What Breaks And Wears Out First

It sounds logical to assume that an active aircraft will wear out before an inactive one. For some componentsthat is correct, but for others it's not.

Pilots who are purchasing their first airplane probably are curious about what parts are likely to break or wear out first. This is a difficult question to answer precisely because it depends on the airplane and how and where the owner flies it, but a few general guidelines apply to virtually all aircraft.

One thing that has a significant bearing on what will break or wear out is how often you fly the aircraft. It sounds logical to assume that an active aircraft will wear out before an inactive one. For some components that is correct, but for others it's not. Aircraft activity wears out those items that are constantly in motion and/or under stress in flight. Inactivity means components can rust, corrode, and dry out.

To complicate things, "active" is a relative term. One person might say an active airplane is one that flies at least 200 hours a year. Another puts the minimum at 50 hours a year. A third might say at least once a month. Regardless how you define active, the key to achieving normal wear is to exercise the aircraft on a regular schedule.

Let's look at how frequent operation versus prolonged inactivity affects one of the most critical and expensive aircraft components - the engine.

An engine accumulates wear through normal use just as any mechanical device does. Normal wear means gradually increasing clearances between the engine's moving parts, with the associated loss of compression, performance, and reliability due to stress and heat over time.

Engine manufacturers have established recommended times between overhaul (TBO) as a guide to give owners a realistic idea of reliable engine life, and some ability to plan for engine overhaul logistics and expenses when the time arrives.

An aircraft owner should be aware that the engine also undergoes wear if the aircraft is seldom-used. This might come as a surprise to some, but it's true and logical. A seldom used engine will corrode and rust internally, which creates a rougher surface between mating parts. The engine will also be poorly lubricated at first because the oil has drained away from internal engine parts during its extended inactivity.

When you finally start an engine that has not been operated for a long period, two things will probably happen. First, you will have to use more power to overcome the lack of lubrication, so initial rpm will be high. Second, internal friction and wear will be much greater during that initial startup. Internal corrosion, higher rpm, and dry parts cause the extra wear, which can easily be as great or greater than that of a frequently run engine. Prolonged inactivity affects a variable pitch prop and engine accessory components, such as prop governors, in much the same way it affects the engine.

Prolonged inactivity is especially hard on camshafts and valve lifter bodies in engines where the camshafts are above the crankshaft. Camshafts are under great pressure from the lifter bodies, and high-rpm dry starts will quickly produce significant cam and lifter body wear. At least one engine manufacturer recommends an oil additive to retain lubrication on the cam and lifter bodies to help reduce this significant wear.

If your aircraft must sit for a long period, use the manufacturer's recommended oil additive to help protect the cam and lifters. Remove the top spark plugs (the owner/operator can do this), squirt some engine oil onto the cylinder walls, pull the prop slowly through several revolutions by hand to spread the oil over the cylinder walls, and replace the plugs with moisture-absorbent storage plugs. Do not move the prop again until you're ready to reinstall the spark plugs and start the engine.

Inactivity affects aircraft brakes, too. Brake discs (or drums) will rust, and this literally grinds away the brake pucks or linings during the first few brake applications after an extended rest. You can't do much to prevent it, either. Don't attempt to use any type of rust inhibiting agent on the brake discs or drums because it may reduce braking friction and effectiveness to a dangerous level. The only real prevention is to fly your airplane often.

Inactivity also adversely affects aircraft batteries. When you recharge a battery after it has lost a significant amount of charge, it loses some of its useful life, even though it takes a charge and works fine for awhile. Also, a low battery can freeze in cold weather. If an aircraft is to be stored or is inactive, remove the battery, keep it someplace warm, and keep it charged.

Inactivity is hard on components such as bearings, tires, seals, hoses, gaskets, and fuel systems, too.

Active aircraft will wear whenever aircraft parts are in motion, wherever vibration causes stress, whenever you remove or replace parts, and wherever it comes in contact with the relative wind. These areas include fuel and oil cap seals, oil and other preflight inspection access panels, bearings, push-pull controls, pedals, control yoke and control stick assemblies, flight controls, pulleys, cables, cowlings, fairings, airfoil leading edges, and fasteners that are operated routinely.

Aircraft interiors definitely wear from regular use. The plastic panels in most of today's aircraft are particularly susceptible to cracking and breaking. Door panels crack easily and you can damage them by pushing and holding them open with your feet. If you park your aircraft outside, use sun-blocking panels inside the windshield to prevent UV radiation and heat from fading and damaging interior fabrics and plastic components.

Exterior plastic or fiberglass components, such as wing tips and fairings, are a continuing irritation and expense. Exposure to the sun weakens them over time, and vibration or minor impacts cracks them. Unless you're luckier than most, you'll either replace the exterior plastic trim pieces on your aircraft often, or you'll learn to live with them being in less-than-perfect condition.

Avionics are susceptible to wear from a number of sources. Moisture is a critical factor in the operation and life expectancy of anything electrical or electronic. As an aircraft ages, leaks around the windshield, especially while the aircraft is parked, can be a problem. An undetected or uncorrected leak that lets moisture enter the avionics rack will quickly destroy the radios when you turn on the avionics master switch. Excessive heat that builds in a closed aircraft parked in direct sunlight can also adversely affect the life expectancy and reliability of your avionics.

The buyer of a brand new aircraft has two additional things to think about. When I was a ferry pilot for several general aviation manufacturers, I routinely found loose and even missing panels, improperly adjusted cables and flight and engine controls, improperly fitting pieces, nonfunctional avionics, inoperative heaters, inoperative lights, and other malfunctions and missing items that should have been checked at the factory. The buyer of a new aircraft should be alert for items such as these.

The buyer of a brand new aircraft must also watch out for components that fail prematurely. If a mechanical device is going to fail, it will either happen early in its expected life span or remain functional for its projected life - or something close to it. New aircraft often have component failures in the first 50 to 100 hours. If a component makes it past that point, it's likely to be reliable for at least close to its projected life.

If you give your aircraft proper routine care and attention, operate it responsibly, and give it some additional care if it is to be inactive for an extended period, it will last for many hours of enjoyable flying.