Alaska Airlines Crash

Posted: Monday, November 20, 2000

SEATTLE (AP) -- A federal investigator says there is only one explanation for the deadly crash of Alaska Airlines Flight 261 in January: A piece of the plane's tail-control mechanism broke off in flight, keeping pilots from pulling the jet out of its sudden dive into the Pacific.

Eighty-eight people were killed when the Boeing MD-80, en route from Puerto Vallarta, Mexico, to San Francisco and then Seattle, crashed Jan. 31.

The National Transportation Safety Board is still investigating the cause of the crash and has public hearings scheduled next month in Washington, D.C., to discuss the investigation's progress.

According to The Seattle Times, NTSB performance analyst Dan Bowers has analyzed information from the jet's flight-data recorder and concluded the only explanation for the plane's steep dive is that the end stop, a piece of the jackscrew assembly, broke off in flight.

The end stop is part of the flight-control mechanism designed to keep the plane's horizontal stabilizer intact. The horizontal stabilizer is the winglike structure on the tail that helps the plane fly level, climb and descend.

Bowers programmed a flight simulator to mirror Flight 261's moment-to-moment position changes during its fatal dive. The only way Bowers could re-create the final part of the dive was by tilting the stabilizer up 22 degrees, The Times said.

The end stop, attached to the bottom of the jackscrew, prevents the stabilizer from tilting up more than 2.2 degrees -- the angle at which the stabilizer is designed to produce its maximum downward force on the nose.

The only way to reach 22 degrees is to separate the jackscrew from the end stop, the newspaper said.

If the end stop is found to have broken in flight, rather than on impact, some liability for the crash could shift to Boeing, the newspaper said.

Such a finding also would raise more questions about the design of the part, which is in use on the more than 2,000 MD-80 and DC-9 jets in service worldwide.

''Everyone agrees that it did break off but we don't know where'' or when, Boeing spokeswoman Liz Verdier said Sunday. She said the aerospace giant had turned over all test results and data in the case to the NTSB. ''We have drawn no conclusions,'' she said.

Alaska Airlines' Terry Clark, who is coordinating the airline's participation in the NTSB investigation, called for a retest by independent experts.

''I can only assume that the apparent irregularities in assembling the test ... were an innocent error because the effect on the test results would be substantial,'' Clark said, according to The Times.

To win certification of the DC-9/MD-80 stabilizer system in the 1960s, McDonnell Douglas designers -- the company has since been acquired by Boeing -- had to provide the Federal Aviation Administration with analyses showing that the odds of the end stop failing were one in a billion.

Investigators also are looking into whether the plane's jackscrew assembly was so worn that it should have been replaced three years before the crash. An Alaska mechanic had ordered it replaced in September 1997, but other mechanics overruled him several days later.


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