United Airlines 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.
United Airlines grounded its fleet of MAX 9 aircraft on Saturday, following a decompression accident aboard an Alaska Airlines flight that involved a door plug being blown away from the aircraft body during its ascent for a flight.
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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, told TPG Monday afternoon that it had not yet begun inspecting its grounded MAX 9 aircraft, so it wasn’t clear whether the airline would find similar defects. The airline said earlier in the day that it was awaiting further information from the FAA before beginning the process.
On Saturday, the FAA ordered the grounding of some 737 MAX 9 aircraft pending inspection.
In an Emergency Airworthiness Directive, the agency ordered the inspections of all aircraft that were outside of certain routine maintenance inspection windows, which will include about 171 aircraft, the agency said. There are approximately 215 of the aircraft subtype in service globally, according to aviation data firm Cirium.
The grounding came after Alaska Airlines flight AS 1282, departing from Portland International Airport (PDX) on route to Ontario, California (ONT), experienced a cabin depressurization Friday evening.
The left aft-wing “door plug” was blown out from the aircraft as the jet continued its departure climb. The force of the decompression was enough to pull smartphones from passengers’ hands, open the cockpit door and rip the pilots’ headsets off, National Transportation Safety Board (NTSB) chair Jennifer Homendy, who is leading the investigation, said in a briefing on Sunday, Jan. 7.
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Flight attendants were able to quickly secure the cabin and pilots descended and safely returned to Portland. There were no major injuries among the 171 passengers and six crewmembers. The two seats next to the door plug were unoccupied, which Homendy described as “very, very fortunate.”
The 737 MAX 9 features a spot for an extra emergency exit, which is required on models of the aircraft with certain higher-density seating configurations. Airlines that put fewer seats on the aircraft, such as United and Alaska, 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 plugs are secured by effectively just four bolts, along with other hardware, the NTSB said.
Alaska Airlines operates 65 of the MAX 9 aircraft, while United’s fleet includes 79 of the type.
Both airlines cut flights on Monday due to the groundings, with United canceling roughly 200 flights (about 7% of its mainline schedule) and Alaska scrubbing about 140 flights (20%).
United said on Monday that it expects “significant” cancellations through at least Tuesday, Jan. 9, although it had been able to avoid about 30 daily cancellations by switching to different aircraft types.
The findings harkened back to the nearly two-year global grounding of the 737 MAX type, which was implemented in April 2019 following the second of two fatal crashes involving the relatively new aircraft type.
Investigators attributed the crashes to a flight control system that was designed to pitch the aircraft down in some situations to compensate for the fact that the MAX has larger engines than the previous model of 737, the Next Generation, or NG.
The system, Maneuvering Characteristics Augmentation System (MCAS), was found to rely on a single “angle-of-attack” sensor, which feeds information about the aircraft’s pitch to the pilots and flight control computer. Without a backup sensor or other monitoring systems in place, if that sensor became damaged, investigators found that the plane could erroneously pitch down and cause the pilots to lose control.
Since the episodes, Boeing has found itself under a spotlight for its safety practices and records. Other potential manufacturing defects in various plane types — including the MAX — have been found since the grounding.
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