All sorts of very tender stuff freezes at 18K ft, that's what's wrong. Or even 17,999. Ask me how I know.

Lynn Alley
"2KA"

PS. I once froze my wife on a high-altitude flight in the late fall, and had to try to hold her tight with my whole body post-flight to keep her from going completely hypothermic. I thought it was very romantic. She did not.