No criminal wrongdoing has been established in connection with the Jan. 31 crash off the coast of California that killed 88 people, The Times said in a copyrighted story.
Citing three sources in two federal agencies, the newspaper said the Federal Bureau of Investigation and investigators from the Department of Transportation have been questioning Alaska Airlines employees as part of an inquiry into airline maintenance practices that has been under way for several weeks.
FBI spokeswomen Roberta Burroughs in Seattle and Debbie Weierman in Washington, D.C., would not confirm or deny the existence of any such investigation Saturday.
The U.S. Department of Transportation could not immediately be reached, and calls to the National Transportation Safety Board were not returned Saturday.
The Times said the FBI, which usually plays an advisory role to the NTSB, is conducting a separate, parallel investigation a course of action reserved for cases where there is evidence or suspicion of crime.
Alaska Airlines said it was not aware of a criminal probe.
"The FBI has been involved in the investigation of Flight 261 since the beginning,'' Alaska Airlines spokesman Jack Evans said Saturday. "Currently, we are unaware of any change in their role since the beginning. If there is a change in that role, we'll cooperate with them as we have been."
The criminal investigation grew out of a 15-month-old inquiry into practices at Alaska's maintenance facility at Oakland, Calif., the Times said. In that inquiry, 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.
But the plane that crashed "was not involved in the original request from the U.S. Attorney's Office for records related to aircraft," Evans said.
Earlier, the airline said it has put a top manager on leave while it investigates claims by 64 Seattle mechanics that they were "pressured, threatened and intimidated'' to cut corners on repairs.
Federal Aviation Administration and airline officials began interviewing the mechanics after the airline told the agency about the complaints, which came in a letter delivered to the carrier on Thursday.
Alaska Airlines 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.
NTSB Chairman Jim Hall said in a statement nearly all major components of the MD-80's tail section have been recovered and the agency announced the completion of its field study.
Hall also said investigators had found no grease on a crucial portion of the jackscrew that helped control the movement of Flight 261's horizontal tail stabilizer, lng 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 on its Web site Friday that the mechanics' letter was triggered by concerns over a recent repair to the horizontal stabilizer and jackscrew assembly on an Alaska 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.
A draft of the letter by 64 mechanics quoted by the Times 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."
In a statement, Alaska Airlines said about 12 mechanics had been interviewed and that it would immediately ground any planes found to be potentially unsafe.
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. 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 J. 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.