To which the flight engineer holds the key? (7)
I believe the answer is:
airlock
'key?' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe they are linked in a way I don't understand?
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for airlock that I've seen before include "obstruction" , "plumbing problem" , "Bubble obstructing flow" , "chamber?" .)