SEATTLE (AP) _ Alaska Airlines has put a top manager on leave while it investigates claims by Seattle mechanics that they were ``pressured, threatened and intimidated'' to cut corners on repairs.

In a statement, Alaska Airlines said it would immediately ground any planes found to be potentially unsafe.

The airline said it had also notified federal prosecutors and the National Transportation Safety Board, which is probing the Jan. 31 crash of Alaska Flight 261 off the California coast in which 88 people died.

The complaints from the 64 mechanics were contained in a letter delivered to the airline on Thursday and quoted this week by The Seattle Times.

A draft of the letter said workers were directed to do things ``specifically contradicting'' federal aviation regulations, and alleged they had been ``pressured, threatened and intimidated ... in the daily performance of our work.''

During a recent repair on an MD-80 _ the same type of plane as Flight 261 _ mechanics said there told not to replace worn parts.

The airline and Federal Aviation Administration officials have begun interviewing the mechanics.

NTSB Chairman Jim Hall said this week that most major components of Flight 261's tail section have been recovered. He also said investigators had found no grease on a crucial portion of the jackscrew that helped control the movement of the jet's horizontal tail stabilizer, long a focus of the crash probe.

A spokesman for the plane's manufacturer said the part normally should be lubricated, but he refused to speculate about what the NTSB finding might mean.

The Times reported that the mechanics' letter was triggered by concerns over a recent repair to the horizontal stabilizer and jackscrew assembly on an MD-80 jetliner.

The mechanics allege the plane was fixed properly only after heated discussions.

FAA spokesman Mitch Barker said the agency was aware there had been recent ``debate'' at Alaska Airlines over a horizontal stabilizer repair. He said the plane was returned to service in proper condition.

Robert Falla, the leader of the airline's Seattle maintenance base, was placed on administrative leave, the airline said. He could not be reached by telephone, but his lawyer predicted he would be exonerated.

``Robert Falla has never knowingly allowed any aircraft to go into service that was not airworthy or (that) failed any safety standard,'' said a statement from his lawyer, Scott Engelhard.

The airline is already the subject of a criminal investigation over alleged maintenance violations at its Oakland, Calif., maintenance base.

A grand jury in San Francisco is investigating whether supervisors signed for repairs that weren't done or that they weren't authorized to approve.