eli5: Why do planes need to dump fuel before landing?

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I have just seen that a BA flight from London to Miami took a 2 hour detour to use up fuel before heading to its destination. It is not the first time I have heard of this.

Why do planes need to use up/dump the fuel before landing? Surely it’s better to be safe and have more than enough fuel for the entire journey therefore not use up a full tank just before landing?

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7 Answers

Anonymous 0 Comments

A little bit of further detail to expand on the answers that are already here… The plane’s computer keeps track of how much weight there is on board, including the plane body itself, passengers, luggage/cargo, and fuel. It uses that weight and the length of the runway it will be landing on (plus some other factors) to determine if it will have enough of a margin of error to safely stop the plane without going off the end of the runway or setting the brakes on fire, this is called the Maximum Landing Weight (MLW).

The plane must be under this weight when landing, otherwise it is considered an overweight landing which comes with a hefty dose of bureaucracy, required inspection, etc etc. Pilots don’t want to do that.

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