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I recently watched this video:

When the controller realized the pilot was hypoxic (at about 9m47s in the video) they said,

Kalitta 66 if able descend and maintain FL260

but 26000 feet is still very high and provides insufficient oxygen. I (an ignorant student pilot) would not expect someone to recover from hypoxia at that altitude.

I realize it's possible the controller had other reasons to slowly descend the plane, but are there specifically aeromedical reasons for a gradual or slower-than-emergency descent into richer-oxygen air in this kind of situation?

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3 Answers 3

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There are no aeromedical reasons to descend slowly due to hypoxia.

Also, the controller did not know for certain that the pilots were hypoxic due to a loss of pressurization. All the controller knew was that they were in an emergency situation and seemed to be having difficulties.

The descent to FL260 was not gradual. It was a normal descent. The controller probably only controlled the airspace down to FL260, or there could have been another aircraft in the area at FL250. Kalitta 66 was further cleared to 11,000’ once clear of any conflicting aircraft. We didn’t hear the entire ATC conversation, but I bet Kalitta 66 was cleared to 11,000’ BEFORE they reached FL260, so in reality, it was probably a normal descent from FL320 all the way down to 11,000’.

An ATC controller can not order any aircraft, in any situation, to execute an emergency descent. ATC can only provide clearances and instructions to insure ATC separation. Sometimes a controller will ask a pilot to “expedite descent” but a pilot can only accommodate that request if it is safe to do so.

There is an old story about an ATC controller asking a pilot to expedite his descent and reach a certain altitude at a certain point. The pilot responded “unable”. The controller then said “Don’t you have Speedbrakes”? The pilot answered “Yes, I do, but speedbrakes are for MY mistakes, not yours”.

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    $\begingroup$ I got a chamber ride at DCIEM in Downsview in the early 80s, with a group of skydivers going for high alt jump certification. It was only a ride to 25000 ft to experience hypoxia symptoms, no decompression demo. My initial hypoxia symptom was tunnel vision, then euphoria. When I reconnected to oxy, the symptoms vanished in a couple seconds. My buddy was a chain smoker, and he went into nitrous oxide-like giggle fits within about a minute. When I was drawing my shapes on the clipboard, I remember they were lopsided, and I knew they were lopsided, but I didn't think that was a problem. Weird. $\endgroup$
    – John K
    Apr 30, 2022 at 4:39
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    $\begingroup$ Or that controller only owned the airspace down to ~FL260 (FL245 is a common boundary) and had to coordinate with another sector before giving lower. $\endgroup$
    – StephenS
    May 1, 2022 at 4:35
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    $\begingroup$ @JohnK there's a bit in this after 6:30 where he's told to put his mask back on and turn on the oxygen or he'll die, and he just says "I don't wanna die" then does nothing while sitting there smiling (controlled environment, not actually at risk). Very eye-opening. youtube.com/watch?v=kUfF2MTnqAw $\endgroup$
    – llama
    May 2, 2022 at 2:44
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    $\begingroup$ @llama I dimly remember reconnecting my oxy line by myself when a kind of drunken sensation welled up, intense enough to startle me (we were primed in the briefing to do that - the chamber tech in the box with us was a kind of safety backup). I kind of wished I'd let it go longer to see what happened. I've had nitrous at the dentist and the effect is similar. My giggly chum was totally out of it by a couple minutes in and had to be reconnected by the chamber tech (I think there were 6 or 8 of us in the box). $\endgroup$
    – John K
    May 2, 2022 at 12:43
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    $\begingroup$ @llama I watched it and I'd say I was like the first guy but I lasted longer, and my chum was like the host who had to to have the intervention, but as a heavy smoker he went into the goofy stage a lot sooner because I remember him giggling before I even noticed any symptoms. $\endgroup$
    – John K
    May 2, 2022 at 12:58
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You could say there is a "technical" aeromedical reason for descending slowly, not related to hypoxia directly, but you shouldn't be flying at all if it exists and there's no way a controller could know about it, and the pilot would likely not know about it either until he tries it anyway.

That would be sinus cavities that are unable to vent due to inflammation. Air escapes a lot easier than it can get in, so if you have blocked sinuses you will likely be unaware on the ride up as air is able to get out. The problem starts when it has to come back in.

The effect of 4 or 5 or 6 psi squeezing your sinus cavities is like a migraine x10. Unbelievably painful (I've experienced it descending from 8000 ft to 1000 ft with blocked sinuses I was unware of until the sensation of a freight train parking on my face started). This why every pilot should carry a bottle of a fast acting sinus decongestant like Otrivin in their brain bag.

Putting all that aside, I'd say that the controller, once he'd deduced what was going on, decided to coax the pilot down, knowing that if the pilot was in uphoria stage, the last stage before you pass out, he wouldn't respond to an attempt by the controller to raise alarm bells, and not having the authority to order the pilot to start an emergency descent, that was the only option available.

Probably the initial request of FL260 may have been an attempt at "baby steps" less likely to get the pilot confused or questioning with the first descent instruction and he gave it knowing he would modify it once they were established in a descent.

Of course the problem is the if the pilot had passed out right after starting the descent, with the ALT setting at FL260, the plane would have leveled off there as the autopilot captured the flight level, then slowed down (the engines being at idle) until the autopilot kicked off as the plane approached stall, then it probably would have eventually started a spiral dive until the crew came-to or the plane broke up. Hard to criticize the controller's decision in the heat of the moment though, and it worked.

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  • $\begingroup$ Yes, once wile descending I suddenly had a sensation of someone driving nails into my forehead, could not clear via "Vasalva" maneuver, fortunately was flying a powered plane not a glider, could solve the problem by climbing immediately, then continuing Vasalva maneuver. Never recurred again. And at other times have had no problem dealing (via Vasalva maneuver) w/ the much greater pressure changes associated w/ descending while swimming, snorkeling, or scuba diving. $\endgroup$ Apr 30, 2022 at 2:04
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    $\begingroup$ I just recently had Omicron, and the after effect was sinus inflammation, which I deduced because I was getting nasty headaches that I eventually realized were coming on when good weather approached, with maybe a 2 or 3000 foot equivalent altitude change as a high moved in. I couldn't tell other than the headaches from pressure changes. My doc prescribed a nasal steroid anti-inflammatory that cleared it up after a couple of weeks. $\endgroup$
    – John K
    Apr 30, 2022 at 4:45
  • $\begingroup$ Valsalva maneuver $\endgroup$ Apr 30, 2022 at 21:31
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There are no diving medical reasons limiting the descend speed of scuba divers as long as they are able to equalize their ears as fast as necessary. Descending from surface to 10 m depth with double surface pressure is possible in a few seconds.

Ascending to surface after the dive should be slow to avoid decompression sickness.

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