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A government hearing into an Alaska Airlines crash that killed all 88 people aboard ended Saturday night with investigators questioning the safety of a critical part used in the popular MD-80 and DC-9 series of jetliners. 

“We’re just gathering evidence to see where the safety deficiencies are,” John Hammerschmidt, who conducted the National Transportation Safety Board’s four-day hearing into the Jan. 31 crash, said in an interview. 

“There may be other aspects to the investigation that are not readily apparent from this hearing,” he said. 

The board plans to continue its investigation, with a conclusion on cause of the crash and recommendations expected in several months. It also can reopen the hearing if it chooses, Hammerschmidt told participants. 

From the start, the hearing focused on airline maintenance problems and the failure of a 21/2-feet-long jackscrew that helps control up-and-down movement in the tail wing of the McDonnell Douglas MD-83 aircraft. 

Saturday’s testimony dealt with the adequacy of Federal Aviation Administration’s procedures for monitoring of MD-80 and DC-9 jetliners, and why, as the NTSB’s Benjamin Berman put it, the FAA “didn’t pick up on these systemic problems.” Flight standards director Nick Lacey said the FAA is studying itself to determine just that. 

“We are learning through this process,” Lacey said at the hearing’s end. 

For the victims’ families, who hugged during breaks and taped photos of loved ones to chairs, the hearing was an often tedious exercise in accountability. 

“It’s very surreal. It feels really like this unbearable parade of if-onlys” said Emily Barnett, 37, of Bellingham, Wash., who had relatives on the flight. 

Spokesman Lou Cancelmi said the airline was satisfied with the hearing. “We want to find out what happened so that it never happens again,” he said. 

The jackscrew’s threads were found stripped and investigators suspect Boeing-approved Aeroshell 33 grease might have corroded the threads, or the jackscrew was left without lubrication because of a mechanical malfunction or the grease was improperly mixed with Mobil 28 grease, causing both to break down. 

U.S. Navy tests found the Aeroshell 33 grease was “contaminated” with Mobil 28 and contained aluminum-bronze particles from a stripped 8-inch gimbal nut. 

“Two incompatible greases should not be mixed because an inferior product could result,” the Navy reported. And Boeing engineer Dennis Jerome acknowledged: “There may be a chemical reaction between the two greases.” 

Boeing took over McDonnell Douglas in a 1997 merger and approved the airline using Aeroshell 33. But it was the only airline that did so on MD-80s, NTSB investigator-in-charge Richard Rodriguez noted. 

About 2,100 of the DC-9s and their MD-80 successors are in use, making them the world’s second-most popular models. The Boeing 737, with more than 3,000 in service, is the No. 1 plane. 

FAA experts and a Boeing engineer testified the jackscrew was found to be lacking grease, an assertion the airline hotly disputed. An FAA metallurgist said a tube that put grease on the jackscrew was clogged. 

Airline officials acknowledged paperwork was incomplete, lacking proper signatures, for approving the July 1997 change in the type of grease used. One engineer blamed the lapse on a deceased former co-worker. 

A transcript of the pilots’ final 32 minutes showed they fought valiantly until the last moments of their fatal nose dive into the Pacific Ocean near Los Angeles. 

Testimony during the hearing turned up evidence the airline initially pressured the pilots not to land at Los Angeles and it could have learned about a problem with its jackscrews as much as seven months before the crash. 

But the airline’s computer programming that tracks mechanical trends did not warn the airline until three days after the crash that three of the MD-80 series two-engine jets needed jackscrews replaced in 1999. 

The airline’s maintenance director, Wright McCartney, said it was unclear whether an earlier alert would have prompted the airline to check all its jackscrews. 

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On the Net: 

National Transportation Safety Board site: http://www.ntsb.gov 

Federal Aviation Administration: http://www.faa.gov