7 or 8 years ago I read an article in an Aerospatiale Mag. about a pilot in the Nepalese Army flying a Squirrel not sure what type, would have to be a B2 or similar, made a landing in the Himalayas at around the 20 000ft mark on two occasions to affect a rescue.
I don't have the article, but he was a well known pilot for his previous rescues in that area and it was the highest landing he ever did. Perhaps some other ppruners will have the details.