Airlines in a Crisis

When its a set screw A set screw is fully threaded while a bolt is only partially threaded. (And yes a set screw has a head. If no head its called a grub screw.) This means a bolt fits better and thighter in its holes than a set screw does. A set screw only have the sideways or bending strength of a bolt 1 size down.  A bolt can only be thigthened to a certain point because it runs out of threads. Who knows if Spirit used set screws securing the plugs on a couple of planes because they ran out of the correctly sized bolts and expected Boeing to redo them anyway. Impossible to see/inspect unless you draw/remove the item in question. Or the head is stamped with a part number and you can see the head. Should Boeing have overengineered it so that a bolt also was covered by a sleeve that double secured the bolt wasn't overtightened and drew the frames closer, weakening them in the progress. A sleeve would also protect the bolt from the roller pins it was supposed to keep in place consta...

Further investigation points to that Spirit the maker of the 737 airframes do ship it with this blank in place but only temporarily fastened. Boeing then take the blank out to load the interior and then reinstall it.  The blank is like a door with a larger window and no manual opening mechnism and is being held in place by a frame rail with lugs but instead of movable pins and a handle like a normal door it is held in place with bolts and castelated nuts that should have split pins in them. As long as they are in place the doorblank can not be moved upwards (some say downwards and some later pictures of a locking bolt seems to support this) to a position where it can be opened / taken out. Again, regular inspection of these bolts have been made inpossible by having a complete panel on the inside. Questions remains over if split pins where installed. Bolted on parts can have the nuts unwinding themselves due to vibration. And the exact torque required to prevent this can be difficul...