Gulfstream IV / G350 / G450
Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Flight Instructor
Flight Crew Last 90 Days 115; Flight Crew Total 5800; Flight Crew Type 500
Human-Machine Interface; Training / Qualification
Aircraft Equipment Problem Critical; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance
Flight Crew Returned To Clearance; General Declared Emergency; General Maintenance Action
Aircraft; Human Factors
As we were climbing through FL350; the cabin altitude started to climb. I put on my oxygen mask; contacted ATC and told them I needed to descend immediately. I was cleared to FL240. As the cabin altitude rapidly climbed through 14;000 FT I initiated an emergency descent; declared an emergency and requested a lower altitude. I was re-cleared to 11;000 FT. As a result of my rapid rate of descent; I descended 300 FT below my assigned altitude as I leveled off but immediately climbed back up to 11;000 where we were given a heading while we assessed the situation. None of the passengers or crew was injured. We cancelled the emergency and continued to our destination at a lower altitude. Closer to our destination we diverted to another airfield for maintenance. In the future I would try to start arresting my descent rate earlier in order not to descend below my assigned altitude. Today I realized the importance of the use of oxygen masks at high altitude and the training that we receive regarding emergency descents. I am very thankful for both. Without oxygen this situation could have ended up much worse.
While making an emergency descent due to a loss of pressurization at FL350 the flight crew of a G-IV descended 300 FT below their cleared altitude of 11;000 MSL before recovering.