No matter how you slice it, no matter how they try to blame the QA procedures at Boeing (and yes, that needs to be addressed) at the end of it, 4 workers took 4 bolts out of the door plug on a 737 airplane, did some maintenance, and failed to put the 4 bolts that were designed to keep the plug in place back into the assembly. . This was workers simply not doing their job, plain and simple. 4 people who could not make sure that the job was completed. Either too uncaring to finish a job, or deliberately not doing it to harm the company (they are lucky no one was hurt or killed) This could have been any number of critical assemblies….landing gear, engine attachment points, wing bolts, tail bolts, rudder cables, rudder hinges, etc. elevator bolts, etc…all of which are critical to safe and continued flight.
At the end of it, it was negligence by those workers that failed to complete their job and caused the door to depart the aircraft. (and, one wonders, where were the workers who put the interior on the door…were they blind or also uncaring?). Yes, again, there should have been an inspection afterwards, but if they were doing their job, that inspection should not have been needed. When you do a job and there are parts (bolts, nuts, and cotter pins, in this case) left over, one would think that even union employees would ask questions…..