sector
In the schedule for an aircraft and its crew, the period starting with preparation of the plane before loading at one airport and ending with deplaning at the next.
sector: one takeoff-to-landing cycle in an airline schedule
A sector is a single flight leg from one airport to another, measured as the operational unit that determines crew duty times, aircraft maintenance checks, and revenue accounting. It begins the moment maintenance or a flight crew starts pre-flight preparation at the origin airport and ends when all passengers have deplaned at the destination. For a crew member, one sector counts as one duty period; for an aircraft, it is one cycle against fatigue life and maintenance thresholds.
The sector is the fundamental scheduling atom in airline operations. A crew roster might show a pilot assigned to four sectors in a day: London to Paris, Paris to Amsterdam, Amsterdam to Brussels, Brussels back to London. Each sector is priced separately in a passenger fare, tracked separately in fuel burn and emissions reporting, and audited separately for crew rest compliance under aviation authority regulations. A narrow-body airliner on a European network might fly eight to ten sectors daily; a long-range wide-body might complete two or three.
Maintenance checks are keyed to sectors flown, not hours. An A320 might require a walk-around inspection every 400 sectors, or a line maintenance check every 50 sectors. This is why airlines care deeply about sector length: very short sectors (under one hour) are operationally costly because the ratio of ground time to flight time is poor, and repeated takeoffs and landings accumulate wear faster than cruise flight. Conversely, long sectors allow the aircraft to be productive per check cycle.
Sector length and aircraft utilization
A sector is measured in flight time, not distance. A 90-minute flight is a 90-minute sector regardless of whether it covers 400 or 800 kilometers. Airlines optimize fleet assignment by matching aircraft type to typical sector length: regional jets serve 1 to 3-hour sectors, narrow-bodies handle 2 to 6-hour sectors, and wide-bodies are reserved for 8-hour-plus sectors where their fuel efficiency per seat justifies their higher fixed costs.
The term comes from the idea of dividing a route network into pieces or segments. In older contexts, sector also referred to a geographic subdivision of airspace assigned to an air traffic controller, but in crew and maintenance scheduling, the flight-leg meaning is now standard. Confusion occasionally arises because 'leg' is also used synonymously; sector is more formal in European and Commonwealth airlines, while North American operators often prefer 'leg' or 'flight segment'.