Tags: Boeing | Suspect | Jetliner | Crash

Boeing Suspect in Jetliner Crash

Monday, 20 November 2000 12:00 AM

According to Sunday report in the Seattle Times:

It could mean that Boeing would be required by the Federal Aviation Administration to redesign a critical part of the tail assembly and retrofit it on all 2,000 of its DC-9/MD-80s worldwide.

National Transportation Safety Board investigators now suspect that part broke off while Alaska Airlines Flight 261 was in flight from Puerto Vallarta, Mexico, bound for San Francisco and then Seattle, making it impossible for the jet airliner to pull out of its sudden, fatal dive into the water just north of Los Angeles.

Based on information analyzed from the doomed plane's flight-data recorder and parts of the tail assembly recovered off the ocean bottom, an NTSB investigator has concluded the only way Flight 261 could have nosed over into such an acute dive was if a part called the end stop – a fail-safe device to keep the horizontal stabilizer intact – broke off in flight.

That is directly at odds with the manufacturer's analysis that the end stop broke off when the plane struck the water, not as it flew.

Until now, suspicion had focused on Alaska Airlines for its maintenance of a mechanism called the jackscrew that adjusts the up or down pitch of the stabilizer, the wing-like structure on the tail that helps the plane fly level, descend or climb.

Investigators have been looking into whether the jackscrew on this particular flight should have been replaced three years before the crash. An Alaska Airlines mechanic's order to replace the part in September 1997 was rescinded several days later by other mechanics.

The function of the end stop is to keep the stabilizer's leading edge from tilting up more than 2.2 degrees, the angle designed to produce the maximum downward thrust of the nose.

But the NTSB now believes the stabilizer may have swung up 22 degrees – 10 times the normal maximum, which could have happened if the end stop had broken off in flight.

Its latest theory could result in responsibility shared by the manufacturer and the airline maintenance:

There were two dives, the first down to 24,300 feet from 31,000, possibly caused by a failure of the jackscrew, and the second, more severe dive, into the ocean from 18,000 feet, due perhaps to the end stop breaking off during the initial plunge.

The two experienced airline pilots had managed to level off Flight 261 after it first dived 7,000 feet in one minute.

Nine minutes later, from an altitude of more than three miles, something caused the plane to pitch down into its final, more dramatic dive – descending 26 degrees per second for several seconds and sending the 80-ton jetliner on into the ocean.

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According to Sunday report in the Seattle Times: It could mean that Boeing would be required by the Federal Aviation Administration to redesign a critical part of the tail assembly and retrofit it on all 2,000 of its DC-9/MD-80s worldwide. National Transportation Safety...
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2000-00-20
Monday, 20 November 2000 12:00 AM
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