Upbeat aircraftman in borders of Paraguay (5)
I believe the answer is:
perky
'upbeat' is the definition.
(I've seen this in another clue)
'aircraftman in borders of paraguay' is the wordplay.
'aircraftman' becomes 'erk' (I've seen this before).
'in' indicates putting letters inside.
'borders of' suggests removing the centre.
'paraguay' with its centre taken out is 'py'.
'erk' put inside 'py' is 'PERKY'.
(Other definitions for perky that I've seen before include "Lively, jolly" , "Cheerful, jaunty" , "Cheerful, lively" .)