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[...] why did the left hand (LH) mid-exit door plug blow off of the 737-9 registered as N704AL? Simple- as has been covered in a number of articles and videos across aviation channels, there are 4 bolts that prevent the mid-exit door plug from sliding up off of the door stop fittings that take the actual pressurization loads in flight, and these 4 bolts were not installed when Boeing delivered the airplane, our own records reflect this.
As a result, this check job that should find minimal defects has in the past 365 calendar days recorded 392 nonconforming findings on 737 mid fuselage door installations (so both actual doors for the high density configs, and plugs like the one that blew out). That is a hideously high and very alarming number, and if our quality system on 737 was healthy, it would have stopped the line and driven the issue back to supplier after the first few instances.
The mid-exit doors on a 737-9 of both the regular and plug variety come from Spirit already installed in what is supposed to be the final configuration and in the Renton factory, there is a job for the doors team to verify this "final" install and rigging meets drawing requirements. In a healthy production system, this would be a "belt and suspenders" sort of check, but the 737 production system is quite far from healthy, its a rambling, shambling, disaster waiting to happen. As a result, this check job that should find minimal defects has in the past 365 calendar days recorded 392 nonconforming findings on 737 mid fuselage door installations (so both actual doors for the high density configs, and plugs like the one that blew out). That is a hideously high and very alarming number, and if our quality system on 737 was healthy, it would have stopped the line and driven the issue back to supplier after the first few instances. Obviously, this did not happen. Now, on the incident aircraft this check job was completed on 31 August 2023, and did turn up discrepancies, but on the RH side door, not the LH that actually failed. I could blame the team for missing certain details, but given the enormous volume of defects they were already finding and fixing, it was inevitable something would slip through- and on the incident aircraft something did. I know what you are thinking at this point, but grab some popcorn because there is a plot twist coming up. [....]
(Score: 5, Interesting) by janrinok on Thursday January 25 2024, @12:19PM
That is true, but the door assembly is delivered as a complete item which Boeing then fitted. The responsibility for the door assembly rests with Spirit who signed it off as meeting all technical requirements. That is how I understand the source and subsequent links.
It is, if you will, Boeing being held responsible for fitting a black box which had a loose circuit board inside it. Boeing are not expected to open every black box and check the internals. However Boeing are on the hook for having rather dubious fault tracking and agreeing to accept a description of the work which resulted in some checks after the work was completed having never been carried out.
Either way, the reporting does not fill one with confidence.