Study of flight (11)
I believe the answer is:
aeronautics
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">study of flight</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 aeronautics that I've seen before include "The study of flight" , "Science of flight" , "Science of flying" .)