On 24 September the FAA published a proposed rule that would raise the altitudes at which pilots in pressurised aircraft must wear an oxygen mask. Congress told it to look at Part 135 in the 2024 reauthorisation act. The agency is also rewriting the Part 91 text so the two parts do not end up the wrong way round on the safety continuum. For charter and on-demand flying with two pilots, the wear-a-mask floor would move from FL350 to FL410. A single pilot at the controls would don at FL350 rather than FL250. Under Part 91, aircraft with quick-donning masks could, if the proposal stands, fly to their certificated ceiling without one pilot wearing a mask throughout. Comments will follow the usual NPRM clock. This is not a final rule.
The FAA prices an oxygen service at $100-400 a fill. It counts about 4.7 million Part 91 and 135 turbojet and multi-engine turboprop operations a year and then says that for every one percentage point of those flights that no longer need a service, operators would save $4.7m–18.6m. That is a sensitivity, not a pledged annual dividend. How many flights actually stop needing a bottle change depends on how often crews now cruise in the band the new rule would free.
For a Part 135 charter shop the practical questions are route and crew. Higher usable cruise without a mask on one face can mean a more efficient flight level, less oxygen logistics and a slightly less awkward two-crew cockpit. It does not change time of useful consciousness after a rapid decompression. Quick-donning still has to work in five seconds. Owner-flown jets and corporate departments will count the same servicing line. They will also count whether their insurers and training manuals move as fast as the CFR.
The proposal is therefore a small change in physiology policy with a larger effect on how private and charter flying will factor it. Whether it is cheap or merely differently regulated will show up in fill invoices after the comment period, not in the Federal Register’s arithmetic.