Saw a comment somewhere from someone who claimed to have worked on aircraft doors & door plugs. Basically, the point was that the door/plug is designed to be held in place by the pressurized air inside the cabin, which is higher than outside air pressure when the plane is in flight. Thus, the loose nuts are (in principle) irrelevant, and could not have caused the blowout of the door plug.
If that comment is correct (sounds reasonable, but who knows?), then the door plug problem could be much more serious than a few untightened bolts.
Oh well! Spirit & Boeing can just hire a few more DIE staff and all will be under control.
But that assumes the door is fixed on its latch points near the top and the bottom so its edges align with the fittings on the fuselage and make a pressure seal. If the door is permitted to move up vertically, it will disengage from these latch points and fittings, and then the cabin air pressure will act to blow it outward, which is what happened.
The bolts which restrain vertical movement of the door (and which are protected by castellated nuts and cotter pins) serve to prevent this vertical movement that could cause the door to disengage. This is explained in the two videos in comment #20.
Can we impeach Homendy for her lies about transparency:
“Because this is an active investigation, we must receive permission from the NTSB to provide information about the aircraft and its prior maintenance,” Alaska Airlines said. “We have asked for permission from the NTSB to address these questions – they will not permit us to comment at this time. We will provide information as soon as the NTSB gives us permission to do so.”
“Now one of the NTSB’s core values is transparency.”
I am not following this story enough to know the details, but my first impression is that releasing details without finishing an investigation is prudent. People have a bias to make conclusions based on limited out of context information.
Chris Brady of the Boeing 737 Technical Channel has posted a Frequently Asked Questions video with additional information on how the plug door is held in place when installed normally, the functioning of the locking bolts preventing vertical motion which would disengage the door, (the lack of) warning indications on the flight deck for door open, the operation of the pressurisation system and fail-over modes, and the opening of the cockpit door when the cabin depressurised.
Juan Browne (Blancolirio) presents an update on FAA investigation of Boeing quality problems going beyond the specifics of the Alaska Airlines door loss and the class action lawsuit against Spirit Aerosystems, the contractor who manufactures the 737 airframe for Boeing.
Here is the complaint in the Spirit Aerosystems class action [PDF]. This is the FAA letter to Boeing [PDF] requesting information regarding the “circumstances [which] indicate that Boeing may have failed to ensure its completed products conformed to its approved design and were in a condition for safe operation in accordance with quality system inspection and test procedures.”
Apparently the interior is installed along the Boeing assembly line. At a minimum, the person attaching the interior panel over the door plug should have seen a lack of bolts. At a maximum, the door plug would have been removed at some point to aid insertion of equipment, and then should have been re-bolted.
Also, at this time, the 737 interiors are worked on some more. Sidewalls, seats, lavatories, and galleys are installed along the assembly line at this stop.
It is strange that this one simple the question has not been answered. From when the relevant fuselage section leaves Spirit until the aircraft makes its first revenue flight is the plug door ever opened?
If yes, we know the cause was not Spirit failing to properly install the bolts, nuts, or Cotter pins and we have a new clear suspect.
There also is the question of who covers the plug door with the trim panel. The answer is not necessarily damning. If there is evidence that the hardware was missing at the time, that represents an additional failure.
About 11,660 B-737 planes have been delivered in a variety of models. (Caution: That is a Wikipedia number – but let’s run with it for now). All of those planes had multiple doors, but probably only some of them had door plugs. Probably around 50,000 doors/plugs in total. The failure rate on doors/door plugs has clearly been very low. So what changed now?
It could be design changes, materials changes, subcontractor changes, training/staffing changes, quality control changes, DIE. Often disasters turn out to be the consequence of multiple successive failures, which is why they are in reality rare events. But whatever the sequence of failure(s) was, there is only one company which is accountable – Boeing, which was responsible for delivering a safe airplane to the customer. And the person who bears individual responsibility for the failure is the CEO of Boeing.
If he were Japanese, he would have committed seppuku. But he is a paid-up member of the US Ruling Class - so he will probably suffer only a 1% reduction in his hefty annual bonus.
