What to know about the Boeing 737 MAX 9 and the MAX series

11.01.2024 - 16:47 / thepointsguy.com / Jennifer Homendy / Spirit Aerosystems

An Alaska Airlines flight departing Portland International Airport (PDX) on Friday night experienced a sudden cabin decompression as a fitting on its fuselage shot away from the plane, leaving a gaping hole in the airplane as frightened passengers scrambled to put on emergency oxygen masks.

The flight, AS 1282, bound for Ontario, California, safely returned to Portland with 171 passengers and six crew members, the airline said. Only a few minor injuries were reported. However, the force of the decompression was strong enough to pull smartphones from passengers' hands, open the cockpit door and rip the pilots' headsets off, National Transportation Safety Board chair Jennifer Homendy, who is leading the investigation, said in a briefing on Sunday.

On Saturday, the Federal Aviation Administration ordered the grounding of all 737 MAX 9 aircraft outfitted with a door plug aft of the wing. The NTSB found that the door plug had become unsecured on the Alaska Airlines flight, causing it to shoot off the jet and fall to the sky as the cabin rapidly decompressed.

The 737 MAX 9 features a spot for an extra emergency exit, which is required on aircraft models with certain higher-density seating configurations. Airlines that put fewer seats on the aircraft, such as Alaska and United Airlines, can choose to install a plug in its place instead.

The plug is installed by Spirit AeroSystems, which manufactures the fuselage for Boeing's 737 MAX aircraft in Witchita, Kansas, and ships the completed bodies to Boeing's Renton, Washington, factory for final assembly. The NTSB said that the plugs are effectively secured by just four bolts, along with other hardware.

United said on Monday that it had found installation defects during its inspections of the door plugs on Boeing 737 MAX 9 jets, including loose bolts.

The finding, which was first reported by industry outlet The Air Current ahead of United's confirmation, significantly raises the stakes of the nascent crisis for Boeing and its supplier that builds the aircraft fuselage and installs the plug, Spirit AeroSystems. The Air Current reported that at least five United aircraft had been found to have defects.

Alaska Airlines, the other major U.S. airline operating the aircraft subtype, said later on Monday that it had found similar loose hardware while preparing its planes for the formal inspections.

The grounding applied to about 171 MAX 9 aircraft, the FAA said. There are approximately 215 of the aircraft subtype in service globally, according to aviation data firm Cirium.

That compares to the 737 MAX 8, which has been the far more widespread of the two midsize 737 MAX models. Boeing has delivered 1,039 of the smaller MAX 8 to airline customers, according to Cirium