A pair on part of airfield (5)
I believe the answer is:
apron
'part of airfield' is the definition.
('apron' is part of 'airfield')
'a pair on' is the wordplay.
'pair' becomes 'pr'.
'a'+'pr'+'on'='APRON'
(Other definitions for apron that I've seen before include "Protective garment - type of stage" , "skirt" , "Pinny -part of the fairway leading onto the green" , "stage perhaps" , "Paved area where aircraft are parked" .)