FAA chief says ‘we’ve sort of stopped trying’ to predict when Boeing Max 9 flights will resume

The Federal Aviation Administration (FAA) administrator has cast doubt on the Boeing 737 Max 9's near-term future after manufacturing errors were discovered during extensive inspections of the aircraft.

FAA Administrator Michael Whitaker said Wednesday that Boeing's manufacturing plants “will remain open” until the agency can confirm that the planes are being built safely.

Boeing's investigation began earlier this month after a door plug on a 737 Max 9 jet exploded mid-flight over Oregon, causing rapid depressurization and an emergency landing. No one was injured in the incident, but it prompted extensive testing of other 737 Max 9 aircraft, which found loose bolts and other manufacturing defects.

All similar 737 Max 9 aircraft have been grounded nationwide pending the inspection process. Whitaker said he has no idea when planes will be able to take to the skies again.

“It's hard to predict, so it seems like we've stopped trying,” he said. told CNBC. “But as soon as the problem is resolved, things will go back to normal.”

Whitaker said each FAA audit of the aircraft took more than eight hours, twice as long as the FAA originally anticipated when announcing the inspections.

“It took a lot of measurements,” he said. “Once that area is exposed, we want to understand bolt tensions and clearances and things of that nature. So we needed more data than usual because we really wanted to understand the problem.”

The scrutiny of the 737 Max 9 is also impacting airlines. United Airlines CEO Scott Kirby said Tuesday that he was “disappointed” by the incident and said the airline may look to other manufacturers for future aircraft purchases.

“We are Boeing's largest customer in the world. They are our largest partner in the world,” Kirby said in a separate CNBC interview on Tuesday. “We need Boeing to succeed…but they consistently have manufacturing challenges and we need to take action together.”

He added that he was confident the aircraft would be safe once the inspection was completed.

“To the FAA's credit, they worked with us on weekends and late at night, even in the weeds,” Kirby said. “So I think we're nearing the end of the line on this issue and the planes will be safe, but I'm disappointed that manufacturing challenges continue to occur at Boeing. This is nothing new.”

Boeing's stock price fell nearly 20% this month on the news.