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See also: the distinct shape of the flap and landing gear levers (which are often located next to each other).

https://aviation.stackexchange.com/questions/22680/why-is-th...

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... and yet on more than one occasion, pilots have taken off and prematurely retracted the flaps when they meant to retract the gear!

Humans fascinate me sometimes.

https://assets.publishing.service.gov.uk/media/578defbae5274...

https://assets.publishing.service.gov.uk/media/578def27ed915...

(Two separate incidents in the same year, on the same day, even)

EDIT: Updated links to point to incident reports

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