Southwest 737 MAX 8

Southwest Airlines on Thursday became the first airline to respond to the latest setback for Boeing’s 737 Max, extending its cancellation of flights scheduled to operate the embattled aircraft through October 1.

Southwest, which operates the most 737 Max planes of any U.S.-based airline, said it is a move that will cancel 150 flights per day. But by making the decision now, it will cut down on last-minute flight cancellations and allow it to switch aircraft and re-book passengers more easily.

“We offer our apologies to our customers impacted by this change, and we thank them for their continued patience,” the airline said in a statement.

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The Boeing 737 Max was grounded in March after separate crashes just months apart on Lion Air and Ethiopian Airlines killed 346 people. Preliminary reports showed that a new stabilization system forced both planes into a nosedive from which the pilots could not recover.

Boeing has been working on the issues and thought it had a fix for the apparent problem completed in May, but the FAA this week discovered yet another issue with the 737 Max during simulation testing.

The FAA did not elaborate on the extent of the issue, but sources told CNN that the new flaw was a microprocessor failure that could cause the same problem—forcing the nose downward. “It was difficult for the test pilots to recover in a matter of seconds,” one of the sources told the network. “And if you can’t recover in a matter of seconds, that’s an unreasonable risk.”

American, United, Delta and other major airlines will likely follow Southwest’s lead and cancel their flights at least until October 1 in the wake of the latest news. All U.S. carriers have set at least three dates to try and take to the air again with the plane, the last being by Labor Day.