Oxygen for glider pilots

The regulation is four lines long and easy to satisfy. The problem is that it was written for aircraft that pass through altitude, and a glider does not pass through anything — it sits at 14,000 feet for three hours, alone, cold, working hard, and then has to fly an approach at the end of it. The legal minimum is a floor. It was never a plan.

7 min readAnyone flying high, and anyone planning to

What the regulation says

14 CFR 91.211(a), for unpressurized aircraft, in three bands:

  • Above 12,500 ft MSL up to and including 14,000 ft MSL — the required minimum flight crew must be provided with and use supplemental oxygen for that part of the flight at those altitudes which is of more than 30 minutes duration.
  • Above 14,000 ft MSL — the required minimum flight crew must use supplemental oxygen during the entire flight time at those altitudes.
  • Above 15,000 ft MSL — each occupant of the aircraft must be provided with supplemental oxygen.

Three things in that text are worth pulling out, because each one is regularly misread.

Three details in the wording

"Required minimum flight crew" means you. In a single-seat glider there is no ambiguity and no one to share the responsibility with. In a two-seater being flown by one pilot, the passenger or the second pilot who is not required is not covered by the first two bands at all — which is exactly the gap the third band closes, and it closes it at 15,000 rather than at 12,500.

"Provided with" is not "uses". Above 15,000 the regulation requires that oxygen be available to every occupant. It does not, on its face, require the passenger to use it. As a description of what you should actually do with a person sitting behind you who has never been at altitude before, that is obviously inadequate, and no sensible pilot treats it as guidance.

"Cabin pressure altitude" is not what your altimeter reads. Your glider is unpressurized, so cabin pressure altitude is simply pressure altitude — what the altimeter shows with 29.92 set.

Flying on a local altimeter setting on a low pressure day, your pressure altitude is higher than your indicated altitude. The gap is usually small, it is not always small, and it runs in the unhelpful direction: you can be legally required to be on oxygen while the instrument in front of you reads below the threshold. Our density altitude calculator converts an altimeter setting and elevation to pressure altitude if you want to see the size of it on a given day.

Why the numbers are not a plan

91.211 applies to every unpressurized aircraft in the United States, from a Cub to a King Air. It is not aimed at anything, and in particular it is not aimed at a flight profile that looks like this: five or six hours aloft, most of it above 10,000 feet, cockpit temperature well below freezing, single pilot, no autopilot, continuous decision-making, and an approach and landing at the end when you are tired.

Set that against a typical powered flight that climbs to 12,000, cruises for forty minutes and descends. The regulation treats them identically. They are not identical.

The relevant point is not that hypoxia arrives suddenly at some altitude — it does not — but that it arrives gradually, that its earliest effects are on judgement and on the willingness to notice that judgement is impaired, and that duration matters as well as altitude. Night vision measurably degrades a long way below any of these thresholds. None of that is controversial and all of it is documented by the FAA and by AOPA, whose material on this is good and worth reading in full.

Which is why experienced wave pilots commonly set their systems to begin delivering oxygen at around 5,000 feet — not because anyone requires it, but because on a long high flight the cost of doing so is a slightly shorter bottle duration and the benefit is arriving at the top of the climb, three hours in, still thinking clearly. That is a personal decision and we are not making it for you. We are telling you that people who do a great deal of this make it that way.

Constant flow versus pulse-demand

This is the equipment decision that most affects what you can actually do with a bottle you can carry in a glider.

A constant flow system does what the name says: oxygen flows continuously at a rate set for the altitude. Most of it is delivered while you are exhaling, which is to say most of it is wasted. It is simple, cheap and reliable, and it is what the club's shared bottle usually is.

A pulse-demand system — the electronic delivery systems most soaring pilots mean when they say EDS — senses the start of each inhalation and delivers a metered pulse of oxygen at that moment only. Nothing is delivered while you breathe out. The gain is not marginal: for a given cylinder, endurance changes by a large factor, which is precisely what converts a bottle small enough to fit in a glider into a bottle that lasts a wave day.

That is why the soaring world standardised on demand systems while much of general aviation did not. The flight profile makes the difference decisive.

The equipment questions worth asking

  • What is on the cylinder's stamps? Cylinders carry test dates and, for some types, a life limit. An out-of-test bottle is not a paperwork inconvenience; it is the reason the shop will refuse to fill it, usually on the Friday before the good weekend.
  • Cannula or mask? A nasal cannula is far more comfortable for hours at a time and is conventionally limited to lower altitudes — commonly cited as below 18,000 feet. Above that, a mask. Check the limitation that applies to your specific equipment rather than the number in this sentence.
  • Aviation oxygen? Use what your equipment and your supplier specify. This is a genuinely settled question with a genuinely boring answer, and it is not one to improvise on.
  • How do you know how much is left? In flight, in gloves, in the cold. If the answer involves craning round to read a gauge behind your shoulder, solve that on the ground.
  • Have you got a pulse oximeter? They cost very little, they clip on a fingertip, and they replace a guess with a number at the exact moment your judgement is the thing in question. It is the highest-value item on this list per dollar by a wide margin.

The pre-flight nobody does

Oxygen is the one system in a glider that you cannot check by looking at it, cannot fix in the air, and will not miss until you are already impaired enough not to miss it. Three things, before the good wave day rather than on it:

  1. Contents, in advance. Not on the grid. A bottle that needs filling on Saturday morning is a bottle that does not get filled.
  2. Flow confirmed, not assumed. That the system delivers, that the cannula or mask is connected, that the demand unit's battery is good.
  3. Reachable and secured. A cylinder that shifts in flight is a loose object in a small cockpit, and the fittings are not designed to be struck.

Where we stop

This page explains a regulation and the equipment used to comply with it. It is not medical advice, and altitude tolerance varies enormously between people and between days for the same person — smoking, dehydration, illness, fatigue and age all move it, and none of them announce themselves.

If you are planning to fly high regularly, the two things worth doing are reading the FAA's own material on hypoxia in full, and — if you can get to one — an altitude chamber or reduced-oxygen training session. Reading about the symptoms is not the same as recognising your own, and the entire difficulty with hypoxia is that the faculty you need in order to notice it is the first one it takes.

If you run a club and this does not match your experience, we would genuinely rather hear it. Corrections make this better and we will credit you.

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