Travel by air (3)
I believe the answer is:
fly
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">travel 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 fly that I've seen before include "SECOND PART OF 14" , "Glide" , "One invited into parlour" , "Insect; go quickly" , "Move through air" .)