The Alaska Airlines plane that lost a piece of its fuselage in midair on Friday was not being used in long flights over water because a pressurization warning light had gone off during three recent flights, the National Transportation Safety Board said on Sunday.
Jennifer Homendy, the board’s chairwoman, said it was too soon to say whether the issue had played a role in the Friday incident, which led to the grounding of 171 Boeing 737 Max 9 planes in the United States. “It is certainly a concern and it’s one that we want to dig into,” Ms. Homendy said at a news conference in Portland, Ore.
She said Alaska Airlines maintenance workers had been instructed to determine why the warning light had repeatedly gone off, but the work was not done before the flight on Friday. Instead, Ms. Homendy said, workers reset the system and the plane was put back into service, though the airline restricted it from being used on flights to destinations like Hawaii.
She said the safety board was trying to get more information about what had happened during the three flights when the light went off, all of which had taken place since Dec. 7.
The Friday incident on Alaska Airlines Flight 1282, bound for Ontario, Calif., occurred at an altitude of 16,000 feet and forced the pilots to return to Portland International Airport soon after takeoff. None of the 171 passengers and six crew members aboard were seriously hurt, but they were exposed to howling winds from the hole in the fuselage as pilots made the emergency landing.
The authorities have focused their attention on a mid-cabin door plug, part of the piece of fuselage that was torn from the plane. Ms. Homendy said on Sunday that investigators had recovered the door plug from the backyard of a Portland home. Door plugs are used to fill emergency exits that are not needed because the plane is configured with fewer than the maximum possible number of seats.
Ms. Homendy also said that there was no information on the plane’s cockpit voice recorder because the device begins re-recording after two hours, erasing the previous data, and it was not retrieved in time. Ms. Homendy said the safety board, which has been pushing to expand the two-hour period to 25 hours, had conducted 10 investigations since 2018 in which the cockpit voice recorder was similarly overwritten.
“Cockpit voice recorders aren’t just convenient for the N.T.S.B. to use in investigations or the F.A.A. to use in investigations,” she said. “They are critical to helping us accurately pinpoint what was going on.”
Ms. Homendy said the force of decompression during the Friday incident blew the cockpit door open, causing one of the pilots to lose a headset. Head rests were detached from seats, seat backs went missing and clothes were scattered throughout the plane.
Sunday was the board’s first full day of investigation into the episode, which has drawn new attention to the Max aircraft and its troubled history. The Max was grounded worldwide after two Max 8 jets crashed within several months in 2018 and 2019, killing hundreds.
On Saturday, the Federal Aviation Administration announced mandatory inspections affecting 171 Max 9 planes being used by U.S. airlines. Alaska Airlines, which has 65 of the aircraft, canceled 170 flights on Sunday because of the order. United Airlines, which has 79 Max 9s, more than any other carrier, said it canceled about 270 flights over the weekend.