about 42k ft
Commercial, jet engined aircraft, such as the 747, fly at approximately 40 000 feet. Propeller aircraft fly at lower altitudes
To fly a jet for non-commercial use, first you must obtain a Private Pilot's license. Then you must be certified on each individual aircraft type you wish to fly. To become a commercial pilot, you must then complete the training and hours requirements to be certified as a Commercial Pilot. Again, you must be individually certified or "rated" for each different aircraft you fly.
Up to 41,000 feet, like most other large jet aircraft.
varies on aircraft size
An aircraft that cannot fly.
The first turbojet aircraft to fly was the Heinkel He 178
It depends on what kind of jet or commercial airplane it is.
Commercial aircraft fly at 25,000 to 35,000 feet, where the air is thin enough to reduce air friction and where atmospheric weather turbulence is less. The higher altitudes do not provide sufficient lift and there is less oxygen for the jet engines. Supersonic aircraft such as the Concorde and Tu-144 operated at even higher levels (up to 65,000 feet) because of the heating caused by very high flight speeds.
The Comet
The Harrier Jump Jet
These days passenger jet aircraft are the norm
Most commercial jetliners fly routes between 28,000 and 35,000 feet.