LOS ANGELES (AP) - Two major airlines ordered visual inspections on a part of the tail assembly in their MD-80 and MD-90 jetliners Wednesday after investigators recovered that section from the wreckage of Flight 261 and found it to be damaged.
The component, called a jackscrew, drives the horizontal stabilizer, the focus of the investigation into the Jan. 31 crash that killed 88 people off the coast of Southern California.
Alaska initially said the inspections were prompted because the NTSB found the jackscrew to be stripped, but retracted part of the statement about an hour later.
''What we're saying is that the jack from the aircraft has been recovered and was found damaged,'' said Alaska spokesman Ray Prentice.
The precautionary inspections on Alaska's 34 MD-80 jets, all visual and all to be completed by the end of the day Wednesday, were expected to cause minimal schedule delays, spokesman Greg Witter said.
American said it would take a week to complete inspections on its 284 MD-80s and MD-90s.
''This voluntary inspection should alleviate public concerns following the Alaska Airlines accident,'' American Vice Chairman Bob Baker said.
The Federal Aviation Administration has not told airline companies to make additional checks of the tail section of MD-80 series aircraft, but that could change as the investigation evolves, said agency spokesman Paul Turk.
''We can't speculate on any action we might take, if any,'' he said. ''If the continuing education of the accident reveals any threat to the safety of flight, we won't hesitate to do whatever is necessary.''
More than 1,100 MD-80 aircraft are flown by nearly 70 airlines worldwide, making it one of the most popular commercial jetliners ever built.
A two-foot section of Flight 261's jackscrew was found with the main wreckage about 10 miles offshore, the National Transportation Safety Board said Wednesday.
''We do not know if it was stripped. We do know it was damaged. We do see ... those shreds or whatever that is around the screw. And our metallurgist is going to try to identify the origin of them,'' said Ted Lopatkiewicz, deputy director of public affairs at the NTSB.
''It was unclear whether the damage was pre-impact or from hitting the water,'' said National Transportation Safety Board Chairman Jim Hall.
The jackscrew is powered by two motors and resembles the corkscrew-like device that opens many automatic garage doors.
Investigators are focusing on the stabilizer, a wing-like device on the jet's tail, because pilots reported problems with it after taking off from Puerta Vallarta, Mexico.
If the jackscrew was damaged during flight, the horizontal stabilizer could move beyond its normal range, causing the tail wing to stall, or lose its lift, said William Waldock, associate director for the Center for Aerospace Safety Education at Embry-Riddle Aeronautical University in Prescott, Ariz.
It would be nearly impossible to recover from such a stall, Waldock said.
The pilots would not be able to control the up-or-down pitch of the aircraft - which would be consistent with flight data that shows the plane went into a 3.4-mile nosedive and radar tracking that shows something may have fallen off the plane as the dive began.
The stabilizer moves up and down as the nut rides the jackscrew back and forth, explained aviation analyst John Nance of Tacoma, Wash. It was unknown if the NTSB recovered the nut.
''The system somehow came apart, separated or whatever and the stabilizer was free to flip up into the wind at a very severe angle,'' he said.
''You put something like that directly into the wind at such an angle and it's going to fail. In the process of failing, instead of just coming off the airplane, it pulled the tail up and pulled the nose down,'' Nance said.
The plane's autopilot was disengaged when the jetliner reached 29,000 feet. The jet was flown manually for one hour and 53 minutes. Pilots say it is unusual to fly manually for that long and could suggest a problem with the autopilot or any number of other systems.
The pilots spent at least the last half hour of the flight troubleshooting a stabilizer problem.
''Those poor guys did everything they possibly could. They did it by the book, as far as I can tell, and it looks like the books failed us,'' Nance said.
Officials said the MD-83 had two maintenance write-ups last fall for problems with the horizontal stabilizer. In October, the system was checked and the plane returned to service. A month later, mechanics replaced a switch.
In Ventura County, the medical examiner said Wednesday no additional remains had been recovered, but nine passengers had so far been identified through dental records, fingerprints or tattoos.