The flight engineer is a flight-crew member, a position found on many older aircraft, who monitors and controls various aircraft systems but does not fly the aircraft.
A flight engineer (abbreviated FE) is a cockpit crew member whose job is dedicated to monitoring and operating various aircraft-systems; the flight engineer is not one of the pilots (although it is perfectly possible for a flight engineer to also be a certified pilot), but they are often no less essential to the safe operation of aircraft requiring them.
Flight engineers first became a thing on the large seaplane airliners of the 1930s (and very late 1920s), whose multiple finicky piston-engines and propellers came with far too many gauges and controls for the pilots to handle on their own without serious risk of missing or missetting something important. As land-based aircraft became ever larger and more complex, they, too, acquired the flight-engineer position, and said position acquired more and more things to monitor and adjust. Most of the large bomber aircraft of World War II and the postwar era, and all of the last generation of large postwar propliners, required flight engineers, as did first-generation jetliners (albeit with somewhat different duties from their propeller-powered partners).
Later on, however, as aircraft technologies became more advanced, the pilots, and, increasingly, the aircraft itself, were able to take on more of the tasks formerly requiring a flight engineer. This happened first on smaller, simpler aircraft (the first common airliners with two-person flightcrews were the dc-9-family and the boeing-737, both fairly small jetliners, which entered service in 1965 and 1967, respectively), but, by the early 1980s, even large widebody (twin-aisle) jets were doing away with the flight-engineer position - many to most of the tasks formerly performed by a flight engineer could now be done automatically by the aircraft itself, and the introduction of the workload-reducing glass-cockpit allowed the remainder to be assumed by the pilots. Very few of the Western airliners still in service today require a flight engineer (although they can still easily be found with cargo airlines, which tend to gravitate towards older, cheaper, secondhand aircraft); they hung on longer in the former Eastern Bloc, and most large military aircraft still use a flight engineer (although this may be starting to change in the not-too-distant future).
Some tasks commonly formerly performed by flight engineers:
- Starting up and shutting down the engines and monitoring their gauges (plus, for piston-engined aircraft, such things as mixture ratio and propeller pitch);
- Monitoring the hydraulic-systems of large aircraft;
- Controlling cabin-pressure and air-conditioning;
- Ensuring the proper operation of the aircraft's electrical-system;
- Transferring fuel between tanks on long flights to help maintain proper weight-and-balance;
- Operating the aircraft's weather-protection systems (windscreen wipers, anti-ice, etc.);
- Et cetera.