SR-71 Altitude Story

Some background first. FL600 is 60,000 feet, the altitude at which Air Traffic Control is no longer in charge, if you can climb above that point you're on your own. A modern airliner (777 for example) cruises at FL450 and isn't super happy to fly above that.

• SR71: QQ requesting clearance to flight level 600
• ATC: QQ, climb and maintain flight level 600... if you can get there.
• SR71: Roger, descending to flight level 600 from 850.
• ATC: Uh... roger