Aging Aircraft, Part 2

The average age of the U.S. general aviation fleet is already past 30 years, according to the Federal Aviation Administration (FAA). Despite new-plane manufacturing, this average continues to keep pace with the march of time — FAA forecasts for the year 2020 show the typical single-engine, piston-powered airplane will be nearly 50 years old. The simple truth is that the rules under which virtually all of these airplanes were certified — the old Civil Aviation Regulations Part 3 — had no standards for use- and age-related fatigue or continued airworthiness. No one really knows what the ravages of time will do to airplanes.

To head off the effects of aging, the FAA gathered government, industry and airplane owners to develop a program described in its Best Practices Guide for Maintaining Aging General Aviation Airplanes (External Adobe .PDF). Last week we looked at the genesis of this Guide, and the first of its two recommendations — airplane records research. This time we’ll look at the second recommendation, the call for special attention inspections.

An airplane spends far more time on the ground than in the air. Therefore, the environment it is exposed to while on the ground plays a significant factor in how it ages. Ask yourself:

  • Has the airplane been stored outdoors? An airplane stored outside will have additional wear on hoses, seals, fuel tank bladders and windows when compared to those on a hangared aircraft. The likelihood of structural corrosion is increased. Fiberglass and plastic parts can become brittle. Damage from long-term exposure to bird and bat nests and droppings, and vent line blockage from insects, is more likely outdoors than inside. The weight of heavy snows won’t likely affect wing and horizontal stabilizer spars but may affect control surface rigging or hinges; strong winds may have buffeted the airframe and controls.
  • Has the airplane been stored in a hangar? Generally a hangared airplane is less likely to have environmental damage. But airplanes stored inside are more often infested with mice … and the corrosive results of their nests and droppings. Mice also like to chew electrical insulation, so airplanes hangared for long periods without active rodent control may have severe electrical problems.
  • Where, geographically, has the airplane spent most of its time? Climate plays a major role in the longevity of an airframe. Airplanes stored (inside or out) in coastal climes are much more likely to have significant corrosion — Florida seems especially harsh on airplanes. Extremes of heat or cold take their toll on certain electrical equipment, wiring, and plastic, fiberglass, composite and Plexiglass™ parts. Light airplanes built before the 1990s (that is, almost all light airplanes) were usually kept light in part by avoiding the use of corrosion protection and undercoatings.

The airplane’s frequency and manner of use also plays a vital role in how well it resists age. Consider:

  • Has the airplane been active? Although wear-limited parts “age” more rapidly with more frequent use, it seems inactivity is far harder on most aircraft structures and components. A plane that flies less than about once every week or two may have corrosion issues as moisture is given time to work into metals, or especially wood parts. Lubricants drain down off metal parts when the airplane sits for long periods, exposing those parts to corrosive air and allowing seals, hoses and bladders to dry and break. An engine may show several hundred hours before the next Time Before Overhaul (TBO) but never make it close if the time in years since the last overhaul is excessive.
  • How has the airplane been used? Airplanes in low-altitude patrol, aerial survey or photography roles often have fatigue issues far advanced for their calendar age. Aircraft used for banner towing or flight instruction are also subjected to additional stresses that may register against the airframe. Mountain flying or charter use (where airplanes are more frequently flown at high operating weights), aerobatic airplanes, or those with an abnormally high number of takeoffs and landings (parachute “jump planes“, and again, instructional use) are exposed to more fatigue-inducing stress than a personal airplane of the same vintage.

Knowing something about the airplane’s storage, location and use history will tell you whether your particular airplane is more or less likely to suffer the dangerous effects of aging.

The airplane records check and knowledge of the individual airplane’s history will only point out the possibility that the airplane may suffer from the ill effects of age. The only way you’ll know for certain is to conduct a detailed, focused inspection of the aircraft. The FAA’s Aging Aircraft team calls this a special attention inspection, the “special attention” being directed toward those items which experience is beginning to show may be more likely to be affected over time. Bear in mind this the special attention inspection is not an “annual inspection,” nor does it follow the annual inspection checklist recommended by most airframe manufacturers … although the special attention items of course may be performed as a part of a scheduled annual inspection.

The FAA’s Best Practices Guide contains an appendix listing items for a generic special attention inspection. Items on this checklist meriting a closer look include:

  • General condition checks
  • Avionics
  • Controls and trim
  • Electrical system
  • Empennage (a common area for overstress fatigue)
  • Engine
  • Fuel system
  • Fuselage
  • Instruments
  • Landing gear
  • Modifications
  • Propeller
  • Repairs
  • Other systems
  • Wing structure

Each topic area is further broken down into subtopics — for instance the “fuselage” check includes scrutiny of seat tracks, attachments of wings, landing gear and tail, and removal of all interior items, side panels carpeting, and access panels to inspect for corrosion or cracks. The FAA even recommends that owners consider adding access panels (with proper Federal approval) to better keep an eye on hard-to-inspect parts of the airplane.

The Guide encourages owners of older airplanes (by FAA definition, “aging” means “more than 30 years old“) to conduct an initial special attention inspection, noting the current condition of all aircraft parts and recording those conditions and the date of the check. They should tailor the inspection to the airplane type, its storage, location and use history, and any “items of interest” that result from the aircraft records search. More intrusive inspections, like borescope, dye penetrant, magnetic particle, ultrasound and eddy current checks, may be necessary in some airplane types, or to track certain types of problems. Most special attention inspection checklist items should be added to the owner’s personal annual inspection checklist. More intrusive checks should be done once every five to 10 years, according to the Guide, more often if you have reason to suspect problems. Owners must strive to strike a balance between early detection of age-related trouble, and the possibility that the inspection itself may cause or accelerate the progress of damage.

The Feds don’t expect airplane owners to do this alone. That’s why the FAA’s Aging Aircraft Summit meetings include representatives from airplane owner’s groups, and especially airplane “type clubs,” so named because they exist to support the operation and maintenance of a particular “type” of airplane. Type clubs are already part of the process by which the FAA considers and issues Airworthiness Directives (ADs), often the result of airplane aging issues. The Globe Swift Foundation and the American Bonanza Society are founding members of the FAA’s Aging Aircraft Summit group.

The Best Practices Guide encourages airplane owners to join the type club appropriate to keeping their airplane flying. Further, it expects the type clubs to provide their members an inspection supplement to the Best Practices Guide highlighting the specific aging-aircraft issues that apply to their members’ airplanes. To find a type club for your airplane’s make and model, try an internet search by your airplane type’s designation, look in magazines or ask around the airport, or contact the Aircraft Owners and Pilots Association (1-800-872-2672, or the Experimental Aircraft Association (1-800-843-3612,

BOTTOM LINE: Like all of us, airplanes aren’t getting any younger. No one knows what “medical conditions” may befall them as they age. So like with aging pilots, its best we take an occasional, close look at aging airplanes to head off any potentially disastrous conditions. The FAA, industry and airplane type clubs have given us a means of keeping our aging airplanes in the air.