First officer (aviation)

In aviation, the first officer (FO), also called co-pilot, is a pilot in addition to the captain, who is the legal commander.

Even when the first officer is the flying pilot, however, the captain remains ultimately responsible for the aircraft, its passengers, and the crew.

In typical day-to-day operations, the essential job tasks remain fairly equal.

[3] On a long haul flight, there may be multiple captains and first officers on board, to act as relief crew.

While the captain rests, the senior of first officers sits in the left-hand seat, as for example on Air France Flight 447.