Federal Aviation Administration inspector Mark Lund claimed in a memo poor maintenance at Northwest "jeopardizes life or property." Replacement workers and Northwest managers have been maintaining the airline's fleet since union mechanics went on strike Aug. 20.
Lund described an incident in which a maintenance manager couldn't find the right switches to check an engine on one plane, and another in which a replacement mechanic failed to properly test brakes on another.
Minnesota Public Radio News, which obtained the memo, reported the FAA reassigned Lund to administrative duties after Northwest complained.
Northwest and federal officials say the airline's fleet is safe. MPR said there are indications maintenance has improved since the early days of the walkout.
FAA spokesman Greg Martin says the FAA and the Department of Transportation's Office of Inspector General are investigating safety at the airline.
Martin said investigators are also looking into Lund.
"We had received complaints that the inspector was intimidating Northwest replacement workers, was unprofessional in his conduct and exceeded his authority," he said."
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