You’re in the right place if you’ve ever wondered how high airplanes fly and why they must maintain cruising altitude!
You may barely notice the routine stages of flight if you’re a frequent flier. During the first 15 to 20 minutes of the flight, the airplane climbs. As soon as the plane reaches cruising altitude, flight attendants start making their rounds, and the pilot may announce that you are free to move around (though you must keep your phone on airplane mode).
As soon as the descent begins, fasten your seatbelts in preparation for landing. The airplane cruises at a steady altitude between ascent and descent. Is there a limit to how high planes can fly? What is the purpose of keeping them at a certain altitude? If you’ve ever asked yourself these questions during those long hours spent staring out that round window, here’s the answer!
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How high do planes fly?
A commercial aircraft’s cruising altitude depends on its size. As a general rule, commercial passenger jets cruise between 32,000 and 40,000 feet, or six to seven and a half miles above the ground.
In comparison to larger aircraft, turboprop planes fly at a lower altitude of about 25,000 to 30,000 feet, carrying a handful of passengers rather than hundreds. As propeller planes are often used for short-haul flights, they may stick to lower altitudes because once they reach a higher altitude, it is time to descend.
What happens if an airplane flies too high?
Do you remember Icarus, the Greek mythological character who perished when his wings melted when he flew too close to the sun? Passenger planes are not at risk of melting if they fly too high, but cabin pressure and oxygen concerns require them to stay below set altitudes. An Airbus A-320/321 captain and retired USAF F-15 pilot, Theodore Kyrazis, explains it this way:
- Emergency oxygen supply: Kyrazis says airlines impose altitude limits, “to ensure there is enough oxygen available to all masks for the duration of the descent to an altitude where masks are no longer needed (almost 10,000 feet).”
- A sudden cabin depressurization can occur if a plane flies too high, causing passengers and crew-including pilots-to lose consciousness. Whenever this happens to a fighter jet, Kyrazis explains, “it’s as simple as rolling over and going straight down to a comfortable altitude in less than a minute.” Commercial aircraft don’t have this luxury.”
- Modern aircraft have sophisticated computers that monitor weight, speed, outside air temperature, wind speed and direction, and the angle of the wing to the incoming wind,” Kyrazis says. “If a pilot climbed above the recommended altitude and kept going, either the engines would not produce enough thrust or the wings would stall.”
What’s the bottom line? The recommended altitude should be followed by your pilot!
Other reasons planes fly at cruising altitude
In order to make money, commercial airlines need to operate efficiently and not just by charging for in-flight WiFi. The fuel economy of planes is one of the most important factors in their altitude. A turbojet engine burns less fuel as the density of the air decreases, according to Kyrazis.
There are some fancy calculations involved, but essentially, the speed and angle of degrees at which the plane climbs are determined both by weather conditions and by the size of the plane; larger planes weigh more, partly because they carry so much heavy fuel, which burns off as they climb.
Kyrazis estimates that one hour of climbing burns off 10,000 pounds of fuel. One gallon of gas saved on each flight for a year would save a major airline more than $15 million! ”
In general, the higher a plane flies, the faster it can fly. “Thanks to less dense air at higher altitudes, the actual speed the aircraft is traveling over the ground is much faster than the aircraft speed indicator shows,” says Kyrazis.
That means the plane is making better time than the instruments indicate. However, extremely cold temperatures will slow the plane down. In order to balance that out, pilots find that happy medium between fuel-saving high altitudes and the slowing effects of subzero temperatures. This isn’t why airplanes are so cold.
On a flight, nobody wants to experience turbulence, but it’s more likely to occur during ascent and descent. According to Kyrazis, much of the turbulence associated with weather systems can be avoided above 35,000 feet, which is why commercial aircraft like to climb above storms.
Except for thunderstorms, which can reach 50,000 feet into the atmosphere, he says. A plane must either go through or around the storm when that happens.
What happens if a plane flies too low?
Despite all the frightening things that can happen when a plane flies too high, flying too low can be just as dangerous. In addition to flying through bad weather systems at lower altitudes, there’s a lot more general aviation traffic at lower altitudes, including smaller commercial and private aircraft.
Is there another big risk associated with flying at low altitudes? Birds getting in the way. According to Kyrazis, most bird strikes occur during takeoff and landing. This includes the 2009 “Miracle on the Hudson” and Captain “Sully” Sullenberger’s heroic landing. Birds and planes are less likely to encounter each other at an altitude of 10,000 feet or higher.