flight engineer

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The crew member responsible for the mechanical performance of an aircraft in flight.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A member of the flight crew in aircraft who monitors and operates all aircraft systems.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the flight crewman responsible for mechanical operation while in flight