Aircraft reportedly doing something impossible? It's straightforward! (5,7)
I believe the answer is:
plain sailing
'it's straightforward' is the definition.
(if something is plain sailing it's straightforward)
'aircraft reportedly doing something' is the wordplay.
'aircraft' becomes 'plane' (plane is a kind of aircraft).
'reportedly' indicates a 'sounds like' (homophone) clue.
'doing something' becomes 'sailing' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'plane' sounds like 'plain'.
'plain'+'sailing'='PLAIN-SAILING'
'impossible?' acts as a link.
This may not be right. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for plain sailing that I've seen before include "Trouble-free progress" , "effortless progress" , "Smooth easy progress" , "Simple" , "Easy and unobstructed progress" .)