Prepared to fly the sick in (7)
I believe the answer is:
willing
'prepared' is the definition.
(similar in meaning)
'fly the sick in' is the wordplay.
'fly' becomes 'wing' (synonyms).
'the sick' becomes 'ill' (I've seen this before).
'in' indicates putting letters inside.
'wing' placed around 'ill' is 'WILLING'.
'to' is the link.
(Other definitions for willing that I've seen before include "Ready and keen" , "game?" , "Amenable, consenting" , "Compliant" , "Ready and eager" .)