Hawker Beechcraft King Air B200, Taylor, Texas, April 10, 2008–The NTSB ruled that the probable cause of the accidental death of a mechanic was the failure of the pilot and mechanic to ensure that the airplane was fully depressurized before opening the cabin door. Contributing to the accident was a failure in the airplane’s vacuum system. While performing a post-maintenance flight, the pilot reported hearing a high-pitched noise in the cockpit, which diminished after landing. With the engines idling, a mechanic opened the cabin door, which blew outward and struck him on the head. Examination of the airframe revealed that a vacuum line was disconnected, disabling the turboprop’s pressurization outflow valve. The pilot’s operating handbook on board had not been updated. A current version of the checklist would have directed the pilot to verify zero pressure differential after landing.