a handle moves l-shaped arms called locking sectors up against the c-latches to keep them in place. in addition, there are pins up and down both sides of the door. normally, all of this holds the door shut, but in the case of united flight 811, something goes horribly wrong. forensic analysis of the door indicated that there was actually a short circuit. it s an electrical problem that had caused unexpectedly a command to unlock the door, to actually come open. so that it was a design issue. finding that cargo door was obviously critical to answering this question. it was so critical that the national transportation safety board actually reissued the report with a different and more up-to-date cause as well as causing all 747s to be redesigned to prevent this kind of failure from occurring again. so, it was a case where the industry learned a very valuable