RAYTHEON B200 — Taylor, TX

What happened

While performing a postmaintenance flight, the pilot heard a loud, high-pitched "screaming" sound emanating from behind the instrument panel. The pilot returned to the airport and radioed the mechanic regarding the loud sound. When the pilot brought the airplane to a stop, the sound diminished. With engines idling, the mechanic opened the door of the airplane to troubleshoot the malfunction. Cabin pressure existed when the mechanic attempted to open the entry door and the door "blew" outward. The door struck the mechanic's head. An examination of the airframe revealed that a vacuum line had separated from the vacuum controller at a T-fitting. The T-fitting was located in the area that the mechanic had worked in during installation of the vertical speed indicator. The disconnected line disabled the entire vacuum system and subsequently disabled the airplane's pressurization system outflow valve. Prior to the mechanic opening the door, the pilot reported turning the environmental controls off which stopped the in-flow of cabin pressure. However, because the vacuum system could not drive the safety valve open, the airplane remained pressurized. An examination of the door assembly and differential-pressure-sensitive diaphragm revealed no anomalies. Testing results conducted on the diaphragm were consistent with a new diaphragm. The door system met the certification requirements of 14 Code of Federal Regulations (CFR) Part 23. The Beech 200 has no means of alerting outside personnel that the airplane is still pressurized while on the ground other than resistance against the release-button, nor is it required to by 14 CFR Part 23. The Pilot's Operating Handbook onboard the airplane had not been updated. A current version of the checklist would have directed the pilot to verify a zero pressure differential during the after-landing checklist.

An editorial "what led to it / how to avoid it" analysis for this accident is generated separately and will appear here.