Just because a plane is 30 years old doesn't mean it's not fit to fly. What matters is condition, not age.
Aviation experts say the US has one of the most rigorous, disciplined maintenance programs in the world, one that allows planes to fly for decades. In fact, the jet that ferried JFK and Lyndon Johnson around the world is still in service, now flying private corporate clients.
But week-long hearings into cause of the explosion of TWA Flight 800, which are scheduled to wrap up today, have revealed serious weaknesses in those maintenance systems, particularly with aging aircraft. Now, the National Transportation Safety Board (NTSB) wants the Federal Aviation Administration (FAA) to overhaul its requirements for older planes.
"The FAA's program for aging aircraft now looks at structure - rivets and grommets," says Shelly Hazle of the NTSB. "We think they should also be looking at the planes' operating systems."
Investigators now suspect corrosion and damaged wiring on the 25-year-old plane may have caused the spark that ignited the explosion in Flight 800's center fuel tank on July 17, 1996. All 230 passengers were killed.
The NTSB also found that temperatures in a similar 747 fuel tank rose to a volatile 125 degrees F. when subjected to the same conditions as Flight 800's. Boeing Co. has now said it may have to redesign its planes' fuel systems to prevent combustible fumes from building up.
Another surprise was the potentially deadly nature of small, corrosive deposits found on some wires and fuel probes. One of several theories postulates that a short circuit combined with the corrosion on a probe inside the tank sparked the blast. Therein lies one of the blind spots in the maintenance programs.
"It's a constant battle to understand what happens to an airplane as it gets older," says Richard Golaszewski, executive vice president of GRA Inc., a transportation consulting firm near Philadelphia. "The premise is that you can develop an inspection and overhaul program to operate those planes safely."
The FAA currently requires planes go through routine, rigorous inspections. At TWA, mechanics check the most basic operating systems at least every other day. At every 100, 800, and 1,200 hours of flight time, increasingly more detailed inspections and maintenance are done. Once a year, the plane is taken out of service for a week for a comprehensive overhaul. The process culminates with what's called the "D" Check. At least once every four years, the plane is essentially taken apart and scoured from nose to tail.
That is the only time the center fuel tank is inspected. Wiring is usually left intact, unless inspectors see a problem that needs to be corrected. Fuel probes and pumps are also left alone, unless there's a problem.
In 1983, Boeing started an "aging aircraft program" to give special attention to planes that have exceeded their "operational design life," usually about 20 years, or 20,000 takeoffs and landings, known as cycles.
The FAA also instituted its own set of guidelines and requirements for older planes after the 1988 Aloha Airlines accident, in which part of the fuselage ripped off midair.
But the focus of both efforts is on a plane's structure.
"The initial major concern was over fatigue cracking," says Robert Vannoy, Boeing's chief of 747 support. By contrast, when systems such as fuel-indication and navigational devices fail, flight and maintenance crews are usually alerted immediately, he argues. For instance, a fuel gauge may register erratically or the lights will flicker if there's an electrical short. The problem is fixed immediately.
Mr. Vannoy contends that with proper service, planes have no age limit. Of the 1,140 747s built during the past 28 years, 340 have exceeded their operational life spans. Most are still in service.
Flight 800 had flown 18,000 cycles. According the NTSB's investigative docket, none of the 65 fuel probes or 13 fuel compensators in Flight 800 had been replaced during the plane's lifetime. "I want to stress that we still don't know what caused the accident," says the NTSB's James Hall. "But we are interested in learning whatever safety lessons we can."
The FAA says it will overhaul its aging-aircraft program to include all systems, even the wiring. "What this does is just put more light on an issue that is not new," says Eliot Brenner, assistant administrator of the FAA.