U.S. aviation regulators last month threatened to ground more than three dozen Boeing 737 planes that Southwest Airlines bought from foreign carriers over a lack of safety and repair documentation, according to a letter from the Federal Aviation Administration that was made public on Monday.
The issues, reported earlier by The Wall Street Journal, trace back to what the FAA said were required documents for 88 planes in question, which Southwest purchased from 16 foreign carriers, according to a U.S. Senate committee that released some of the documents and is requesting more information from the agency.
The planes make up about 11% of Southwest's fleet of roughly 750 Boeing 737s.
Southwest has completed the FAA's tasks for most of the planes but has yet to provide documentation on 38 more that are still flying.
Last year, the airline "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," said Southwest spokeswoman Brandy King.
The FAA gave the carrier two-years to complete a "nose-to-tail" physical inspection of the planes to confirm the repairs made by the planes' previous operators, she added.
An FAA official, John Posey, who oversees the airline, complained in an Oct. 29 letter to Southwest's COO about the slow pace of Southwest's review of the planes. The agency wanted the company to outline issues the planes encountered, including bird strikes, lightning strikes, hard landings or uncontained engine failure.
"If the FAA's concerns are not adequately addressed, the FAA may exercise remedies up to and including grounding the aircraft" until Southwest complies, the letter said.
Southwest told the FAA it would ramp up inspections to complete them by Jan. 31, instead of a deadline of July 1, 2020, the Senate Committee on Commerce, Science and Transportation said.
"Our continuous assessment of the ongoing inspections has revealed nothing to warrant the expedited timeline, but we remain on track to have all aircraft involved inspected by the end of January," said King.
"In response, the FAA communicated to congressional committees of jurisdiction that it believes Southwest Airlines is taking the FAA's concerns seriously and that revoking the airworthiness certificates of the uninspected aircraft is unnecessary," it said in a statement.
The paperwork issues led the airline and the FAA to develop a backup inspection and verification program, according to the documents. Southwest told the FAA it had 50 employees examine 63,000 repair documents in 15 languages, the Journal reported.