In aviation, the flight length is defined as the distance of a flight. Commercial flights are often categorized into long-, medium- or short-haul by commercial airlines based on flight length, although there is no international standard definition and many airlines use air time or geographic boundaries instead. Route category lengths tend to define short-haul routes as being shorter than 600–800 nmi (1,100–1,500 km), long-haul as being longer than 2,200–2,600 nmi (4,100–4,800 km), and medium-haul as being in-between.
While they are capable of flying further, long-haul widebodies are often used on shorter trips: 40% of A350 routes are shorter than 2,000 nmi (2,300 mi; 3,700 km), 50% of A380 flights fall within 2,000–4,000 nmi (2,300–4,600 mi; 3,700–7,400 km), 70% of 777-200ER routes are shorter than 4,000 nmi (4,600 mi; 7,400 km), 80% of 787-9s routes are shorter than 5,000 nmi (5,800 mi; 9,300 km), 70% of 777-200LRs flights are shorter than 6,000 nmi (6,900 mi; 11,000 km) and 777-300ERs flights are evenly distributed across its range.
From 11 October 2018, the longest commercial flight is the Singapore Airlines Flight SQ 21/22 between Singapore Changi and New York/Newark, covering 15,344 km (9,534 mi; 8,285 nmi) with an Airbus A350-900ULR in nearly 19 hours, with 161 seats: 67 Business and 94 Premium Economy.
The absolute distance between two points is the great-circle distance, which is always the shortest geographical route. In the example (right), the aircraft travelling westward from North America to Japan is following a great-circle route extending northward towards the Arctic region. The apparent curve of the route is a result of distortion when plotted onto a conventional map projection and makes the route appear to be longer than it really is. Stretching a string between North America and Japan on a globe will demonstrate why this really is the shortest route despite appearances.
The actual flight length is the length of the track flown across the ground in practice, which is usually longer than the ideal great-circle and is influenced by a number of factors such as the need to avoid bad weather, wind direction and speed, fuel economy, navigational restrictions and other requirements. In the example, easterly flights from Japan to North America are shown taking a longer, more southerly, route than the shorter great-circle; this is to take advantage of the favourable jet stream, a fast, high-altitude tail-wind, that assists the aircraft along its ground track saving more time and fuel than the geographically shortest route.
Air time is the elapsed time that the aircraft is airborne, regardless of what time-zone the flight began and ended in.
Schedule time is the difference between the scheduled local time at the origin and the scheduled local time at the destination and usually differs from the actual time in the air as it is affected by the local time zones. Local clock time flying westward, or "chasing the sun", is slowed, while local clock time flying eastbound is sped up. However, flights over the International Date Line located at approximately 180o E in the Pacific will subtract 24 hours from the schedule time going eastwards and add 24 hours going westwards. For example, the eastward flight shown in the example from Japan to North America will have a scheduled time of arrival earlier than the departure time, while from North America to Japan the flight will take a whole day longer by local time; the actual flying time in both cases being the same or similar.