More damage discovered on part from Alaska Airlines Flight 261

The jackscrew from Alaska Airlines Flight 261, left, and the gimbal nut

February 18, 2000
Web posted at: 11:00 p.m. EST (0400 GMT)

In this story: Navy finishes mapping debris field Other jackscrews arrive for inspection Details of jackscrew investigation RELATED STORIES, SITES

From Correspondent Carl Rochelle

WASHINGTON (CNN) -- National Transportation Safety Board investigators have found additional damage to a mechanical part suspected in the crash of Alaska Airlines Flight 261 last January, which killed all 88 people aboard.

The NTSB said Friday that threads had been stripped from a gimbal nut that helped control the aircraft's horizontal stabilizer and on the lower stop nut, and there were impact marks on the outside of both nuts.

VIDEO CNN's Carl Rochelle looks at the focus of the inspections of MD-80 series aircraft. (February 18) Real 28K 80K Windows Media 28K 80K     INTERACTIVE RESOURCES Zoom in: How the MD-83 stabilizer works Timeline of recent crashes Flight 261 altitude data Image gallery: The crash of Flight 261 Flight 261 background Facts about Alaska Airlines     MESSAGE BOARD Alaska Airlines crash

"The board will try to determine if those impact marks -- as well as the stripping of both nuts' threads -- were made before the aircraft contacted the water or after," NTSB Chairman Jim Hall said in a statement.

Investigators also say now that the lower stop nut was stripped of its thread.

The plane, an MD-80 series, had radioed Los Angeles International Airport reporting trouble with its horizontal stabilizers just before it crashed into the Pacific on January 31. The horizontal stabilizers control an airplane's pitch, allowing its nose to point up or down.

Navy finishes mapping debris field

Also, the NTSB said the U.S. Navy has completed mapping the wreckage area off the California coast and has been directed to accelerate salvage operations next week.

In addition to the gimbal nut, investigators in Washington are studying the jackscrew assembly that it was attached to. The gimbal nut works with the jackscrew to control the up and down movement of the horizontal stabilizer.

Investigators are trying to determine how the gimbal nut threads were stripped and why strips of metal were found wrapped around the jackscrew.

"You can look at the metal," said aviation consultant Lee Dickinson. "You can look at the material and get an idea of whether something was pre-existing or whether something was a result of the crash itself."

Details of jackscrew investigation

Sources familiar with the investigation said the jackscrew assembly on the Alaska Airlines plane was believed to be the original unit, installed when the jet was built.

Investigators want to know if there may have been a damaged batch of jackscrew assemblies at the point of manufacture, or if maintenance practices such as lubrication may have contributed to the problems.

The board said it will also be examining grease samples from each unit to identify specific products being used and to determine compatibility between those products and to detect possible contamination. The work is expected to take several weeks.

They're also looking at the effects that extreme temperature changes might have on the mechanical parts. Flight 261 was flying a route from Puerto Vallarta, Mexico, to San Francisco when it crashed.

Other jackscrews arrive for inspection

Hall also said the NTSB will examine five newly received gimbal nut-jackscrew assemblies discovered to have problems during last week's FAA mandated inspection of more than 1,000 MD-80 series jetliners in the U.S. commercial fleet. More suspect assemblies were expected to arrive.

The assembly on Flight 261 was supplied to McDonnell Douglas by the Peacock Company of Norwalk, California, on June 28, 1990 The entire jackscrew assembly was manufactured and assembled in the United States, contrary to earlier reports.

As the Navy operation to bring up other parts of the plane accelerates, the remaining parts of the tail section and flight controls attached to the wings and cockpit area are among the sections of the aircraft expected to be recovered.

So far, the remains of 49 of the 88 people aboard the plane have been recovered from the ocean and identified by the Ventura County Medical Examiners Office, according to officials.

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