Alaska Airlines jet had three pressurization warnings before emergency landing

Alaska Airlines pilots reported pressurization warning lights on three earlier flights of a two-month-old Boeing 737 MAX 9 jet that made an emergency landing on Friday after a door plug tore off.

National Transportation Safety Board (NTSB) Chair Jennifer Homendy said late on Sunday the auto pressurization fail light illuminated on Dec. 7, Jan. 3 and Jan. 4, but she said it was unclear if there was any connection between those incidents and the rapid depressurization incident.

Alaska Airlines made a decision after the warnings to restrict the aircraft from making long flights over water to Hawaii so that it could return quickly to an airport if needed, Homendy said.

The Federal Aviation Administration (FAA) on Saturday ordered the temporary grounding of 171 Boeing MAX 9 jets installed with the same panel after the Alaskan Airlines plane was forced to make an emergency landing with a gap in the fuselage.

The missing door plug was recovered on Sunday evening by a homeowner who found it in his backyard, the NTSB said.

Homendy said the cockpit voice recorder did not capture any data because it had been overwritten and again called on regulators to mandate retrofitting existing planes with recorders that capture 25 hours of data, up from the two hours required at present.

She also painted a harrowing picture of the incident, saying the force of the decompression led to the cockpit door being blown open.

"They heard a bang," Homendy said of the flight deck crew. A quick reference laminated checklist flew out the door, while the first officer lost her headset. "Communication was a serious issue... It was described as chaos."

The door plug tore off the left side of an Alaska Airlines jet following takeoff from Portland, Oregon, en route to Ontario, California, forcing pilots to turn back and land safely with all 171 passengers and six crew on board.

"It must have been a terrifying event to experience," Homendy said.

Alaska Airlines said earlier in a response to questions about the warning lights that aircraft pressurization system write-ups were typical in commercial aviation operations with large planes.

The airline said "in every case, the write up was fully evaluated and resolved per approved maintenance procedures and in full compliance with all applicable FAA regulations."

Alaska Airlines added it has an internal policy to restrict aircraft with multiple maintenance write-ups on some systems from long flights over water that was not required by the FAA.

The FAA said on Sunday the affected fleet of Boeing MAX 9 planes, including those operators by other carriers including United Airlines, would remain grounded until the regulator was satisfied they were safe.

The FAA initially said on Saturday the required inspections would take four to eight hours, leading many in the industry to assume the planes could very quickly return to service.

But criteria for the checks have yet to be agreed between the FAA and Boeing, meaning airlines have yet to receive detailed instructions, people familiar with the matter said.

The FAA must approve Boeing's inspection criteria before the checks can be completed and planes can resume flights.

Alaska Airlines canceled 170 flights on Sunday and a further 60 on Monday and said travel disruptions from the grounding were expected to last through at least midweek. United, which has grounded its 79 MAX 9s, canceled 230 flights on Sunday, or 8% of scheduled departures.

The accident has put Boeing back under scrutiny as it awaits certification of its smaller MAX 7 as well as the larger MAX 10, which is needed to compete with a key Airbus model.

In 2019, global authorities subjected all MAX planes to a wider grounding that lasted 20 months after crashes in Ethiopia and Indonesia linked to poorly designed cockpit software killed a total of 346 people.