In commercial aviation, the aircrew are called flight crew. Some flight crew position names are derived from nautical terms and indicate a rank or command structure similar to that on ocean-going vessels, allowing for quick executive decision making during normal operations or emergency situations. Historical flightdeck positions include:
Captain, the pilot designated as the Pilot-In-Command (PIC), and the highest-ranking member or members of a flight crew.
First Officer (FO, also called a co-pilot), another pilot who is not the pilot-in-command, and is normally seated to the right of the captain. (On helicopters, an FO is normally seated to the left of the captain, who occupies the right hand seat).
Second Officer (SO), a person lower in rank to the First Officer, and who typically performs selected duties and also acts as a relief pilot. The rank of Second Officer was traditionally a Flight Engineer, who was often the person who handled the engine controls. In the 21st century second officers on some airlines are pilots who act as "cruise relief" on long haul flights.
Third Officer (TO), a person lower in rank to a Second Officer, and who typically performs selected duties and can also act as a relief pilot. Largely redundant in the present day.
'Relief Crew' members in the present day are fully licensed and trained Captains and First Officers who accompany long-haul airline flights, and who relieve the primary pilots during designated portions of the flight to provide them with rest or sleep breaks (some large wide-body airliners are equipped with special pilot sleeper berths, but more typically reserved seats in the section closest to the flight deck, or cockpit, are used for the relief crew). The number of relief crew members assigned to a flight depends in part on the length of the flight and the official air regulations the airline operates under.
Flight Engineer (FE), a position originally called an 'Air Mechanic'. On older aircraft, typically between the late-1920s and the 1970s, the Flight Engineer was the crew member responsible for engines, systems and fuel management. As aircraft became increasingly sophisticated and automated, this function has been mostly assumed by the primary pilots (Captain and FO), resulting in a continued downsizing in the number of aircrew positions on commercial flights. The Flight Engineer's position is commonly staffed as a Second Officer. Flight engineers can still be found in the present day (in greatly diminished numbers), used on airline or air freight operations still flying such older aircraft. The position is typically crewed by a dual-licensed Pilot-Flight Engineer in the present day.
Airborne Sensor Operator, An airborne sensor operator (aerial sensor operator, ASO, Aerial Remote Sensing Data Acquisition Specialist, Aerial Payload Operator, Police Tactical Flight Officer, Tactical Coordinator etc.) is the functional profession of gathering information from an airborne platform (Manned or Unmanned) and/or oversee mission management systems for academic, commercial, public safety or military remote sensing purposes. The airborne sensor operator is considered a principal flight crew or aircrew member.
Navigator (archaic), also called 'Air Navigators' or 'Flight Navigators'. A position on older aircraft, typically between the late-1910s and the 1970s, where separate crew members (sometimes two navigation crew members) were often responsible for the flight navigation, including its dead reckoning and celestial navigation, especially when flown over oceans or other featureless areas where radio navigation aids were not originally available. As sophisticated electronic air navigation aids and universal space-based GPS navigation systems came online, the dedicated Navigator's position was discontinued and its function was assumed by dual-licensed Pilot-Navigators, and still later by the aircraft's primary pilots (Captain and FO), resulting in a continued downsizing in the number of aircrew positions on commercial flights. Modern electronic navigation systems made the navigator redundant by the early 1980s.
Radio Operator (archaic). A position on much older aircraft, typically between the mid-1910s and the 1940s, where a separate crew member was often responsible for handling telegraphic and voice radio communications between the aircraft and ground stations. As radio sets became increasingly sophisticated and easier to operate, the function was taken over directly by a FO or SO, and still later by the pilot-in-command and co-pilot, making the radio operator's position redundant.