Going by air (6)
I believe the answer is:
flying
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">going by air</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for flying that I've seen before include "Hasty" , "short" , "(Of flag) displayed on a flagpole" , "Travelling by plane" , "High speed steam engine (1923)" .)