On Sunday, December 23, 2018 at 9:59:15 PM UTC-8, wrote:
I would like to correct a couple of statements made here with respect Bob Harris’s altitude record flight. My apologies for being slow to respond.
1) Bob Harris did not limit his climb “because he couldn't keep his mask on”. He terminated the climb because he believed one of his two oxygen systems had malfunctioned.
2) However, the statement that he was “forced down when his oxygen system started to fail” is also incorrect. His subsequent investigation showed that both oxygen systems were operating within specification. The problem was they were not operating identically. As Bob pointed out in his presentation to the World Gliding Championship at Benalla, Australia the following year, differences in the regulators’ pressure settings, stiction between the components, the lack of vibration in the sailplane to address that stiction and the fact that the regulators were at or near their operating limit, resulted in a substantial difference in the pressure he felt in his mask when he switched between the two systems. He interpreted this difference as an indication that one of the two had failed, but later determined it had not.
3) He did not suffer from any medical condition as a result of his record flight.
Mike Koerner

Thanks Mike. After reviewing Bob Harris's article I have a few observations:
1) the regulators he used we MD-2s not A-14s. These were manufactured by Cobham Life Support.
MD-2 regulators are obsolete; they were the 2894 series and they got replaced by 29255 series regulators. Very similar units. No idea how these compare to A-14s except they were both rated to ~50k'.

2) the account I heard, but did not verify, was that Bob terminated his flight because he couldn't keep his mask on (due to high pressure on the mask).. You note, and the article confirms, that he reported what he thought was a failed regulator (delivering higher pressure than expected). Is it possible that these reports are related i.e. the regulator he thought had failed was delivering higher pressure than the other one - and so it as forcing his mask off? Maybe a minor point but maybe not. At some point, if the mask is not tight enough it may be forced off and this is something to be prepared for. I added an extra strap on my mask as a backup to the 8 snap connections on my A-11 helmet for this reason.

3) I had heard, but did not confirm, that he vented his mask to the outside but in his article he clearly states he frosted up above 32,000' and was flying on instruments by 39,000' has he had zero visibility! I also experienced significant canopy icing on both my flights to 25k' and 28k'. I was able to "scrape and wipe" to maintain visibility but I expect this could be an overwhelming task at 30k' and above. I am looking at ways to apply film "windows" on both sides of my canopy and also vent my exhaled air to the outside. This is another significant issue to address.

Appreciate your feedback. It's obvious that lot's can go wrong attempting these high flights and the more accurate info we can learn from the better prepared we can be.

I also fly with an oximeter and have found the readings to be very informative for evaluating cannula versus mask performance. However, it would appear that even these can be misleading, if I recall the recent SSA article correctly, so again, good to know and more work to be done.

Jim
VVII