On January 5, 2024, an Alaska Airlines Boeing 737 MAX 9 made global headlines, when a door plug blew off while the aircraft was inflight. This caused the FAA to temporarily ground the Boeing 737 MAX 9, so that regulators could investigate what happened. The jet is now flying again, but with updated inspection guidelines.
Given the Boeing 737 MAX’s history, there have been a lot of questions about what caused this incident. At first we wondered if there was a bigger issue with the 737 MAX 9, or what could cause a door just blow off while inflight?
Well, the National Transportation Safety Board (NTSB) has just published its preliminary findings regarding this incident, and the cause is exactly what had been rumored in recent weeks.
In this post:
Boeing forgot to install bolts on 737 MAX 9 door plug
While it’s worth reading the entire 19-page NTSB report about what happened, let me summarized what caused this incident:
- Spirit AeroSystems manufactures the fuselage of the 737 MAX 9; the door plug was manufactured in Malaysia on March 24, 2023, and was sent to Spirit AeroSystems’ Wichita facility on May 10, 2023
- The door plug was installed and rigged on the fuselage, and then shipped to Boeing on August 20, 2023, arriving at Boeing’s Renton facility on August 31, 2023
- On September 1, 2023, records show that a report was written about five damaged rivets on the edge frame forward of the left door plug; in order to repair this, four bolts had to be removed from the door plug
- The rivets were repaired correctly, but then the door plug was re-installed without the four bolts, which is obviously the major issue that caused this mess
- The NTSB notes that “the investigation continues to determine what manufacturing documents were used to authorize the opening and closing of the left MED plug during the rivet rework”
Even at this point, Boeing hasn’t been able to provide any documentation about who opened and closed the door plug, how it was done, and with what authorization. While this isn’t contained in the NTSB report, a whistleblower previously claimed that this slipped through the cracks because Boeing has a process failure whereby it uses two separate systems to record what work has been completed.
The systems obviously aren’t in sync, and that’s what caused this. Still, one has to wonder if the people putting the door plug back on without bolts knew something wasn’t right, or if this is such an easy mistake to make?
I’m not sure if this is a good or bad update
On the one hand, I suppose it’s good news that there’s not actually an additional, consistent problem with the 737 MAX, but rather there was an error that can easily be traced.
On the other hand, how the heck does an aircraft manufacturer have a process in place whereby a repair is performed, four bolts are missing, and there are no quality control measures in place? Even a month after the incident, Boeing still doesn’t know who performed this repair work?
How is that even remotely excusable for a company that is the United States’ largest exporter, and which has been producing planes for decades? And how is it possible that this is the process after Boeing got so much scrutiny regarding the 737 MAX, after it was grounded for nearly a couple of years?
There are still quite a few questions, though, even beyond accountability surrounding who installed this door. For example, 737 MAX 9 operators performed inspections on aircraft following the incident in recent weeks, and many found loose bolts. Are those loose bolts normal, since that seems to be different than this situation, where the plane was just missing four bolts?
The NTSB has now released its preliminary report into the Alaska Boeing 737 MAX 9 incident, where a door plug blew out. We now know that when the fuselage of this particular jet was sent from Spirit AeroSystems to Boeing, there was an issue with some of the rivets that required a repair.
The repair required removing a door plug (and four bolts), but somehow the people performing the work forgot to install the bolts once the work was complete. While there are supposed to be quality checks in place, those just didn’t happen, as it seems that Boeing has a bit of a paperwork issue.
I can’t decide if it’s reassuring to think that there’s not a bigger issue with the aircraft, or terrifying to think that Boeing’s quality control is so poor.
What do you make about the preliminary NTSB report about the 737 MAX 9 incident?