Factory to design aircraft's tail (5)
I believe the answer is:
plant
'factory' is the definition.
(a manufacturing plant)
'design aircraft's tail' is the wordplay.
'design' becomes 'plan' (synonyms).
'tail' says to take the final letters.
The last letter of 'aircraft' is 't'.
'plan'+'t'='PLANT'
'to' is the link.
(Other definitions for plant that I've seen before include "Shrub - factory" , "Member of vegetable kingdom" , "Factory; spy" , "Factory equipment" , "eg Flower" .)