Back in the 1980s I was at Hawker Pacific and we modified a number of B200s for the National Safety Council with inward opening doors. The aircraft could be depressurized and the door opened in flight. The idea was for deploying parachuters, once they jumped out the door was shut and the aircraft could be repressurised. I went on a number of the flights where we tested the process opening and closing the door. It might have been one of those Kingairs after the NSC was wound up - can't remember the time frame of that happening.
I often wonder what happened to those aircraft and if they're still operating.