Why Do Planes Fly So High?

The reason aeroplanes fly so high is due to improved fuel efficiency. A jet engine operates more efficiently at higher altitude where the air is much thinner, allowing an aircraft to travel faster whilst at the same time, burning less fuel.

What happens if a plane flies too high?

When the plane gets too high, there is insufficient oxygen to fuel the engines. "The air is less dense at altitude, so the engine can suck in less and less air per second as it goes higher and at some point the engine can no longer develop sufficient power to climb." ...

Why do planes fly at 35000 feet?

A balance between operating costs and fuel efficiency is achieved somewhere around 35,000 feet, which is why commercial airplanes usually fly at that altitude. Commercial airplanes can climb to 42,000 feet, but going beyond that can be precarious, as the air starts to become too thin for optimum flight of the airplane.