Why Don’t Airliners Take Off With Full Thrust?

Why Don't Airliners Take Off With Full Thrust?

An airliner’s departure, no matter where it is in the world, is usually an impressive show of noise and power. These characteristics are, of course, due to the forces used to lift the aircraft’s weight off the ground. Despite this, when it comes to thrust, an airliner can rarely use its maximum capability on takeoff. Why is this the case, though?

Pre-determined power

A determined decision based on several factors determines how much thrust an airliner uses to take off. This equation rarely results in a plane having to use all of its thrust capabilities to take off from a given runway.

Derated thrust occurs when an aircraft’s maximum capabilities are exceeded by a small amount of fuel. According to John Cox of USA Today,

“To reduce engine wear, most takeoffs use ‘derated’ thrust. Performance is measured for each takeoff, the required power setting is determined, and the thrust setting is made. This is known as a derated thrust takeoff because it is usually lower than the maximum available stage.

Why Don't Airliners Take Off With Full Thrust?

One of the most important benefits of using derated thrust is that it reduces engine wear. Photo: Vincenzo Pace | Simple Flying

For the sake of preserving the engine

The preservation of an aircraft’s engines, as Cox points out, is a vital factor in not departing at full speed. This has a positive effect on an airline’s bottom line. But, perhaps most significantly, it improves the plane’s safety. Cox goes on to say:

“Derates extend the life and efficiency of an engine. They reduce the risk of an engine failure while also lowering running costs. Derated or reduced-thrust takeoffs are used by all jets.”

The reduced probability of an engine failure reduces the likelihood of an accident involving the aircraft in question. Engine failures can be contained or uncontained. While several engine failures result in a successful emergency landing or aborted takeoff, reducing the risk of more serious accidents is still a worthwhile goal.

Why Don't Airliners Take Off With Full Thrust?

Engine wear and repair costs are reduced as thrust is reduced. Photo: Jake Hardiman | Simple Flying

Derated thrust leaves space to adjust

Pilots can, of course, change thrust levels during their takeoff roll if required. This is made possible by the use of derated thrust in the first place, as well as the length of runways in general. Cox mentions the following increases in thrust levels during takeoff:

“If the situation calls for it, you can always increase to maximum power when using this system during takeoff. Whether to use full thrust or derate is often decided by the captain.”

Overall, several interesting factors came together to lead to the decision to use derated thrust for the majority of departures. With more room to change and less engine wear as a result, it’s comforting, if unsurprising, to know that safety is a priority.

Did you know that when an aeroplane takes off, it seldom uses maximum thrust? Perhaps you’ve been aboard when the plane’s entire power supply has been used? In the comments, please share your thoughts and experiences.

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Cover Photo Credit: Vincenzo Pace | Simple Flying