Different types of aircraft can fly at different heights and this largely depends on whether they are pressurized; the type of engines they have and their role (leisure, business, commercial or military).
Commercial aircraft today fly at altitudes up to 42,000 feet (which is just under 8 miles high). Concorde used to fly at altitudes up to 60,000 feet (over 11 miles high) and at that height you could see the curvature of the Earth. Some military aircraft (the SR-71 Blackbird) could fly up to 85,000 feet.
This article will show how high airplanes fly for various groups of aircraft.
How high do commercial airplanes fly?
Most commercial airplanes have a cruising altitude between 30,000 feet and 42,000 feet, with an average of around 36,000 feet. The maximum altitude passenger jets fly has increased over the years as engines have developed to become more powerful which allows them to fly at higher altitudes.
Concorde had a very high operating altitude of 60,000 feet. This was mainly possible due to its very powerful Rolls Royce Olympus engines. At such a high altitude the air was thinner so there was less drag which enabled it to fly faster at more than twice the speed of sound (1341 mph). You could also see the curvature of the earth at that altitude.
In the days of commercial airplanes with piston engines, back in the late 1940s and the 1950s, aircraft couldn’t fly as high as today since piston engines were less highly powered and would not work efficiently at altitudes of 30,000 and above.
Some piston-engined bombers were able to fly at almost jet airliner altitudes. For example, the B-17 Flying Fortress could fly at just over 35,000 feet but this wasn’t for reasons of fuel efficiency but because it made them safer from fighter aircraft and ground-based guns.
How high do private jets fly?
Private business jets often fly higher than commercial jets as they generally have a higher power to weight ratio which allows them to cruise at higher altitudes.
The Gulfstream G650 for example can fly up to 51,000 feet.
How high do fighter jets fly?
Fighter jets can fly at quite high altitudes, often around 50,000 feet. This is due to them normally being aerodynamically very efficient and to having powerful jet engines which give them a high power to weight ratio.
Fighter jets are built to perform different roles such as ground attack, air to air combat or even multi-role, so their operating altitude may vary depending upon their role.
The highest flying military aircraft
The military aircraft that flew the highest (and the fastest) was the Lockheed SR-71 Blackbird which was developed in the 1960s as a reconnaissance aircraft for the USAF.
It could fly at altitudes of over 85,000 feet and at speeds in excess of 2200 mph, which is greater than three times the speed of sound (Mach 3).
Why do airplanes fly so high?
There are a number of reasons why airplanes fly high, rather than at lower altitudes.
Less air resistance
How high planes fly is mainly due to the higher an airplane flies the less dense the air becomes (ie. thin air). The thin air creates less air resistance (known as drag) on the airframe of the aircraft at a higher altitude so the faster it can fly.
At higher altitudes, due to the lower air density, the less fuel the engines need to propel the aircraft along at a certain speed. That is important to commercial airlines.
In addition, the temperature at high altitudes is lower, and generally, the lower the temperature the more efficiently a jet engine runs.
Above the weather
Flying at altitudes of up to 42,000 feet means that the airplanes are normally flying above the weather systems where the air is more stable so the flight will be more comfortable for passengers.
How high do light planes fly?
Most light private aircraft normally fly between 2,000 feet and 6,000 feet although they would often be capable of climbing higher to altitudes of 14,000-15,000 feet. For example, the popular Cessna 172 has a maximum ceiling (altitude) of 13,5000 feet.
Why do light private aircraft fly lower?
Light private aircraft are limited as far as the altitude they can fly because:
They are not pressurized
Light aircraft are normally not pressurized, so unless the aircraft was fitted with an oxygen system, pilots might suffer from a lack of oxygen if flying above 15,000 feet.
Most light aircraft’s engines are generally not very powerful so have a limited maximum ceiling height.
They make short flights
Generally, light aircraft are used to travel relatively locally so even if they could, climbing to a high altitude would not make sense
Air traffic control restrictions
Light private aircraft can be restricted to flying at lower altitudes by airspace regulations and also by the competence/licensing of the pilot. Many private pilots (such as myself) are not trained to fly on instruments alone so need to fly within good view of the ground (under VFR – Visual Flight Rules).
How do pilots decide what height to fly at?
The gross weight of the aircraft (including the empty aircraft, crew, passengers, baggage, cargo and fuel) will largely determine the best cruising altitude for the aircraft to fly at. However, after that, a few other factors come into play.
The air traffic control room (ATC) will ultimately have the final say in what altitude an aircraft will fly at. A pilot may request ATC to give them a different altitude, perhaps to avoid a weather front or just to fly more efficiently, but it is up to them if that request is granted, based on traffic congestion etc.
In much of the world, particularly in busy airspace, aircraft always fly along airways. Airways are basically the invisible highways in the air that make up the air traffic control network.
In a road network, which is basically two-dimensional, one lane (or lanes) travel in one direction and another lane (or lanes) travel in the opposite direction, next to each other.
In an airway, which is in three dimensions, lanes are stacked one on top of another, with odd-numbered altitudes (eg 31,000, 33,000, 35,000 feet etc) traveling in one direction and even-numbered altitudes (eg 30,000, 32,000, 34,000 feet etc) traveling the opposite way.
An air traffic controller will allocate which altitude an aircraft will fly at (either odd number or even number of thousands of fee) based on its direction of travel along the airway.
How high is space?
As aircraft continue to fly higher and higher it may be interesting to know whether they are reaching altitudes that might be considered being in space. But they have a long way to go yet.
How high is space depends on which organization is defining it. The US generally defines it as starting at an altitude of 264,000 feet (50 miles) but internationally it is normally regarded as starting at 380,000 feet (62 miles) which is also known as the Kármán line.
So even the highest flying military aircraft are still a long way from being in space.