From: Mxsmanic
Date: 11/2/2003 6:56 AM Central Standard Time

Beyond a certain altitude (usually from
30,000-90,000 feet, depending on the aircraft), there isn't enough air
to maintain lift and/or power the engines, and so you can't go any
higher than that, which prevents
That is why the GLIDER altitude record is just a tad under 50,000 feet.
Never got over 18,300 feet myself. Mac