Citation II S2/Bravo (C550)
Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 100; Flight Crew Total 8500; Flight Crew Type 2000
Aircraft Equipment Problem Critical
Flight Crew Diverted; General Declared Emergency; General Maintenance Action
Aircraft
The aircraft was level at FL370 for over an hour. A rather loud whistling noise was heard. I observed the cabin climb rate jump from 0 to +3;000 FPM. We were experiencing a rapid depressurization. I declared an emergency with Center and requested an immediate descent. We began a descent immediately. Center was very helpful in giving me directions to various airports. Oxygen masks were donned by pilot and passengers; passengers were briefed; and we made a course reversal toward [nearest suitable airport]. As we proceeded; we leveled the aircraft at 14;000 FT with ATC approval. At that point; the cabin was holding at 3;000 FT. Oxygen masks were removed. The emergency status was canceled. I told ATC that we no longer needed priority handling and that we could be sequenced onto an arrival and an approach normally. We changed our destination as we considered maintenance availability at various airports. The approach and landing were normal. There were (to my knowledge) no conflicts with other aircraft. Center personnel responded promptly to all of our requests. I never heard any transmissions that would indicate that our situation/actions affected other aircraft (no heading or altitude changes were given). The emergency was handled promptly; professionally; and decisively by both myself and ATC personnel. Maintenance was performed [and] it was discovered that the right-hand pressurization check valve had failed. Instead of air being sent into the cabin to pressurize the aircraft and inflate the door seal; the air was allowed to escape into the right-hand nacelle. The flight resumed two days later.
C-550 Captain (single pilot) reported loss of pressurization at FL370. Emergency was declared; a descent executed; and a diversion to an appropriate airport followed; where a pressurization check valve was found to have failed.