Moving rapidly (4)
(Other definitions for fast that I've seen before include "Secure; speedy" , "Go without food" , "Period without food" , "Rapid; abstain from food" , "Quick; firmly fixed" .)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">moving rapidly</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 "& 20 Maritime aircraft" , "Moving quickly" , "-- boat; -- buttress" , "''Those magnificent men in their ... machines'' (film theme song)" , "Travelling by plane" .)