Watchdog probes FAA's oversight of aircraft maintenance at American Airlines and Allegiant Air© Provided by CNBC The Department of Transportation's Inspector General said it was expanding an audit it announced last year.

  • The watchdog will review FAA's independent reviews and the complaints it receives from its hotline.

A federal watchdog is auditing the U.S. airline-industry regulator over how it handles allegations of improper aircraft maintenance at two airlines.

The Department of Transportation's Inspector General's office will examine complaints received by the Federal Aviation Administration and the FAA's routine reviews of allegations of improper maintenance practices at American AirlinesAAL and Allegiant AirALGT, the watchdog's office said in a memo on Wednesday.

The watchdog announced a review of how the FAA reviews airlines' maintenance practices in June 2017. In February, it said it planned to focus on the two carriers after an analysis of complaints sent through an FAA hotline. The audit also aims to find out whether the FAA "ensures that Allegiant and American Airlines implement effective corrective actions to address the root causes of maintenance problems," said Wednesday's memo.

"The FAA is continually working to enhance safety for the flying public and is never content with the status quo," the FAA said in a statement, adding that it welcomed the review. "This system is designed to identify potential risks before they become serious problems and ensure that corrective action is taken."

Allegiant Air shares tumbled last month after a "60 Minutes" segment criticized the airline's safety record.

Allegiant said it also welcomed "any analysis of our operation and safety culture, at any time." American Airlines did not immediately respond to a request for comment.

Shares of American were down 2.6 percent in afternoon trade, lower than its large-airline competitors. Allegiant shares were off 3.1 percent.

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