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.

In addition to timely replacement, another major change made about the same time can still be witnessed every time you glance into an airliner cockpit and see more than one pilot there. The idea was that no single failure of any critical airplane component should ever be allowed to leave an aircraft unflyable. Thus, carrying a backup pilot, and carrying two or more backup engines along with backup hydraulic and electrical systems, gave us a step-by-step method of preventing accidents that might otherwise occur from any single mechanical failure.

By the time the jets entered commercial service in the form of Boeing 707s, Douglas DC-8s and Convair 880s in the early '60s, this philosophy was entrenched and proved, although with a twist: Even when there were four engine-driven electrical generators, for instance, where only one was needed for flight, we learned that flying with less than all four increased the possibility of an accident.

In other words, the backups became an integral part of both the basic safety equipment of the aircraft and the philosophy of operation, and that is reflected today in the fact that the loss of one engine on a four-engine airplane today is still considered an emergency requiring an immediate landing at the nearest suitable airfield.

We no longer build flight safety on having just one operable engine, in other words, we build it on always having those backups backing up the backups. The result has been another significant reduction in accidents worldwide.

Pound of Prevention

Of course, to basic nonaviation companies such as a manufacturer needing to keep a production line going, that may seem strange. Why not accept the loss of one of four generators and keep on producing, replacing that dead generator only when it's convenient and you've shut the line down for other reasons? Well, too often in the financially stressed 1980s, airlines did exactly that, pushing the FAA rules to allow multiple flights to take off even with certain equipment inoperative, even though it meant fewer backups in an emergency to absorb new failures.

In the last days of Eastern Airlines, for instance, it was not unusual to climb into a cockpit jumpseat as a guest airline pilot and see orange Minimum Equipment List "inop" stickers all over the panels, sometimes numbering in the 20s, and each representing an inoperative component the FAA allowed them to fly with for a while (a heart-stopping circumstance the passengers never saw).

In the 1990s, however, when financial times improved for the airlines that remained, many of those practices went away with stronger rules against multiple inoperative components. Today the understanding is even more widespread that if you permit continual flight with less than a full complement of the backup equipment on which aviation safety is based, you'll be edging back toward the point where one or two failures could cause a tragedy.

Preventive maintenance, therefore, is more than just replacing or overhauling things before they have a chance to break. It's a philosophy that holds that we can know the way all mechanical as well as human components of a system can fail, and by servicing them before those failures occur, we can prevent 98 percent of the emergencies that aircrews would otherwise have to respond to in flight.

Cars, on the other hand (and most trucks), are still maintained the old-fashioned way: When they break, they're fixed. The argument against incorporating more expensive preventive maintenance techniques to anything rolling down a road is that one can always pull over to the shoulder in a car or truck. But when you look at the overall costs of having a car or commercial truck out of service, as well as the costs of dealing with the breakdowns themselves -- and the often serious damage done by a failing component -- preventive maintenance for vehicles looks a lot more attractive.

Indeed, the very act of lubricating a car and doing certain manufacturer-recommended inspections is a form of preventive maintenance, but we need much more of it. And, in fact, the same principles work very well in a wide variety of business and personal pursuits not only with respect to preventing mechanical things from breaking at the wrong time but preventing people from breaking as well, by being professionally aware of where our breaking points really are.

Today, when you climb aboard any airliner in the U.S., you can have serene confidence that just about any potential problem that a failing component might throw at your aircrew has been greatly minimized by the airline's preventive maintenance procedures, and the fact that flying multiple trips with any significant backup components inoperative is seldom, if ever, done.