I think it's 12,500' in the US. Here's the regulation:CodyValkyrie wrote:I thought you were required to have oxygen inboard for anything over 10,000.
"§91.211 Supplemental oxygen
(a) General. No person may operate a civil aircraft of U.S. registryâ€â€
(1) At cabin pressure altitudes above 12,500 feet (MSL) up to and including 14,000 feet (MSL) unless the required minimum flight crew is provided with and uses supplemental oxygen for that part of the flight at those altitudes that is of more than 30 minutes duration..."
The regs get pretty fancy about that topic after that bit, but 12,500' is the cut-off! I did some flying at 11,500' in an unpressurized Piper Seminole without blacking out during some multi-engine training, for reference.
-Ian C