Expert: Mark Janus - 2/3/2011

Question
Sir,I just want to know that why the aircrafts cannot fly above a certain altitude like for example F-16 can fly upto 56,000 feet,mig-25 can reach upto 75,000 feet but not above that altitude.
Why can't these planes fly above 75,000 feet altitude.
Please help
Thank you

Answer
The air is to "thin" at extremely high altitudes...  Basically the air molecules settle near the Earth's surface (via gravity)...  so the atmosphere varies in air density more at sea level and less at high altitudes...  think about mountain climbers (even at 11000 feet the air is thin)...

That's why there is a service ceiling on aircraft (some do better than others at performing at high altitudes)...

Thanx,
mj