Actually, in a pressurized aircraft such as the L39, the requirement is for a "quick-donning" mask at 25,000-35,000 feet. It doesn't have to actually be on unless the cabin is breached (cabin pressure reduced to an effective 10,000 foot or higher altitude). Above 35,000 feet, yes, all the time. The military may have its own rules, but 135.89 are the rules the FAA requires wherever it is authoritative. The assumption is that at 25,000 feet or below you can dump altitude down to 10,000 feet quickly enough to avoid hypoxia. The above is also Part 135, essentially for commercial passenger travel operations.Part 91 covers non-commercial general aviation operations, which have different standards. Nonpressurized cabins at 12,500 feet or less, no need, 30 minutes for the pilot without at 12,500-14,000, canula or similar for everyone above 14,000 feet. Canula are okay up to 35,000 feet. mask above (all assuming unpressurized cabins). For pressurized cabins, no requirement below 25,000 feet, quick availability for all aboard at 25,000-35,000 feet, mask worn above.(I'm a private pilot, and I get quizzed on this on every biannual flight review)Parachute jump operations are Part 91 not Part 135, so up to 14,000 feet there is no requirement for passengers, and the pilot gets up to 30 minutes before requiring oxygen at 12,500-14,000 (which for a parachute jump is generally not the case). There are more regulations about parachuting in Part 105, but those don't have to do with oxygen and pilots.I hadn't heard about anything speed-related. Do you have reference? I'd love to be able to pull an "unless!" on the examinerWanna buy your own? www.trade-a-plane.com/filtered… has 'em for about a quarter million... of course, maintenance and operations are going to be more expensive than your loan payments...