Besides the Air Traffic Controller (ATC) Nightmare There are a number of reasons to mention.
Planes need speed through the air to create their ‘ lift ‘.The higher you come into the atmosphere, the more thinner (thinner) the air. This means you have to fly harder to generate the same lift at the same angle of the air against the wing.
When the air becomes more icy, not only does the lift take off, but the engine power as well.The air resistance also decreases with the height. There is a moment when an airplane cannot climb higher, because the power that can still be delivered is not enough to go even faster. Then you can no longer create an extra lift to fly even higher, despite the fact that the air resistance decreases at even greater altitude.
An airplane engine is almost always a compromise.Engines that are efficient at very high altitude (straight-jets or ram-jets) are very inefficient at lower altitude and lower speeds and can often provide less power for takeoff.
You will often see large engines with a relatively small jet engine on passenger planes.This is called the ‘ core engine ‘. The jet engine delivers the power to the fan that nowadays delivers 80 -90% of the thrust and the real jet engine is only 10 -20%. This is what you call a turbofan. These motors can deliver very much thrust at low altitude for takeoff and climbing, but are relatively inefficient at very high altitude (still much more efficient at high altitude than at low altitude). Straight-jets (mostly old type jet engines) are precisely at very high altitude more efficient than turbofans, but very inefficient at lower altitudes.
What speed is also a factor in passenger planes is the speed of sound.Engines cannot be made much bigger, because the fan blades can easily pass through the sound barrier to the tips. This can also be heard around Schiphol Airport, because then the engines are going a bit round. This is not so bad for the engine, but it does at the expense of efficiency. During takeoff and the climb that is fine, but should not occur in the Cruising Flight (cruise). The higher you get into the atmosphere, the lower the sound speed.
When planes fly extremely high they cannot fly much harder, because then they approach the sound speed (very dangerous for planes that are not designed to do this) and if they go a little slower, the wings and lose the Largest part of the lift.
If one is said by some, yo-yo-and through the air this results in total seen more fuel consumption than when one simply stays with the engine at height.Compare this with your car on the highway if you release gas at 150, then in its free move to 70 km/h and then again it should accelerate to 150 to repeat this all the time. This does not result in a saving! Even if you would turn the engine off during deceleration.
Once an airplane has the ability to leave the vapor circuit at a speed that is high enough to get (almost) into a low-orbit then we are talking about a different kind of flight.For short distances this would be absurd and very inefficient, but for very long distances as from Amsterdam to Asia or even further it would cost less fuel and could shorten the travel time with perhaps 90% or more. Developments in this direction have been going on for a while, but it will take some time before we start seeing this in practice.
Is there still the introduction of water vapour in the higher air layers of the atmosphere where naturally much less water occurs (above the tropopause occur as good as no clouds) may have very undesirable consequences on the climate as We flock through space to fly.Water is a lot of are greenhouse gas than CO2.
To be able to lay the desired distances you would have to fly either enormously high at once before moving into the ‘ float ‘, or going up a number of times, floating down and going high again.So no fuel savings would occur. In addition, there are few engines that can reach the enormous heights.
Passenger planes are also not designed to really be able to float.The ‘ Yo-yo’en ‘ would cause more damage to the construction of the aircraft, and also not be as enjoyable for the passengers.
Planes and engines should be redesigned, and the whole would be a nightmare for Air Traffic Control..