Multiple airlines have discovered more loose Boeing aircraft parts. Regulatory authorities say that the investigation may expand to more aircraft models.

Last week, a Boeing 737 Max 9 aircraft operated by Alaska Air experienced a fuselage rupture incident, leading to the Federal Aviation Administration (FAA) grounding all Max 9 aircraft. The National Transportation Safety Board (NTSB) is currently conducting an investigation, and they are still trying to locate the four missing bolts. The NTSB has also indicated that they may expand the investigation to other Boeing 737 Max models, as several airlines have reported loose parts.

These bolts were originally used to secure the cabin door panel, but the panel suddenly became detached during an incident on January 5th. At the time, Alaska Air Flight 1282 was climbing to cruising altitude with 171 passengers on board. If properly reinforced, these bolts can prevent the door panel from sliding upwards and disengaging from the aircraft fuselage, which requires the panel to pass through 12 detents.

Clint Crookshanks, an engineer from the NTSB, stated during a press conference on Monday evening: "We have not yet found the four bolts that are used to limit the vertical movement of the door panel. We have not determined if they exist. This will be confirmed when we bring the parts to our laboratory in Washington, D.C."

Prior to the FAA grounding the Max 9 and requiring airlines to inspect these aircraft, Alaska Air and United Airlines discovered loose bolts. The regulatory authority in India also reported finding a missing washer on one of the aircraft.

NTSB Chair Jennifer Homendy stated on Monday that the NTSB will consider expanding the investigation to other 737 Max models. Media analysis suggests that this move will lead to a more in-depth scrutiny of Boeing and its manufacturing processes. This is a setback for Boeing, as the company is trying to get the 737 Max 9 back into service and avoid a prolonged grounding.

Homendy said during the press conference: "We need to first understand what happened with this aircraft. If we are facing a larger-scale problem or an issue with the entire model, we will issue urgent safety recommendations to drive change."

Following an 8% drop in stock price the previous day, Boeing's stock continued to decline on Tuesday. The U.S. stock market fell 2.3% in early trading on Tuesday, but the decline narrowed to 1% at midday, with the stock trading at $226.70. Spirit AeroSystems Holdings Inc., the supplier of the 737 Max fuselage, saw its stock price drop 3.3% in early trading, but the decline narrowed to 1.3%.

NTSB investigators have determined that the cabin door panel on the affected flight moved upwards before being pushed out and causing rapid depressurization. Normally, when bolts become loose, the roller guides allow the hinge panel or plug to swing outward, but these guides have fractured. These hinge panels are used for emergency exit doors on Max 9 aircraft, and airlines such as United Airlines and Alaska Air cover them because they are not needed in their seat configurations. Ryanair, one of the largest customers of Boeing 737 Max, has called for Boeing to "improve quality control," according to the company's CEO, Michael O'Leary, in a media interview. In December last year, Boeing requested airlines with the Max aircraft to inspect the rudder area for loose parts, as one airline had discovered a missing nut, and Boeing also found a loose nut on an undelivered aircraft.

The 737 Max model is a cash cow for Boeing, and CEO Dave Calhoun hopes to increase production this year. Data shows that Boeing received a total order of 369 aircraft in December, a record high, including 301 orders for 737 MAX aircraft, also a record high. Boeing achieved its delivery target of 396 737 aircraft last year and aims to deliver a total of 528 aircraft in 2023, including 73 787 aircraft.