Why can’t a jet fly higher than about 15 km?

Question

Why can’t a jet fly higher than about 15 km?

Answer 1

Some of them can, it depends on the design.

However, as a general rule the answers above about air density and lack of enough  oxygen are correct.

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Answer 2

jets in general, ie: aircraft with turbine engines CAN fly higher than 15km. its just that they become less efficient at higher altitudes. obviously, they cannot fly too high (more like 20km) because there is not enough air at that height. even though jet engines compress the air first, unless they were developed to fly at 50,000+ feet, they aren't really good at that altitude.

commercial aircraft cannot fly higher than 43-45K feet because of pressure differences. the cabin is pressurized to the atmospheric pressure of that found at 8000 feet. which is what the average person can withstand without trouble,

the higher you go, the bigger the difference in pressure you get. there will be a point where the fuselage will fail and explosive decompression will result. so commercial airliners don't go higher than 45k feet to keep structural integrity for as long as possible.

Answer 3

The reason why some jets have height restrictions are clearly sturctural. The plane has to be able to keep the presurization at about 8000 ft AGL. This means that the higher the plane goes the more pressure there is acting on the outside of the plane. The lack of oxygen at higher altitudes is also a problem.

Answer 4

15km is over 45,000ft. The air is too thin. The propulsion system for a jet depends on air mixing with the fuel and burning when a spark or flame is introduced to the mixture.

Too high and there is not enough oxygen to sustain the burn.

Answer 5

concorde was able to fly at around 56,000 feet, which is above 15km, so it is possible, but very expensive to develop.

concorde was amazing as it was designed nearly 50 years ago and nothing has replaced it, an interesting fact is that fighter jets could not fly at supersonic speed for much more than an hour, and the pilots needed G suits, in concorde 100 passengers could enjoy champagne and caviar !!

Answer 6

Jet engines or turbo fan engines require oxygen which mixes with the jet fuel and is ignited to create thrust.  The diminished oxygen at higher altitude means that the the air/fuel mixture is less oxygen rich which can significantly lower thrust, therefore the jet can not safely operate.

Answer 7

all planes need a smooth airflow over the wings to fly,this is achieved by going through the air above a required speed.

the higher up you go the thinner the air gets, so more air flow is required over the wings to keep the plane air born, but the normal turbine engine cannot produce enough thrust to move the plane through the air to keep the plane air born

Answer 8

the main reason is that the engine needs o2 to burn its fuel there is not enough at high altitude a rocket engine normally carries its own propellants

Answer 9

We pilots sure know how to complicate our answers huh. Many fly higher than 15 km.