The Transportation Department Inspector General's office said in 171 of 185 of cases sampled, FAA inspectors accepted root cause analyses by American Airlines "that did not identify the true root cause of the problem" and the agency "closed compliance actions before the air carrier implemented its corrective actions."
The FAA said it "agrees with many of the recommendations in the report and is taking steps to address them."
American Airlines said it welcomed the report. "We plan to work with the FAA to ensure we take positive action and continuously refine and improve our safety controls," an airline spokeswoman said.
The report found that in one instance American "flew an aircraft with an inoperable emergency evacuation slide for 877 days before reporting the non-compliance to FAA."
American said it reported the slide issue as soon as it was discovered as part of its maintenance program that requires intentional slide deployments. It added it "then worked with the vendor to develop an audit system."
The report said that if American Airlines had categorized the slide as a more serious issue it would have prompted different corrective actions.
The FAA did not evaluate whether American's "risk ratings adequately captured the level of risk for these findings," the report found.
The report said "ineffective root cause analysis and the associated corrective actions may have contributed to a number of repetitive non-compliances" issues at American.
Without verifying corrective actions, "FAA cannot reasonably ensure that American Airlines is sufficiently identifying root causes and mitigating future maintenance non-compliances," the report added.
The FAA, it added, "could not verify whether the 73% of findings that American Airlines rated as 'low' or 'very low' were indeed low risk."
It also said FAA inspectors were not adequately trained on root cause analysis or how to review airline risk assessments.
(Reporting by David Shepardson; Editing by Mark Porter)
By David Shepardson