Why do planes burn more fuel at higher altitudes?

Air density decreases with altitude, thus lowering drag, assuming the aircraft maintains a constant equivalent airspeed. However, air pressure and temperature both decrease with altitude, causing the maximum power or thrust of aircraft engines to reduce.



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The reason planes cruise at high altitudes is that they burn less fuel and can fly faster, as the air is less dense. At 30,000 feet and higher, it is also possible for aircraft to avoid weather systems, making it more comfortable onboard.

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When an airplane experiences less drag, it consumes less fuel. This relationship between speed and fuel consumption means that flying at a slightly slower speed can result in significant fuel savings for airlines, which in turn can lower operating costs and potentially reduce ticket prices for passengers.

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In the event of an emergency requiring a return to the departure airport, the aircraft circles nearby in order to consume fuel to get down to within the maximum structural landing weight limit, or, if the situation demands, simply land overweight without delay.

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Fuel dumping (or a fuel jettison) is a procedure used by aircraft in certain emergency situations before a return to the airport shortly after takeoff, or before landing short of the intended destination (emergency landing) to reduce the aircraft's weight.

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Because the Earth is a three-dimensional sphere and not merely a two-dimensional flat, East-West surface. Because of this spherical shape, often times the shortest distance is flying more north and south, up over the Northern latitudes and the North Pole, rather than flying east/west over the Pacific.

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Whether flying at night or during the day, pilots need to see some kind of horizon. They use this to determine the airplane's attitude. At night pilots will turn their gaze from outside to inside and use the artificial horizon. The artificial horizon is normally a simply globe split into two hemispheres.

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If the aircraft tried to land without dumping the fuel first, it is considered an overweight landing attempt and could place immense stress on the airframe. It could also increase the risk of fire and fuel leaking onto the tarmac.

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Simply add the strength of the headwind (30 mph) to your best glide speed (78 mph) and you've got the most efficient speed to fly—here, 108 mph. To determine an airplane's Carson speed, multiply its best glide speed by 1.32. This will get the best result in terms of true airspeed and fuel consumption.

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Commercial airliners, such as the Boeing 747 and the Airbus A380, have a range of around 8,000 to 8,500 nautical miles. This means that they can fly for up to 20 hours without refueling, allowing them to travel long distances across the globe.

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Typical takeoff air speeds for jetliners are in the range of 240–285 km/h (130–154 kn; 149–177 mph). Light aircraft, such as a Cessna 150, take off at around 100 km/h (54 kn; 62 mph).

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