NTSB: Lack of Grease Brought Down Plane


WASHINGTON, D.C. – The National Transportation Safety Board concluded yesterday that inadequate lubrication of a horizontal stabilizer component caused the crash of an Alaska Airlines plane that killed 88 people off the coast of California three years ago.

In wrapping up an investigation that brought an unusual amount of attention to airframe maintenance, the board blamed the Seattle-based airline for inadequately greasing a jackscrew that helps control movement of the stabilizer – a tail assembly that determines the angle of flight.

The whole system is based on people doing what theyre supposed to do, Acting Chairman Carol J. Carmody said during a hearing at the Safety Board’s headquarters. In this case, Alaska Airlines failed to do that. Among thoseattending were several dozen relatives and friends of the passengers who died.

The board also faulted the Federal Aviation Administration for allowing Alaska Air to reduce its frequencies of lubricating the jackscrew and of checking it for excessive wear. The panel rejected Alaska Airlines arguments that the use of Shells Aeroshell 33 Grease contributed to the excessive wear of the jackscrew.

Early in the investigation, Alaska Airlines charged that the jackscrew may have worn out early because of the use of Aeroshell 33 – which was recommended by manufacturer Boeing beginning in 1997 – or by mixing of Aeroshell 33 with Mobilgrease 28, which had been recommended previously. The Safety Board investigated those claims, and indeed recommended that industry do a better job of developing and identifying airframe greases. But after commissioning extensive tests on the performance of the two greases in question, as well as mixtures of them, investigators concluded that selection of greases had nothing to do with the excessive wear.

Alaska Airlines Flight 261 crashed Jan. 31, 2000, during a flight from Puerta Vallarta, Mexico to Seattle, and the NTSBs investigation soon centered on the stabilizer and jackscrew. The MD-83 models horizontal stabilizer – which controls the pitch of flaps making up the forward section of the tail wing – had jammed shortly after takeoff. This caused difficulty with the planes ascent but the pilot then achieved a stable flight pattern.

The crew managed to jar the stabilizer loose as the plane approached a stopover in San Francisco but doing so precipitated a 7,000-foot dive. The pilot then leveled the plane and maintained tenuous control for the next eight minutes, during which the crew decided to land in nearby Los Angeles. When the pilot tried to descend, however, the plane dove again and fell 17,000 feet to the ocean.

The Safety Board said both dives were caused by failure of the jackscrew, which raises and lowers the stabilizer by rotating through a stationary acme nut. Excessive wear had nearly worn off the screws threads; when those remaining were stripped,the first dive occurred,officials said. At that time, a retaining nut was all that kept the screw from passing all the way through the nut. The second dive occurred when the force on the screw broke off the retaining nut.

Safety Board staff said it was obvious that the jackscrew failed because of inadequate lubrication; search crews recovered the two-foot rod and found no grease at the interface with the acme nut. Investigators said the Alaska Airlines mechanic who performed the last scheduled maintenance on the plane did not appear to have a complete understanding of how to grease the stabilizer and probably did not perform the procedure adequately.

But they also said that inadequate greasing on that single occasion would not by itself have caused the excessive wear incurred by the jackscrew. They noted that Alaska Airlines had been cited several times previously for having inadequate maintenance programs.

The best we could say is that there was either no lubrication or inadequate lubrication earlier in the history of that jackscrew, Office of Aviation Director John Clark said.

Board members agreed that Alaska Airlines decision to lengthen the interval for changing grease in the stabilizer contributed to the inadequate lubrication of the component. They also cited the airliners decision to lengthen the interval for checking the screws condition, saying this reduced opportunity for detecting excessive wear.

The airline informed the FAAboth times it changed the intervals,but the agency did not object. NTSB board members said this amounted to a lack of oversight by the administration, a conclusion that drew applause frommany of the passengers relatives.

The FAA is the government and I think the public trusts the government to ensure the safety of flight, Carmody said. I feel in this instance the FAA failed miserably.

Alaska Airlines issued a statement yesterday saying it did not agree with all of the Safety Boards findings but added that it would be insensitive to surviving family membersto debate the issues now.

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