At what altitude must crew members use supplemental oxygen if flying above?

Crew members are required to use supplemental oxygen when flying above 12,500 feet, but this requirement varies based on the duration of the flight at that altitude. Specifically, for altitudes above 12,500 feet up to 14,000 feet, supplemental oxygen must be provided for any crew members that are on duty for more than 30 minutes.

Above 14,000 feet, all crew members must use oxygen continuously while at that altitude. At 15,000 feet and higher, the regulations stipulate that not only crew members but also passengers must have supplemental oxygen available if they are above that altitude for an extended period.

The choice of 12,500 feet aligns with these regulations meant to ensure safety and adequate oxygen levels for pilots and crew, preventing hypoxia, which can severely affect performance and safety in flight.