The Federal Aviation Administration has given Southwest Airlines Co. time until the end of the year to replace unauthorized parts on more than 50 of its jets.

Southwest Airlines Co., the largest low-fare carrier, said the replacement program would not change its flight schedules.

Last month federal investigators discovered that the company was using some unauthorized parts in its planes and ordered the company to fix the problem until Tuesday. Then the airline filed an application and received an extension until December 24 to complete the job.  

The Company claimed that it had already replaced unauthorized parts on over 40 of the 82 planes since Aug. 21 when FAA officials had discovered the problem.

Aviation Safety Institute’s Mike Overly said, "The inspection and parts issues are a shame for Southwest, which currently has a zero-onboard fatality record and should be working hard to maintain it."

Southwest Airlines got a set back in March when it had to a $7.5 million fine to settle allegations that it operated nearly 60,000 flights without the required inspections.

In the recent trading shares in Southwest Airlines closed at $8.02, down 2 per cent on the NYSE.