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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Anonymous 0 Comments

I find it a bit puzzling that such a long flight would have to ‘dump fuel’ (commercial airlines, to the best of my knowledge, do not have fuel-dump capabilities). The pilots would be well-aware of the fuel situation long before they start descent. Excessive fuel could be burned by making the descent and approach less effective, i.e. a “non-idle descent”. It is not hard for a big heavy plane to use huge amounts of fuel in a short time, even without altering the flight plan. Worst case, they’d ask to be put in a hold in the STAR near the destination airport at low altitude where the air is thicker, thus burning even more fuel to keep the speed.

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