It may be trodden on in flight (5)
I believe the answer is:
stair
'flight' is the definition.
(I've seen this before)
'it may be trodden on' is the wordplay.
I cannot quite see how this works, but
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is found within the answer.
The remaining letters 'sair' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'in' acts as a link.
Can you help me to learn more?
(Other definitions for stair that I've seen before include "section of flight" , "Set of steps" , "Flight unit" , "Indoor step" , "Component of flight" .)