Continuing Ed: Hands On

Learning to fly is all about acquiring a new body of knowledge, developing a new set of skills, and embracing a philosophy that says safety is primary. Overall, flight instructors and students do a good job of meeting those goals, at least as far as operating the aircraft is concerned. Where our pilot education falls short is in the mechanical side of things. Sure, we take a quick academic look beneath the smooth skin of a general aviation aircraft, but in general, our knowledge and understanding of what goes on is limited.

Just as we combine academic study of the theory of flight with hands-on instruction in the cockpit, perhaps we should be combining academic study of the mechanics of an aircraft with hands-on wrenching of cylinders, airframe access plates, and main electrical busses.

Why? Knowledge is its own reward, and a pilot armed with a working knowledge of the aircraft is in a better position to prevent mechanical problems, and deal with problems if they do occur.

I?m not advocating a change to pilot training regulations to require intensive mechanical instruction in aircraft and the addition of practical test standards. My point is that gaining an insider?s knowledge of the mechanical workings of aircraft can only help a pilot achieve a higher level of flying skill and performance.

Gaining a mechanical education becomes even more important when you become an aircraft owner. When you own it, you want to know more about it. The desire to ensure the maximum level of safety is joined by a new motivation ? cost. You can save money. If you know how your airplane works, and how to keep it working as it should, you?re ahead of the unscheduled maintenance game.

I?ve been attending the practical school of aircraft maintenance since I bought a Cessna 172 about six years ago. My first course was sitting in on the annual inspection that came due a couple of months after I bought the airplane. Actually, I did more than just watch. I opened all the inspection portals on the fuselage, wing, and tail so the mechanic could peer in and shine his flashlight around the aluminum stringers, formers, ribs, bulkheads, and skins like a doctor looking down my throat for who knows what.

Participating in an annual inspection is a great way to learn about an airplane. I removed the seats and carpeting to expose the bare-aluminum floor so I could remove more inspection plates. This exposed the flight control cables running from the control yokes to the control surfaces. I could see the pulleys and bellcranks the engineers designed to make the cable system work reliably over years of service. Removing the flimsy bulkhead at the aft end of the baggage compartment exposed the converging tunnel of the aft fuselage, and the business end of the elevator, pitch trim, and rudder flight control system.

It turned out that the pulleys in the aft fuselage hadn?t been lubricated consistently, and some were frozen. That meant the cables were grinding across the stationary pulley wheels, resulting in excessive cable wear. Seeing the problem, rather than being told about it as I received the inspection and repair invoice, made a lasting impression on me.

Two of the four seat rails had to be replaced because the seat-pin holes were elongated from use. The mechanic had to do this job. But seeing the rails? condition sure made me aware that I had to take a careful approach to positioning the airplane?s front seats, both to ensure that the pins were locked in place, and to avoid excessive wear.

I removed the wheels and brakes, installed a new tire and new brake pads, cleaned and re-packed the wheel bearings, and put all the pieces back together. After I had replaced all three tires, I think that doing the work myself gave me a much better appreciation for why it?s important to avoid flat-spotting the tires and riding the brakes.

I sold the Cessna last year, and became a partner in a light twin. Since then my mechanical education has accelerated, mostly because my partner has a great working relationship with an accomplished mechanic who encourages us to get hands on with the airplane. He provides instruction, advice, special tools when and where needed, supervision, quality control, and post-wrenching inspection. My partner and I don?t do all of the work on the airplane, but we do as much as is possible, practical, and safe.

A few weeks ago I completed an advanced course when I attacked a cylinder that had been weeping oil. Oil consumption wasn?t the issue ? it was well within acceptable limits ? but the greasy mess the leak created on the bottom of the engine and wing was bothersome and embarrassing to say the least. The leak wasn?t going to fix itself, so the only option was to dig in and get dirty.

The repair project began with disconnecting the cowl flaps and removing six separate cowling pieces that enclose the engine. Then the fun began. We had to prepare the cylinder for removal by disconnecting an intricate network of metal and flexible hoses, pipes, cables, and lines. It?s not unlike disassembling a puzzle in which the interlocking pieces must be removed in a specific order.

With all the peripheral items removed, we loosened the nuts holding the cylinder down, and carefully pulled it out. The huge piston slid out from the cylinder barrel, and suddenly the very core of the engine was revealed in the yawning open circle in the engine block.

For all the precision, minute tolerances, and careful engineering embodied in aircraft engines, I couldn?t help but think that this four-cylinder, normally aspirated, fuel-injected powerplant was basically a piece of heavy industry. The rough-hewn crankcase visible through the block was huge, imposing. There is nothing subtle or fragile about the business end of an aircraft engine. It?s no wonder, either, given the temperatures and pressures these engines must endure without fail.

Looking at the engine partially exposed, I gained a new appreciation for how aircraft powerplant designers and manufacturers achieve the performance and reliability that pilots and passengers demand. In a word, it?s mass.

The leak turned out to be caused by some grit lining the lower lip of the flange where an O-ring on the base of the cylinder sits. The O-ring provides the seal that keeps oil from leaking between the engine block and the cylinder base. Over time the grit had worked its way past the seal, and oil followed.

We cleaned the area, slipped a new O-ring onto the base of the cylinder, and worked the cylinder back over the piston and rings. That was just one of the tasks handled exclusively by the mechanic. It takes experience to position the rings so they make the best possible seal inside the cylinder chamber, and then slide the piston-ring assembly up into the cylinder.

That done, we began re-assembling the puzzle in the reverse order that we removed it. About 90 minutes later we were done, ready to run the engine. If there is a sight as sweet as an oil-free engine block after removing and replacing a cylinder and firing the thing up, I don?t know what it would be.

I?ve trashed several pairs of jeans and T-shirts removing cowlings, changing oil, replacing worn hoses, and, now, replacing a cylinder base O-ring on our airplane. The clothes are replaceable; the knowledge and satisfaction I?ve gained isn?t.