Grease used on jackscrew examined in crash probe settk-oa

Posted: Friday, August 18, 2000

SEATTLE (AP) -- Grease used on the jackscrew assemblies for the horizontal stabilizer on Alaska Airlines MD-80-series jets is being examined in the investigation into the crash of Flight 261.

The purpose is to determine whether two types of grease might be incompatible, leading to a buildup of grit and faster wear, and whether one type could cause corrosion in a gimbal nut, said Terry Williams, a spokesman for the National Transportation Safety Board.

A report on the tests was published Friday by The Seattle Times.

Williams said the agency began testing after learning the airline had made tests without notifying federal investigators, which he described as a breach of protocol.

The jackscrew is a key part of the investigation into the crash of an Alaska Airlines MD83 into the Pacific Ocean off Southern California on Jan. 31. All 88 people aboard died.

The screw is used to operate the horizontal stabilizer, a wing-like structure on the tail that is used by the pilot to direct the nose of the plane up or down.

Alaska Airlines tests indicated that AeroShell 33, which the company began using in 1997, might cause problems if it came in contact with the previously used Mobilgrease 28, sources who asked not to be identified told the Times.

Those sources indicated the combination resulted in formation of a pasty substance that would attract dirt and foreign material, possibly increasing wear and tear on the jackscrew.

Another possibility was that AeroShell 33 might cause corrosion in copper.

The jackscrew, a 2-foot-long, 1 1/2-inch-diameter threaded shaft of hardened steel, moves up and down through a stationary gimbal nut to adjust the stabilizer. The gimbal nut is made of bronze, an alloy of copper and tin.

Threads in the gimbal nut from Flight 261 were found stripped and twisted around its jackscrew. There was some grease on the jackscrew but none on that part that normally was in contact with the nut.

Williams confirmed that the safety board is testing for incompatibility of the two greases and the corrosion potential of Aeroshell 33.

''Further, the composition of the remnants of grease found on the jackscrew and gimbal nut is being studied,'' Williams said. ''We do not know the import of any of this -- including any wider safety issues -- yet.''

As for company testing, board chairman James Hall ''has spoken to (Alaska Airlines) CEO John Kelly and president William S. Ayer to express his displeasure with what occurred,'' Williams said.

In exchange for participation by experts from airlines, airframe and engine makers, suppliers and labor unions in investigations of airline disasters, each potentially culpable party agrees to take direction from the board's investigator-in-charge and to divulge everything relevant to the probe, he added.

Alaska Airlines has ''cooperated fully with the NTSB investigation,'' spokesman Jack Evans said.

''If there are concerns about any of our actions, we'll gladly discuss those with the NTSB and any of the parties to the investigation,'' Evans said, ''but we won't do so in the media.''

Alaska Airlines, the dominant carrier on north-south routes along the West Coast, operates about 500 flights a day with a fleet of 90 planes, including 34 MD-80s.

Evans would not say why the company switched to AeroShell 33.

John Thom, a Boeing Co. spokesman, said the manufacturer was asked by Alaska Airlines about the two greases in 1997 and responded in writing that Boeing had ''no technical objection'' to the switch.

Williams said Alaska Airlines has switched back to Mobilgrease 28.

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