Why do airplanes fly at such a high altitude? 50,000' right? why not 20,000, 10,000?

Question

Is there an advantage as far as avoiding wind patterns or is it more economical to fly higher in the atmosphere?

Answer 1

Part of the reason they fly that high is because it helps fuel efficiency. Turbofans, (jet engines), normally operate at high temperatures, so the higher you fly the cooler the engine runs and more power is available. There is a catch though. High altitude also means "thinner", or air poor in oxygen, tranlating to higher engine RPM requirements  Luckily, turbofans also operate comfortably at high speeds, (referred to as Ng).

Answer 2

to fly about 30K feet above ground versus 20K means you would cover more nautical miles (miles relating to the roundness of the earth).

Answer 3

2 reasons one weather two what would happen if you were to loose an engine or two etc you would want to be the highest you can there are a few little reasons such as noise reduction less fuel burn and clearer airspace for GA

Answer 4

Less Traffic (not as many planes can fly up there)  Less Air Resistance (air is thinner=less drag=better fuel economy)

Answer 5

It is mostly the high end business jets that reach those altitudes, most airliners don't go over 40,000.

Answer 6

First to get above the WX, Second to take advantage of favorable winds, Third fuel economy.

Normally Airlines fly in the low to upper 30,000 ft area (33 to 39,000) But FL 410 is not uncommon

Answer 7

There are different altitudes for different applications. Airliners fly so high because it is economical. Other planes like military have their own air space to play in although they can fly anywhere with a flight plan. Same with general aviation. There is also a method of assigning altitudes such as those flying North fly and an odd height and those going South fly at an even altitude (just an example).

Answer 8

Weather avoidance, wind, and fuel economy.

Answer 9

You won't find them at 50,000'. Most fly at 30 to 36,000'. The winds aloft and fuel consumption due to less drag in the thinner air are the main reasons.

Answer 10

50,000 or FL 500 is a bit high for commercial aircraft.  The only aircraft you see at that altitude on a regular basis is military aircraft.

The reason they fly between 18,000 MSL (FL180) and  60,000 MSL (FL 600) is because this is class A airspace.  That means they will be on a required IFR flight plan regardless of weather conditions.  This gives them the safety advantage of being in positive control by an ATC facility.  An ARTCC (Enroute Area Control Center) will provide positive control at all times and coordinate handing them off to other ATC facilities including approach control, when they reach their destination airport.  They also provide radar separation for all aircraft in class A airspace.  So safety and easy navigation is on factor.

The other is performance.  Both jet and turbojet aircraft preform better at these altitudes.  Fuel consumption being the primary concern.  Also the jet stream can if at the right altitude and in their favor reduce flight time considerable.

This is a simplified explanation for more info look at the link below.

Hope that helps :-)

  http://en.wikipedia.org/wiki/ARTCC

Added: What all the ATP pilots are saying about performance is a lot more acurate info than I could give.  All my time was in single engine prop.

I am also disapointed, all this time I thought you guys filed IFR flight plans just because you liked talking to us ATC types.  :-)

Answer 11

They fly high enough to avoid bad weather; clouds etc.

Answer 12

You have to fly at 30,000ft or higher in order to avoid most bad weather or winds.  Trans-Atlantic or Pacific flights go higher because it's actually a shorter path at higher altitudes.

Answer 13

The thinner air makes it more economical to fly there, also the worst of the bad weather can be avoided! Although I don't think that they fly as 50,000 feet as the air can be to thin for the engines to work and the cabin pressure would be hard to maintain at the altitude!

Answer 14

I like all these answrrs, my only addition is to expand on the economy issue, because the air is thinner, you can achieve the same fuel ratio by injecting LESS fuel, which increases economy. When you fly lower the air is denser, so you need MORE fuel to have the proper ratio.

Answer 15

Airliners go up high to reduce fuel burn and to increase there "true airspeed" If you could go up front in an Airliner and look at the airspeed indicator you would be shocked to only see 250 to 280 knots ( depending on altitude ) on the airspeed indicator. But you are really probably doing 400 to 480 Knots, 460 to 552 MPH. How that works is, we basically live at the bottom of the ocean of air. Air has mass/weight at sea level we are under 14.7 pounds per square inch ( I think, other pilots please cut me slack if I am not exact ). At 18,000 feet there is half that pressure. Therefore less molecules of mass (air) per square foot for the aircraft to push through, which equals less resistance. But with less air to push through there is also less air for the engine’s, be it piston or turboprop or Jet. Piston engines they make less power the higher they go, unless they are turbocharged then they can go much higher than a normally asperated piston engine. A turboprop is a small turbine engine ( jet ) transferring most of its power through a gearbox out to a propeller providing the thrust. Being turbine powered it can make massive amounts of power down low in the thick dense air. To keep from damaging components of the engine and gearbox they impose limits on it but as you go higher you can see the power dropping off due to a decrease in air density. So therefore as you climb you can give it that extra power. So as you go higher you can make allot of power up to a higher altitude. Which means lots off power up high = a high indicated airspeed up in the thin air which = a higher true airspeed = Goes fast!

Pure jets fall under this same explanation, Reserve power for high altitude.

Fuel economy

The new airliners do get above FL400 all the time on long trips. FL 470 is about the highest that is used on a normal basis by biz jets.

Answer 16

only jet aircraft designed to fly that height to prevent ultra sonic effects