Not Enough Grease on Jackscrew

Putting to rest voluminous outside speculation about the cause of the crash of Alaska Airlines Flight 261, the NTSB is expected today to say what's been the popular explanation for nearly three years: not enough grease on the jackscrew caused the failure, which caused loss of control of the aircraft, and the deaths of all 88 aboard.

The flight, from Puerta Vallarta to San Francisco, went down January 30, 2000, off Point Mugu (CA).

Nearly immediately, as the wreckage was recovered (bottom photo), investigators turned to the horizontal stabilizer's jackscrew (right). When it was recovered along with its mating gymbal nut, it showed high friction and stripping, indicative of binding, which is indicative of insufficient lubrication.

Later, the issue of inspection came up, and many heads were put on the block. An inspection of the jackscrew called for replacement of the expensive assembly; four subsequent inspections showed the screw assembly to be in-tolerance, though just barely.

Further sleuthing revealed there had been two types of grease applied, at different times, to that jackscrew.

Both were approved greases; but there was a question of the compatibility of the greases -- could they work with each other, if mixed -- and the verdict was that they could not. Was the removal of the old grease thorough enough, to preclude any incompatibility? Would such incompatibility be sufficient to cause the wear and binding that brought the airliner down?

The NTSB's final report should put ANN's "Story of the Year 2000" to bed, and hopefully, to rest. From here, it's up to the lawyers to keep things so 'profitably' stirred up...

FMI: www.ntsb.gov/ntsb/brief.asp?ev_id=20001212X20339&key=1