Southwest Airlines has canceled thousands more Boeing 737 Max flights, this time until at least November, after the Federal Aviation Administration recently discovered a new flaw in the plane’s flight software. The company’s announcement follows news that United and American Airlines are also delaying the reintroduction of the 737 Max until November.

The three US airlines have spent the last few weeks repeatedly announcing new cancellations as Boeing and the FAA work to re-certify the 737 Max, after it was involved in two fatal crashes within the span of five months that claimed 346 lives.

Boeing CEO Dennis Muilenberg said in a tweet Thursday that the plane’s grounding, which was ordered by regulators around the world in March, is “presenting significant challenges for our customers, company and supply chain.” Boeing also announced Thursday that it will take a $4.9 billion hit in the second quarter alone from the grounding of the flight, and that it doesn’t expect the plane to return to flight until the fourth quarter of the year. The company has set up a $100 million fund for the families and communities of the victims.

US airlines have spent the summer cancelling thousands of flights

The deadly crashes were largely caused by software that was supposed to prevent the newer 737 Max planes from stalling in certain situations. That software, known as Maneuvering Characteristics Augmentation System, or MCAS, made calculations based on readings from a single external sensor on the plane, and also had no way to know if that sensor was damaged.

This was the case in both of the crashes. What made matters worse was that pilots didn’t know what was happening, because Boeing hadn’t properly disclosed the software to airlines — partly to save money, but also to bring the 737 Max to market more quickly.

Southwest’s delay and Boeing’s financial disclosure come after families of the victims testified in front of the House aviation subcommittee this week. Paul Njoroge, who lost his wife, mother-in-law, and his three children, said at the hearing that the FAA “recklessly” let Boeing police its own safety policies. “The FAA should have known that the failure to have triple redundancy in critical safety systems could cause crashes and death,” he said.

The House Committee on Transportation and Infrastructure has launched an investigation into the FAA’s certification process, and US transportation secretary Elaine Chao convened a committee to do the same. Chao had also previously asked the Department of Transportation’s inspector general to examine the FAA’s certification process.