If Only Cars Were Maintained Like Planes

May 17, 2006 — -- The corollary to the phrase "if it ain't broke, don't fix it" arises from a very old principle that a machine needs maintenance only when it no longer works. But if we ran commercial aviation that way, the ground would be littered with broken air machines, and no one in his or her right mind would risk flying anywhere.

There was a time, of course, when aviation did follow that "wait for it to break" rule. In the 1920s and '30s, when flying was still somewhere between a circus act and a daredevil routine (and airlines were just beginning), what's now called preventive maintenance consisted mostly of experienced pilots trying to head off catastrophic in-flight failures by changing spark plugs and control cables before they could go bad.

Formal, federally mandated programs for anticipating when something might break and replacing it (or overhauling it) before it failed were still decades away, although World War II accelerated the process immeasurably. Among other innovations, contract military flight training schools learned to fly their airplanes by day and maintain them by night in a continual cycle, removing items that were considered ripe for failure when the mechanics decided it was time.

In the '50s, however, the advent of extremely complex turbo-compound piston engines powering such large airliners as DC-7s and Lockheed Constellations meant that an entirely new method of dealing with aircraft maintenance had to be formalized, since waiting for a turbo-compound engine to break usually meant massive expense and trouble.

So about the time the Federal Aviation Administration was born in 1956, the major airlines instituted their own formal, structured programs to maintain their hardware in a way that would prevent in-flight failures by using hard and fast removal and replacement rules.

In other words, if a particular hydraulic pump could be expected to run trouble-free for 2,000 hours, and replacing it automatically at 1,500 hours of service would reduce in-flight failures to a very small number, the formal requirement would be written to replace that pump every 1,500 hours. The result of applying this new philosophy across the board -- engines, airframes, subsystems and electronics -- created a dramatic improvement in the overall mechanical reliability of air travel.