What does F/O mean in Aircraft & Aviation?

First officer

In commercial aviation, the first officer is the second pilot of an aircraft. The first officer is second-in-command of the aircraft, to the captain who is the legal commander. In the event of incapacitation of the captain, the first officer will assume command of the aircraft. Control of the aircraft is normally shared equally between the first officer and the captain, with one pilot normally designated the "pilot flying" and the other the "pilot not flying", or "pilot monitoring", for each flight. 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. Many airlines promote by seniority only within their own company. As a consequence, an airline first officer may have more flight experience than a captain, by virtue of having experience from other airlines or the military. Traditionally, the first officer sits on the right-hand side of a fixed-wing aircraft and the left-hand side of a helicopter.

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