Flight recorder (5,3)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">flight recorder</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for black box that I've seen before include "item revealing how Jumbo killed people?" , "Flight data recorder" , "Aircraft's flight recorder" , "Plane's flight recorder" , "Electronic device in aircraft recording flight information" .)