A federal inspector assigned to monitor American Airlines Group Inc. failed to act on safety complaints after developing a friendship with a company official, according to a government watchdog report.

The Federal Aviation Administration inspector, who had been assigned to the carrier for 28 years and had taken an overseas trip with an airline manager, didn't address what was later shown to be a legitimate tip about how the carrier assured aircraft were safe following maintenance work, the report said.

Concerns raised by American's pilot union, the Allied Pilots Association, went largely unaddressed for more than 18 months, according to the report, which was obtained by Bloomberg News.

The FAA's oversight of American's flight-test program "lacked objectivity," the report said. The FAA inspector, who has retired from the agency, wasn't named in the report.

The report by the Transportation Department's Inspector General puts a focus on how well FAA is overseeing safety at air carriers at a time when the agency has stressed cooperation with airlines rather than issuing fines or taking other enforcement actions.

After the compliance issues were raised by the Inspector General, the FAA brought in a special audit team last fall to review American's flight-test program and found it wasn't following the airline's written manuals, a violation of aviation regulations, according to a presentation summarizing the review. The agency also reassigned the inspector, the report said.

The FAA's review found pilot training records at the American program were "vague and inconsistent" and training materials were limited, said the presentation, which was provided to Bloomberg. It also concluded that hazards in the program had been identified previously, "yet not effectively mitigated."

American has cooperated with the review, put the flight-test group under new leadership and began a "top-to-bottom internal review," the airline said in a statement. "Last week, we notified the FAA that we have taken action to address and implement nearly all of the recommendations made in order to follow best practices and strengthen the safety of the program," the airline said.

The findings are reminiscent of a scandal a decade ago involving the FAA after inspectors at Southwest Airlines Co. lodged whistle-blower complaints because their manager had allowed the airline to skip critical safety checks. In 2009, a year after congressional investigators revealed the lapse, Southwest agreed to pay a $7.5 million fine to FAA.

Unlike the Southwest case, the agency addressed the issue in the American investigation once the IG brought it to higher ranking officials, according to the report. The FAA has agreed with all seven of the IG's recommendations and promised to implement them within a year, according to the report.

The latest investigation focused on a small team of pilots at American who were assigned to test planes after major maintenance or if planes were damaged and couldn't carry passengers. No customers are on such flights.

Concerns about the program, based in Tulsa, Oklahoma, had been raised by pilots and forwarded to FAA. However, the reports were investigated by an agency inspector who didn't take action, according to the report's findings.

That inspector had developed a close friendship with American's manager overseeing the flight program and their families socialized together, the IG report concluded. They also took a trip overseas together, the investigation found.

"We continue to work with management to ensure this non-compliance is corrected," said Dennis Tajer, a spokesman for the pilots union. "We look forward to seeing quick and thorough correction to what the FAA has pointed out as deficiencies."

The IG's report, expected to be formally released later this week, comes as the watchdog is separately looking at broader maintenance issues at American and Allegiant Airlines according to a May 9 announcement.

The FAA in 2015 introduced what it called its Compliance Philosophy, a program designed to improve safety by boosting airlines' own internal reviews and improving trust. Carriers that voluntarily report their own safety lapses and address them can avoid enforcement actions by FAA under the program.

The program follows similar cooperative efforts in place since the 1990s to allow pilots, mechanics and controllers who self-report inadvertent errors to avoid FAA enforcement actions. The data from their reports are studied to help prevent accidents.

However, some lawmakers have raised questions about whether FAA is being tough enough on airlines.