The B190 rear cargo door has 6 "C" type rotatable Cam locks 3 on each side of the door and 4 horizontal 3/4" slide pins that sit along the bottom that go thru massive strong 1/2' steel anchorholes in the fuselarge.
Should the cable operated Cam locks come undone (all of them at once I dont know how) but say a cable breaks and the pressure of the air on the door makes them vibrate around slowly the 4 massive pins at the bottom of the door which are put in place by a lockable handle and slide lengthways thru the big anchorholes will not undo unless the handle has not been clicked/locked into place. (there is also a pop out lock pin that has to be pressed in from outside to even move the handle into the unlocked position)
A vibration in a 1900 on t/o if the handle is not in the locked position may cause the handle to vibrate down and unlock thus also turning the 6 cable operated camlocks with it and presto door open!
If the door is open RED light at eye level is on (2 bulbs) so either it wasnt working and the crew didnt know the door was open, or they could have been on Com 1 Gnd pwr, not giving any lights on the warning panel untill the master switched on and if the door was closed cause the groundie gave the thumbs up they wouldnt see a light anyway.
Not sure on eagles sops about the bleeds, sometimes they can do a bleeds off t/o to maximise performance but at auckland intl they shouldnt use all the runway if they did a bleeds on t/o, its 200miles long!