Safety Pilot: What makes an aircraft old

December 1, 2007

Bruce Landsberg is the executive director of the AOPA Air Safety Foundation.

News flash: a generation of aircraft is getting older. The thousands of shiny new machines that were built a human generation ago are now senior citizens. These "boomer" aircraft were built in what many call the golden era of general aviation. In the late 1970s and early 1980s, thousands of new aircraft were added to the inventory, and they make up a large number of active aircraft. Although nothing lasts forever, well-maintained light aircraft will outlive most vehicles. The operative term is "well-maintained." How do we know when our aircraft is getting old? What are the symptoms, and do aircraft become less safe as time goes by? How can we best manage the risk?

The AOPA Air Safety Foundation has just added a new online course, Aging Aircraft, to its course catalog. Whether your aircraft is new, a boomer, or older, or if you're thinking about buying an older machine or just renting one, it's a good idea to understand the nature of the potential problems. This course will help you to do just that. As with people, aircraft age is far more than just a number. How aircraft are used, how they are built, and how they are stored all have a bearing on geriatric status.

ASF has been watching the statistics for more than a decade as they relate to accidents that were caused by mechanical failure according to the NTSB. Mechanically related accidents have averaged about 16 percent during the past five years for which we have data. Most of these appear not to be related to age per se. Deferred maintenance and, rarely, a bad repair job are the primary causes. The data are difficult to parse to get a true picture of when a tired part failed, but there is one axiom that is true of all machines. As they age, aircraft will require more maintenance, and ignoring your manufacturer's, mechanic's, and type club's recommendations is not a good long-term strategy. The course addresses problem areas in the most popular models.

Recommendations

Basic design is less important than usage and storage, but it can be a factor. Here are some obvious, if regularly ignored, recommendations. Sun and water take a heavy toll on anything left outside. Compare two cars of the same vintage, one parked outside and one residing in a garage. You'll be able to tell immediately which is which. Sun fades aircraft paint, and the paint will eventually deteriorate. Ditto on upholstery and plastics in the cabin. Some pilots rationalize that five years of hangar rent could just as easily be put toward a new paint job every five years. That's true, but consider the windshield, side windows, and interior wear. The real price just got steeper, not to mention the depreciation or resale value. These are economic concerns, not safety problems.

Although paint is largely cosmetic, it does protect the skin. Windows, however, have a direct safety impact when they craze and haze, as other aircraft become harder to see. Rainwater is a bigger deal because it will eventually get into the airframe when the aircraft is parked outside. If you park anywhere near the ocean, rainwater and the humidity will distribute that tremendously corrosive and pervasive substance—salt—into nooks and crannies. Our three biggest aviation states—Florida, Texas, and California— have lots of saltwater coastline, as does New England. The aircraft population in these areas is extensive, and so is the potential for damage. Some aircraft have been treated with zinc chromate primer or aftermarket treatments, which will delay but probably won't stop corrosion completely.

There have been very few fatal accidents involving undetected corrosion that led to structural failure. The most notable recently was a Grumman amphibian used in commercial service between Florida and the Bahamas that crashed in December 2005. That's an admittedly extreme case, but it shows what can happen without proper vigilance.

Some aircraft leak more than others, and saturated sidewall insulation may affect control cables and wiring. Cable attach points and brackets corrode. It's hard to believe that stainless steel can rust or wear out, but it happens. Wire insulation and bundles also deteriorate. That leads to equipment failure or possible short circuits. Much of this wear occurs in areas that may not get regular inspections. Depending upon how the aircraft was built it may be necessary to remove the interior, the headliner, or the floorboards to get a good look at some of these problem spots. It's time consuming and expensive but essential on a pre-purchase inspection.

Hours in the air

How about airframe hours as a measure of age? Fewer are generally better, but—and this is a big caveat—a moderately high-time, one-owner cross-country aircraft may be in much better shape than a lower-time flight-school aircraft. As in automobiles, highway miles—or cross-country hours in this case—are much less wearing than the rigors of half a dozen takeoffs and landings every hour. In larger aircraft, a takeoff and landing (or a cycle) is one of the primary measures of when heavy maintenance is needed.

Pressurization demands some consideration. These systems are extremely reliable, but when they fail they can do so catastrophically. In 1988 an old Aloha Airlines Boeing 737 had the roof peel back like a sardine can in flight, and that started the FAA on a major quest to look for fatigue signatures before a failure. To my knowledge, there has not been an accident because of pressure vessel fatigue failure on a piston aircraft such as the Cessna P210 or the Piper Malibu, but the FAA does require periodic testing. Our aircraft are well engineered in this area.

The big maintenance item is the engine and its accessories. Failures can be catastrophic, and preventive maintenance is essential. Here is where the age in hours can be quite deceptive. Low hourly time but high calendar time often means internal corrosion. It may not result in a disaster, but the engine isn't likely to produce the horsepower on which all the performance figures are based. Betting your life on a short-field takeoff in a heavily loaded aircraft with a weak engine...well, you get the idea.

Exhaust systems are another critical area where everything has to work properly lest there be a fire or carbon monoxide mishap. Turbocharging doubles not only your usable altitudes but often the maintenance cost. Twin Cessnas have been on the FAA's watch list in this area, and ongoing inspections are required to ensure the integrity of the systems. This is not an area to skimp.

Fuel systems—including tanks, bladders, sealants, seals, and O-rings—are the source of several accidents annually. The usual scenario is that the aircraft hasn't flown for a while, and there may be contaminants in the fuel such as water or other life forms not known to man. The pilot does a quick sump, maybe a quick runup, and gets airborne only to have the engine develop severe indigestion in the most critical place. If the aircraft has been parked for several months, especially outside, it's not a bad idea to have a technician give it a checkup to prevent nasty surprises.

Wing spars and attach points occasionally cause problems, especially if the aircraft is used in high-stress activities. Fatigue accidents have occurred in pipeline patrol aircraft that hump and bump through thousands of hours of low-altitude thermals. Older aircraft used in aerobatic or mock combat maneuvering have had spar failures that make a conservative maintenance approach a good idea. With proper maintenance and adhering to flight limitations, such as not overstressing, these machines can last a very long time. If you are going to rent or fly in one of these aircraft, a few maintenance-related questions are a good idea.

To see and learn more about aging aircraft as a potential buyer or renter, visit the Web site and see the online course area.

The AOPA Air Safety Foundation is indebted to the American Bonanza Society, the Cessna Owner Organization, the Mooney Aircraft Pilots Association, Mooney Owners of America, Cardinal Flyers Online, the Piper Owner Society, the FAA's Small Airplane Directorate, and Dennis Wolter of Air Mod for providing much technical expertise in identifying areas of special attention in various models of aging aircraft.