Yesterday, some of us in the F/B group were reading Lex’s post on hypoxia. It reminded me of a time in the early 80s as a (then) active pilot with the massive experience of 200 hours, I was given the opportunity by the FAA to attend the Navy’s physiological course at (then) NAS Miramar. It was probably the same place Lex went to a few years later.
That day remains etched in my mind for all that I learned. As I recall all those years ago, it was comprised of 2 parts – the causes of vertigo and hypoxia, which is the body’s reaction to the thinning air at altitude.
Both can be insidious and sneak up on you, and you aren’t even aware of it. Both can kill you if you are unaware of their effects.
Lex gave a perfect example in his post when he unknowingly had a crack in his O2 mask and was becoming hypoxic. It took his instructor pilot to recognize it. A lot of times as you learned in that altitude chamber, you can feel no physical symptoms. The only clue is a mental dullness. Which is easier to be recognized by others than yourself. And if you keep climbing, unconsciousness.
Once at altitude, the O2 bleeding past the crack in my mask became an issue, and it became clear watching the usage rates that we would not have enough O2 to carry us all the way to the west coast. We couldn’t descend to a lower altitude, since the fuel utilization would rise unacceptably, there were no acceptable diverts between us and San Diego, and so we had to remain at altitude.
My instructor came up with a bright idea: we would take turns on the oxygen. When one of us got to feeling hypoxic, he’d put the mask on, and the other would take his off. In this fashion, we’d make it safely all the way.
What could possibly go wrong?
We’d been airborne for a bit more than an hour or so, and I’m off the O2, feeling fine. Feeling really good, in fact. WHEE! But there’s a buzzing in my cheeks, my head feels funny, and the colors are starting to grow a little dim. S’OK, though – probably because it’s dark outside!
My instructor asks me to figure out our remaining time to San Diego, as well as our fuel on deck upon arrival. I did some back of the envelope math, and came up with, “Two and a half hours, and we’ll have 5000 pounds of gas on arrival.” There was a long, pregnant pause from the front seat. Problem was, we’d been airborne for an hour and fifteen minutes, and the longest we could have stayed aloft was about 2.5 hours. I’d just calculated a time on deck that was 75 minutes longer than we’d have gas. Oh, and by the way, the T-2 carried about 4000 pounds total. My hypoxic math had just magically transferred another 1000 pounds over capacity into the aircraft, after we’d already used up about 2000 pounds.
At Miramar, our instructor played a 12 minute recording between ATC and an F4 pilot. The pilot unknowingly had no oxygen through his mask and during his climb within a few minutes was asking the controllers to repeat the instructions – as he continued to climb he became more incoherent. If I remember the recording he became unconscious and crashed at 12 minutes.
Hypoxia is what killed PGA pro Payne Stewart and crew in his chartered Learjet. Either the pressurization system never worked during the flight, or it failed at some point during its climb. An F-16 sent by ATC followed its eerie silent flight on autopilot until it ran out of fuel over South Dakota.
That is why when the airline flight attendants explain that if the cabin pressure is lost and the O2 masks drop, put yours on first then help others. An airliner is generally pressurized to about 8,000 feet. Still pretty thin air, but you aren’t running a marathon so you don’t notice it. Unless it’s a Boeing 787 Dreamliner where, because of its composite construction, it is about 6,000 feet. The thicker air during long flights is supposed to make one feel more rested at the destination.
That thin air can affect not only your body, but your airplane. Every now and then there is an accident at Lake Tahoe’s airport in the summer. It will be hot for 6,000 feet – 90 degrees – even 100. You load your plane with passengers and baggage and begin your takeoff.
Only the plane seems to take a lot longer to lift off. And when it does, if it does, it takes a lot longer to climb.
Fortunately all of these passengers survived, but this is a video demonstrating those conditions. But notice how slowly it is on the runway to liftoff and how it barely climbs:
On a good summer day back at Tahoe, if it is 90 degrees (which is common), the true elevation may be 6264′, but as far as the plane is concerned with the density altitude, it is really at 9,900′. The heat makes the air molecules all that more dispersed, with fewer flowing around the wings.
How much runway does your plane need at 9,900′, and how fast can it climb?
Even airliner pilots at places like Quito, Ecuador (elevation 9,350′) , pay attention to the density altitude.
What I thought was equally interesting was their demonstration of vertigo. There is no more helpless a feeling when you are in control of a plane and your head feels like it is spinning. Happened to me once when I was flying alone. It can and does kill pilots, particularly ones who are not instrument rated and go into instrument conditions (that wasn’t my case).
That was the cause of John Kennedy’s accident off Martha’s Vineyard.
You have to absolutely trust what your instruments are telling you and not what your body is “telling” you.
Vertigo starts in the middle ear.
To demonstrate this at Miramar, they led us to a darkened room with a chair not unlike a barber’s chair. You’d be blindfolded, and they would spin you at various speeds. You’d never go really fast, but varying speeds. What this was doing was moving the fluid in that middle ear.
They’d ask you when it has stopped.
Most of the time you’d think you had stopped when you hadn’t, or thought you were still moving when you had stopped.
Good pilots are aware of their surroundings, and more than one flight as been averted until the morning when it is much cooler.
Situational Awareness is more than just being aware of your surroundings in flight.