgiven for going into his or her first few flying lessons with a basic assumption that things will turn out fine. If we didn’t assume this, none of us would ever get onboard an airplane. None of us would ever drive cars, ride elevators, eat raw shellfish, or walk across the street. Risk is all around us. We do our best to put it out of our minds. It’s necessary, at some point, to stop thinking about it. Some people prefer never to think about it at all.

People who confront serious risks on a regular basis (soldiers, law enforcement personnel, fire fighters, race-car drivers, and others in high-risk jobs) have a unique attitude toward risk. They confront risk head-on and never assume that things will go right. They want and expect things to go right, obviously, but safety is never assumed. It’s something that takes deliberate effort.

Step Number One in making safety happen is to confront risks honestly and openly. Admit they exist. Take stock of them. Get to know all you can about them.

The opposite of Step One is called denial.

Step Number Two is to assume ownership of risks so you can manage them.

Step Three is active risk mitigation.

Risk mitigation means applying known risk reduction techniques to a given situation in a disciplined, conscientious fashion.

Professionals whose lives depend (literally) on a piece of hardware working correctly tend to spend a lot of time inspecting and maintaining that hardware. This is risk mitigation in action. A soldier, for example, spends a lot of time cleaning and inspecting his rifle. He doesn’t assume that it will work when needed. Quite the opposite. The assumption is that the weapon will get dirty in service and jam at the worst possible moment.

Likewise, when you are preflighting an aircraft (particularly one that is not solely owned and operated by you), you should assume that today might not be your lucky day. You should assume, in fact, that today is the day bees visited your Pitot tube and plugged it with beeswax, potentially rendering the airspeed indicator inoperative (something that once happened to me). You should assume that today is the day one of your magnetos has a broken P-lead and the engine could fire as you pull the propeller through. You should assume that any oil dripping from the bottom of the engine cowl might be coming from a cracked cylinder head and that today may be the day the head decides to come off in flight.

A favorite activity of the British flying clubs (and others) is to stage mock preflights with airplanes that have purposely been altered in some mischievous fashion, in any of 10 or 20 different ways (for example, to have crossed controls, water in the tanks, control locks in place, a spark plug wire disconnected, and so forth). A consistent finding is that the majority of pilots miss at least one life-threatening defect. My own feeling is that many of the pilots who missed defects actually did see them but took no action because their minds blocked out what they saw. Their conscious mind did not allow the defect to be real.

I was guilty of this on one occasion myself. I was pulling a prop through on my 310 one day and noticed what seemed like a longer-than-normal turn of the prop to reach max compression on a particular cylinder, almost as if the preceding cylinder gave no resistance (no compression hump). I turned the prop all the way through all six compression humps again just to be sure. But this time, there was plenty of compression in each cylinder (plenty of resistance getting past top dead center). To be doubly sure, I pulled the prop through another two full revolutions, and again, I got six strong compression humps. I shrugged and went off to fly, never giving it a second thought.

The flight went without a hitch. Absolutely no evidence of anything out of the ordinary.

A week later, the plane was in the shop for its annual inspection. I soon got a phone call to come down and look at something. The mechanic had one rocker cover off a cylinder. Inside the rocker cover was a small pile of fine metal particles. The mechanic showed me where the valve guide for the exhaust valve had pulled loose from the cylinder head and was going up and down with the valve.

The way I found this, the mechanic explained to me, was that while I was doing the compression check on this cylinder, I got a zero-compression reading. So I turned the prop through and tried again— and got 72/80. (A normal reading.) We decided to take the rocker cover off, and this is what we found.

The reason the compression would alternately be zero and 72 psi is that the springs that pull the valve closed are very strong, and the valves (which have a tapered head) tend to center themselves in their seats as they close. So even though the guide was rattling around on the stem, allowing the valve to cock over now and then, nevertheless the strong spring pressure (combined with the tapered valve face and bevel-cut seat geometry) caused the valve to want to seat straight up and down most of the time, in which case the combustion chamber would seal airtight with no leakage. But every once in a while, the valve would cock over slightly, raising one edge off the seat, allowing air to leak out of the cylinder on the piston’s upstroke. Hence, zero compression every once in a while.

It wasn’t until the mechanic called me during this annual inspection that I remembered my preflight of the week before—the one in which I thought I had felt the prop go past a jug with no compression resistance. I had put it out of my mind, because on that day, as I pulled the prop through a second time to doublecheck, the problem went away, just as I subconsciously wanted it to. In other words, I had seen (and felt) the problem with my own eyes and hands—but quickly dismissed it. I went ahead and flew the airplane anyway, in total disregard of what I should have known was a very real and potentially hazardous mechanical defect.

I hear similar stories all the time. Pilots of turbocharged planes complain of poor performance weeks or months after the turbocharger has stopped working (and ask their mechanics why they aren’t getting the takeoff power they used to get); I’ve heard this one several times. Skylane owners fly with half-a-quart-an-hour oil consumption year after year, thinking the burn rate will improve with time if I just continue to run it hard. Operators of small Lycomings continue to run an engine that starts poorly and shakes badly on the first start of the day but then smoothes out after it has warmed up (a classic sign of valve sticking). Mag drops of 200 or 300 rpm are ignored as if it were nothing. (It’s been that way for a while, what’s the harm in flying it again today?) There’s dark oil in the bottom of the cowling. Never mind, it’s just seepage.

My favorite story is the one about the Aero Commander Shrike owner who pulled into the shop one day to complain about the airplane being out-of-rig. I had to fly all the way over here with the rudder trim pegged all the way to the left, the owner griped, muttering that the mechanics who had just performed the plane’s annual inspection must have somehow misrigged the rudder. A cursory runup showed that the plane’s right engine was running poorly on the ground and would not accelerate past 1,800 rpm. Upon opening the cowling, it was found that the spark plug wires for an entire bank of cylinders were dangling loose. Either somebody had forgotten to hook them back up at the conclusion of the annual inspection, or they were only finger tight to begin with an simply vibrated loose in flight. In any case, the plane’s right engine was firing on only three cylinders. Yet the pilot thought he had a trim problem!

The point is, denial takes many forms. In any of its forms, it is a potential killer.

The first step in performing a good preflight is to counteract denial. And the first step in counteracting denial is to admit that it exists.

I don’t advocate that every pilot adopt my particular stance on preflights (which is to say to myself continuously: This piece of s#!+ is going to try to kill me, if I let it…), but you definitely should do some mental exercises before walking out to the ramp. Start by tuning out your passengers, onlookers, line personnel, and anything else— clear your mind so that you can really see the airplane when you look at it. Adopt a mental attitude that you are going to find whatever is wrong with the airplane. And expect today to be the day when something is wrong with it. Don’t walk around the plane with headphones on, listening to your iPod. Don’t talk on the cell phone. Don’t chat with the fuel attendant. Tolerate no interruptions. If you find yourself being interrupted, zoning out or daydreaming about a personal (or business) problem, trying to remember if you packed a toothbrush, etc., back up a few steps and repeat what you were just doing. Talk to yourself as you do the inspection, if that helps.

Perform a preflight as if your life depended on it. Because guess what? It does.

Water Contamination

Two friends of mine have nearly been killed by water in the fuel. In one instance, the airplane in question (a Decathlon) had recently been fueled from an underground tank that, unbeknownst to anyone at the time, contained many gallons of condensate (water) at the bottom. For whatever reason, the Decathlon’s fuel checked clean on walkaround.