Gulfstream V / G500 / G550
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 35; Flight Crew Total 19000; Flight Crew Type 3500
Fatigue; Other / Unknown
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Overcame Equipment Problem
Human Factors; Aircraft; Environment - Non Weather Related
During high altitude cruise on an extended range international trip; the flying crew elected to stop using the O2 masks and to hold them in our laps because the mask 'comfort position' was inoperative and it was causing headaches and unnecessary fatigue to both crew members due to the tight fit. As soon as the aircraft was able to meet adequate fuel reserves at the destination; we descended to FL410 to complete the trip. The PIC was in the crew rest area during this time period. The FAA should consider a change to this rule as the corporate aircraft being manufactured now spend most of their time at or above FL410. The masks are not made to be used for so many hours at a time; many aircraft have an Automatic Descent Mode (ADM) in the autopilot and wearing the O2 masks increases flight crew fatigue on what are often extended duty days.
G550 First Officer laments the requirement to use oxygen continuously above FL410; especially when the comfort position of the mask is inoperative; believing that the Automatic Descent Mode (ADM) in the autopilot should eliminate the requirement for both pilots to be on oxygen.