CHICAGO (Reuters) - Southwest Airlines Co said on Thursday it was extending the removal of Boeing Co 737 MAX aircraft from its flying schedule through Sept. 2, after the plane was grounded worldwide following two deadly crashes.

FILE PHOTO: A number of grounded Southwest Airlines Boeing 737 MAX 8 aircraft are shown parked at Victorville Airport in Victorville, California, U.S., March 26, 2019. REUTERS/Mike Blake/File Photo

Southwest, the largest global operator of the MAX with 34 jets, had previously said it was cancelling flights through Aug. 5. The revision is in line with American Airlines Group Inc’s recent decision to extend MAX cancellations through Sept. 3, from Aug. 19 previously.

Airlines worldwide are awaiting regulatory approval for a software fix and pilot training updates by Boeing that would pave the way for the jets to fly again after two deadly crashes here in Indonesia and Ethiopia triggered a worldwide grounding.

The Federal Aviation Administration said on Wednesday it did not have a specific timetable for allowing the MAX to resume flying.

Boeing has not yet conducted a certification test flight that is required before it can submit the software fix and training upgrade for approval, but has been discussing proposed changes with airlines and the FAA.

“We are encouraged by the reported progress and proposed path forward for returning the aircraft to service, and we remain confident that, once certified by the FAA, the enhancements will support the safe operation of the MAX,” Southwest said.

Once the FAA approves the MAX for flight, Southwest has said it would take about 30 days to get the jets up and running again.

The Dallas-based carrier’s schedule revision will keep about 100 flights out of its total peak daily schedule of 4,000. Southwest is notifying and accommodating customers affected by the amended schedule, it said.

Without enough airplanes to meet passenger demand, MAX operators are bearing revenue losses and cost increases after having had to cancel thousands of flights during the peak U.S. summer travel season.

On Wednesday, American Airlines Chief Executive Doug Parker said he believed it was “highly likely” that the MAX would be flying again by mid-August. He said the decision to keep the planes off the airline’s schedule into early September merely reflected monthly scheduling plans for crew.