The 737 Max is Boeing’s best-selling jet ever and is expected to be a major driver of profit, with more than 4,500 of the planes on order. The company’s shares have fallen about 11 percent this week.
“We are supporting this proactive step out of an abundance of caution,” Boeing’s chief executive, Dennis A. Muilenburg, said after the grounding was announced. “We are doing everything we can to understand the cause of the accidents in partnership with the investigators, deploy safety enhancements and help ensure this does not happen again.”
After the Indonesian crash, pilots’ unions complained that pilots had not been made aware of a change to the flight-control system on the Max that could automatically push the plane’s nose down in certain situations. That software change is believed to have played a role in the Lion Air crash and may have been a factor in the Ethiopia accident as well. Boeing is now planning to roll out a software update that has been in the works since the Indonesian crash.
The introduction of a consequential new flight-control feature without any requirement for pilot training is now drawing more scrutiny. Representative Peter A. DeFazio, Democrat of Oregon and the chairman of the House transportation committee, said in an interview that he planned to conduct an investigation into the F.A.A.’s certification of the 737 Max, with a focus on why the regulator did not require more substantial training for 737 pilots learning to fly the new version.
Mr. DeFazio said he expected to seek all relevant communications between Boeing and the F.A.A., among other documents, and was willing to use subpoena power if necessary. “This warrants vigorous investigation,” he said. “We’re going to get anything in writing there is to get.”
Airlines in the United States stood behind the planes up until the F.A.A.’s order, and even expressed confidence in the jets afterward. Southwest Airlines said in a statement that it had been in “constant contact” with the F.A.A. and Boeing since the Ethiopian Airlines crash and that it remained confident in the 737 Max aircraft after flying the planes for more than 88,000 hours over 41,000 flights without incident. American said, “We continue to have the utmost confidence in our fleet.” The groundings in the United States and elsewhere also affected Boeing’s Max 9 model, which United Airlines flies.
“I don’t want to hazard a guess,” Mr. Elwell said when asked how long the Boeing planes might be prohibited from flying. “My hope is that the F.A.A., the carriers, the manufacturer, that all parties will work very hard to make this grounding as short as possible so that these airplanes can get back up in the sky.”