I was doing a post servicing test flight on a Black Hawk (aircraft engineer) with my avionics counterpart when the pilot complained that the RH cargo door was unlocked (we were at about 3500'). The avionics lad (who didn't close the door properly in the first place) unbuckled from the RH Loadmasters seat, went down the back and knelt next to the door. Rather than just push it closed, he fully opened it then slammed it shut, scaring the **** out of me and the pilot in the front. All we herd was a sudden rush of air, a loud bang followed by a loss of comms and visual with the avionics lad! Needless to say he received another arsehole after we landed. On another flight over Brisbane many moons ago, another avionic guy was sitting in the RH loadmasters seat again taking photo's during a flypast when he accidently dropped his lens cover out the window. He quickly put his head out the window to see were it went and lost his headset for the effort.