Metal flying machine loses height (6)
I believe the answer is:
copper
'metal' is the definition.
(copper is a kind of metal)
'flying machine loses height' is the wordplay.
'flying machine' becomes 'chopper' (term for a helicopter).
'loses' suggests deleting specific letters.
'height' becomes 'h'.
'chopper' with 'h' taken out is 'COPPER'.
(Other definitions for copper that I've seen before include "Metal, Cu" , "PC" , "An element; small coin" , "Metal - wash basin" , "Chemical element, symbol Cu" .)