SUMMARY OF HEARING: Thursday, December 11, 1997

The condition of aging aircraft was addressed in the fourth day of the NTSB public hearing into the explosion of TWA flight 800, with experts from the NTSB, Boeing, TWA, the U.S. Air Force and the FAA taking up the issue of how old aircraft might deteriorate and what new maintenance they might need.

The TWA Boeing 747 that went down was 25 years old. It had 18,000 flight cycles and 90,000 hours. Boeing’s chief of 747 fleet support, Robert Vannoy, said 747s were built with a design life of 20 years, 20,000 flight cycles and 60,000 hours. He said Boeing and the industry had a program for aging planes, as does the FAA, studying them and recommending new maintenance programs for them.

But Robert Swaim, an NTSB aircraft systems investigator, said that most aging aircraft programs concentrate on the structure of metal skin and internal framework and not on electrical, fuel and other systems.

In the case of flight 800, the NTSB has found that the plane’s center wing fuel tank exploded, but investigators have not yet determined the cause of the explosion. Among the possible ignition sources being investigated are aging wiring inside the fuel tank and wiring leading to it.

NOTE: The NTSB began a final panel discussion on fuel flammability reduction late Thursday and will conclude it on Friday, when the public hearing is to end.