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(CNN Business) —  

Whistleblowers at the Federal Aviation Administration questioned whether Southwest Airlines improperly flew jets without full knowledge of their safety history, according to documents released Monday by a Senate committee.

The documents show that Southwest acquired 88 used jets from foreign airlines starting in 2013, and the FAA permitted Southwest to fly the planes. In May 2018 an FAA official discovered paperwork abnormalities.

The airline then conducted a more detailed audit and found 360 major repairs to the planes that it had not previously known about. The result is that “Southwest Airlines appears to have operated aircraft in unknown airworthiness conditions for thousands of flights,” the committee said in a statement.

The Senate Commerce Committee made the documents public Monday.

But Southwest (LUV) says the problem was with the planes’ previous owners’ record keeping, and questions about the planes’ safety have been answered to the FAA’s satisfaction. The airline insists that the planes are safe and that the problems were a miscommunication. Southwest (LUV) said it was not hiding problems.

“In 2018, the FAA and Southwest discovered a small number of repairs on a few of these 88 pre-owned aircraft that had been performed but not properly classified by the previous owners due to differences in language and repair criteria,” Southwest said in a statement.

The company said it has since conducted a “thorough audit” of all repairs on the planes in question.

“Our actions did not stem from any suspected safety concerns with the aircraft but were an effort to reconcile and validate records and previous repairs,” said Southwest. “Since that time, Southwest has completed the nose-to-tail inspection of 41 aircraft, and analysis of the findings does not indicate any adverse impact on continued safe operation.”

Southwest says it plans to inspect the 47 remaining aircraft.

But Senator Roger Wicker, chairman of the Senate Commerce Committee, sent an October 30 letter to the FAA in which he termed the discrepancy as “troubling” and said it “corresponds to concerns that have been brought to my attention by whistleblowers as part of my investigation into aviation safety.” He said he is continuing to gather facts into the matter.

The FAA disputed the whistleblower concerns, saying the airline “met the requirements for immediate inspection and risk assessments on these aircraft.”

Questions about the safety of the planes comes at Southwest and other airlines await permission to once again fly the 737 Max jets that have been grounded since March due to two fatal crashes that killed 346 people. Southwest has more of the 737 Max jets in its fleet than any other airline.