(CNN) -- A government report says poor FAA oversight allowed Southwest Airlines to put millions of lives at risk.
The U.S. Department of Transportation's Inspector General conducted the 18-month audit.
It was sparked by a whistleblower complaint about the FAA's oversight of Southwest and a "number of" operational issues at the airline, including pilot training deficiencies and inaccurate information being provided to pilots prior to flights departing.
The report found Southwest flew 88 planes it bought from foreign carriers without properly verifying their airworthiness.
The report said those planes flew more than 150,000 flights, putting more than 17 million passengers at risk.
Southwest says it's made significant progress in addressing the issues in the report. That includes enhancing the integrity of its weight and balance program.
And it says all of those "used" planes have undergone a comprehensive inspection or are currently being inspected.