- 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.
- American Airlines said it was "shocked" to learn of the watchdog's review.
A federal watchdog is reviewing how the Federal Aviation Administration handles allegations of improper aircraft maintenance at two U.S. airlines.
The Department of Transportation's inspector general's office will examine complaints received by the FAA and its reviews of allegations of improper maintenance practices at American Airlines and Allegiant Air, the department said in a memo Wednesday.
A segment on the CBS program "60 Minutes" last month criticized Allegiant's safety record and lawmakers called for more oversight in the wake of the report.
The watchdog announced an audit 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.
Lawmakers raised the issue of how the FAA oversees airline maintenance. The inspector general's office said the regulator works with airlines to address the reasons for noncompliance with regulations instead of "emphasizing enforcement actions."
The new review 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.
Several lawmakers asked the watchdog to probe the FAA's oversight of Allegiant after media reports about the airline's safety record, the memo added.
"American Airlines was shocked to learn of the Office of Inspector General's review and we stand by our strong safety record," said American Airlines spokesman Ross Feinstein. "Our team is working to understand why we are part of its review."
Allegiant welcomes "any analysis of our operation and safety culture, at any time," spokeswoman Hilarie Grey said.
Shares of American fell 3.5 percent on Wednesday, more than other competitors. Allegiant shares ended the day down 2 percent.