Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: SUNDAY, April 11, 1993 TAG: 9304110047
SECTION: NATIONAL/INTERNATIONAL PAGE: A-6 EDITION: METRO
SOURCE: The Washington Post
DATELINE: LENGTH: Medium
COMPUTER TESTS OFFER CLUES IN 747 CRASHES
The Federal Aviation Administration says Boeing Co. has made a computer-assisted metallurgical discovery that may help explain why engines sheared off of two Boeing 747 cargo jets, including one that crashed into a crowded apartment complex in Amsterdam last year.Boeing simulations on a Cray supercomputer found that fuse pins, which hold the engines to the wing, react under load in an unexpected way that can produce stress within the pin eight to 10 times greater than engineers had anticipated, according to Anthony J. Broderick, FAA associate administrator for regulation and certification.
The greater-than-expected stress causes any corrosion-related crack in the pin to grow faster than engineers had thought. The result is that older pins weaken more quickly.
Broderick and a spokesman for the National Transportation Safety Board (NTSB) stressed that fuse pins on the more than 900 747s in service are adequate. Uncracked, uncorroded pins are strong enough to support the engine properly, and older pins already are under strict inspection requirements. The FAA, NTSB and Boeing said the 747s are safe to fly.
Failed fuse pins are one possible cause of the crash of a China Airlines 747 on Taiwan on Dec. 21, 1991, and an El Al 747 in Amsterdam on Oct. 4, 1992. In each case, both engines ripped away from one wing as the jets were climbing after takeoff. The El Al jet crashed into an apartment complex housing many undocumented foreign workers, killing more than 50. On March 31, an engine tore off a 747 cargo jet at Anchorage, but an investigation has determined that fuse pins were not a factor.
The 747, first flown in 1968, is the world's most popular jumbo jet.
Each of the 747's four engines has four fuse pins designed to break free in a crash landing or in a catastrophic engine failure that otherwise might rip a wing from the fuselage. There is no indication of such an engine failure in either the Taiwan or Amsterdam crash.
Broderick said in an interview that the new tests provide a "credible, reasonable explanation why the midspar fuse pins on two aircraft broke." The midspar pins, each about the size and shape of a soft-drink can, are the two in the middle of the wing.
Corrosion and cracks have been a chronic problem on older fuse pins, although the cause had been a mystery.
Broderick, whose office is responsible for certifying airplanes and parts as safe to fly, said that without the Cray supercomputer it would have been impossible to determine "the peculiar behavior of this particular kind of pin."
Even with the super-fast computer, each simulation takes 13 hours.
Keywords:
FATALITY