The office of the U.S. Department of Transportation’s inspector general will audit how the Federal Aviation Administration has investigated allegations of “improper maintenance practices” at Allegiant Air and American Airlines in response to requests from several members of Congress, it said Wednesday in a memo.

This is not a new audit, but rather a change in focus from a previous one requested by Democrats in Congress announced in June, 2017. At the time, the inspector general’s office said it wanted to judge the effectiveness of the FAA’s oversight on all U.S. airlines, asking whether recent mergers or cost-cutting had affected how safety regulators interact with carriers.

But the focus will now narrow to Allegiant and American, Matthew E. Hampton, assistant inspector federal for aviation audits, said Wednesday.

“During our initial audit work, we visited two air carriers and found that FAA had moved its oversight strategy from emphasizing enforcement actions to working with carriers to address the root causes for noncompliance of safety regulations,” the memo said. “We also found that the relationships and information-sharing practices between air carriers and their FAA oversight offices vary significantly.”

The FAA said in a statement it stands by its strategy for how it oversees U.S. airlines.

“This system is designed to identify potential risks before they become serious problems and ensure that corrective action is taken,” it said in the statement. “The process is dynamic and requires that the FAA, and the airlines we oversee, constantly strive for safety improvements.”

Allegiant has been in the news recently, with the CBS news program 60 Minutes investigating it last month for what it correspondent Steve Kroft said were lapses in its safety program, though the company has vigorously denied the allegations. In the memo Hampton said the government decided to focus on Allegiant and American before the 60 Minutes report aired, though he acknowledged some members of Congress became more interested in Allegiant after the April 15 television report.

It is less clear why American Airlines was included. American Airlines spokesman Ross Feinstein said he did not know why the FAA’s relationship with American is being investigated, and said American only learned of the inspector general’s audit on Wednesday.

“American Airlines was shocked to learn of the Office of Inspector General’s review and we stand by our strong safety record,” Feinstein said. “Our team is working to understand why we are part of its review. We welcome all oversight from the federal agencies involved in ensuring the safety of the traveling public and are proud of our partnership with the Federal Aviation Administration.”

A spokeswoman for Allegiant also said the airline will cooperate. “We welcome any analysis of our operation and safety culture, at any time,” she said.

In addition to reporting information about an unusually high number of safety-related incidents at Allegiant Air in recent years, 60 Minutes also focused on how the FAA was interacting with airlines. The report noted, as the inspector general’s audit memo said, that the FAA was increasingly working cooperatively with airline to try to fix problems, instead of fining them for errors. The FAA defended the practice, saying it produces results.

In his memo, Hampton said the inspector general’s office would examine whether working closely with airlines rather than fining them is effective.

Editor’s Note:This story has been updated to include comment from American Airlines.

Photo Credit: A Department of Transportation inspector general's audit will look at how the FAA has handled safety investigations at Allegiant Air and American Airlines. Pictured is an Allegiant Air Airbus A320. Airbus