Airline covering up a beastly cry (3)
I believe the answer is:
baa
'beastly cry' is the definition.
(noise made by a sheep)
'airline covering up a' is the wordplay.
'airline' becomes 'BA' (British Airways).
'covering up' is an insertion indicator.
'ba' going around 'a' is 'BAA'.
(Other definitions for baa that I've seen before include "Sheep's cry" , "Sound of sheep" , "Sound of a lamb" , "Lamb's cry" , "Sheep's bleat" .)