Reportedly, fuel needed for one taking flight across seas (6)
I believe the answer is:
petrel
'for one taking flight across seas' is the definition.
(type of bird)
'reportedly fuel' is the wordplay.
'reportedly' shows a homophone (sound like).
'fuel' becomes 'petrol' (petrol is a kind of fuel).
'petrol' sounds like 'PETREL'.
'needed' is the link.
(Other definitions for petrel that I've seen before include "Mother Carey's chicken" , "18's [BIRD]" , "Seabird sounds like fuel" , "Bird of storms at sea" , "Seabird (that may be stormy)" .)