Where an airplane might disappoint the pilot? (3-4)

I believe the answer is:

let-down

I'm a little stuck... Click here to teach me more about this clue!

'disappoint the pilot?' is the definition.
'let down' can be an answer for 'disappoint' (synonyms). I am unsure of the 'the pilot?' bit.

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for let-down that I've seen before include "Anticlimax" , "Disappointment" , "It's disappointing" .)

I've seen this clue in the Evening Standard.

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