The Payne Stewart Intercept - A Startling Reality

[Par]

I'm under the impression that above 40,000 ft, w/o oxygen you have surprisingly little time before passing out. I believe I read at the time of the Payne Stewart crash, perhaps only 15-20 seconds. Confirmation anyone?

If it helps, and if I recall correctly, you’d have around twelve to fifteen seconds of useful consciousness available to you were you to be subjected to an explosive decompression in deep space.

 

[gumboot]

I'm under the impression that above 40,000 ft, w/o oxygen you have surprisingly little time before passing out. I believe I read at the time of the Payne Stewart crash, perhaps only 15-20 seconds. Confirmation anyone?

Here's a useful chart.

Time of Useful Consciousness (time in which efficient flying duties can be performed) at 40,000ft is 15 to 20 seconds. N47BA was climbing from FL 230 (23,000ft) to FL 390 (39,000ft) when communication was lost.

 

[Reheat]

Time of Useful Consciousness (time in which efficient flying duties can be performed) at 40,000ft is 15 to 20 seconds. N47BA was climbing from FL 230 (23,000ft) to FL 390 (39,000ft) when communication was lost.

Yep, these are good numbers based upon my experience. They likely had a slow insidious loss of pressure as they climbed perhaps extending their TUC by a few seconds. Had it been an explosive decompression they likely would have noticed it.

As it was the crew had no practical training in high altitude hazards and likely didn't realize what was happening, in addition to not checking the gauges.

Unfortunately, because it is so expensive and only a few altitude chambers exist, usually only military pilots receive actual insidious or explosive decompression training.

 

[BenBurch]

My father had to take chamber rides with UAL, but his was likely a special case as he had emphysema and they needed to make sure he could function at 10K and for long enough to get his mask on in a decompression. Eventually he didn't pass and they cashiered him.

 

[gumboot]

Yep, these are good numbers based upon my experience. They likely had a slow insidious loss of pressure as they climbed perhaps extending their TUC by a few seconds. Had it been an explosive decompression they likely would have noticed it.

As it was the crew had no practical training in high altitude hazards and likely didn't realize what was happening, in addition to not checking the gauges.

Unfortunately, because it is so expensive and only a few altitude chambers exist, usually only military pilots receive actual insidious or explosive decompression training.

The only issue with the slow decompression idea is that the aural warning was functioning correctly so if a slow decompression was occurring they should have got plenty of warning. An explosive decompression, in contrast can halve the the TUC. According to ATC tapes there was no sound of the aural warning when they last communicated with ATC, and only 6 minutes later they weren't responding at all.

 

[DGM]

The only issue with the slow decompression idea is that the aural warning was functioning correctly so if a slow decompression was occurring they should have got plenty of warning. An explosive decompression, in contrast can halve the the TUC. According to ATC tapes there was no sound of the aural warning when they last communicated with ATC, and only 6 minutes later they weren't responding at all.

If memory serves (doesn't always). When the plane was intercepted the windows were "fogged". Wouldn't that suggest a more sudden decompression? Just asking questions.

 

[bonkey]

So "they" knew there were problems with scrambling jets before 9-11

There was no problem. The system worked exactly as designed.

It is only with the hindsight of 911, and the requirements for the same system to cater for a problem it wasn't designed to handle that a failing becomes obvious.

 

[soylent]

What's the difference between "owned" and "pwned?"

About 10 IQ points.

 

[Reheat]

If memory serves (doesn't always). When the plane was intercepted the windows were "fogged". Wouldn't that suggest a more sudden decompression? Just asking questions.

Nah, the result would be the same either way. It would be more rapid with an explosive decompression, but the result noted would also have occurred by the time a fighter got close enough to observe the fogged windows and windscreen.

It surely will remain a mystery as gumboot has pointed out, apparently the aural warning was working.

If there had been an explosive decompression they should have begun an immediate rapid descent while they analyzed the problem. That would be considered "common sense" by any pilot engaging in high altitude flying. Since they didn't it would be reasonable to assume it was insidious and somehow the problem went unnoticed.

 

[BenBurch]

Sometimes people hear a warning and spend the first few seconds finding out why the warning is sounding when it should not. And then possibly deciding that its a fault and not a real warning. It all comes to training.

 

[gumboot]

If there had been an explosive decompression they should have begun an immediate rapid descent while they analyzed the problem. That would be considered "common sense" by any pilot engaging in high altitude flying. Since they didn't it would be reasonable to assume it was insidious and somehow the problem went unnoticed.

Having said that, according to the TUC chart in an explosive decompression at those altitudes they could have had as little as 7 seconds before they passed out. N47BA's flight was punctuated by quite extreme changes in altitude, but the heading never varied which to me suggests a pilot was lying lifelessly on the control column. It seems at least possible that they started a rapid descent but passed out before reaching a safe altitude or getting their oxygen masks on, then could have slumped backward, pulling the control column back and sending them back up. Or something like that.

We'll never really know, because the CVR only records 30 minutes.