How Flying Works
How Flight Routes Are Planned — and Why Crews Change Mid-Flight
Singapore Airlines’ nonstop flight between Singapore and New York, SQ23/SQ24, is the longest scheduled commercial route in the world. It covers roughly 9,500 miles in 18 to 19 hours, on a specially modified Airbus A350-900ULR. No two pilots fly the whole thing. Four do: two captains and two first officers, taking turns at the controls while the off-duty pair sleeps in a dedicated two-bed rest compartment. It shows two things most passengers never think about together. How a route gets built before a flight leaves, and why the people flying it aren’t necessarily the same two people all the way.
The route is built by a dispatcher, not the pilot
Before any flight leaves, an airline dispatcher builds the proposed route. Working from the airline’s operations centre, usually with several flights at a time, they use planning software that produces several possible paths and the total fuel burn for each. The dispatcher weighs forecast winds, airspace restrictions, aircraft performance and alternate airports, then picks and refines the best option. In US operations, both the dispatcher and the captain then personally review and sign the dispatch release before the flight may legally depart. That’s real shared legal responsibility for the route and the flight’s safety. It’s split between two people who never fly together: one in an office on the ground, one in the cockpit.
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Why flight paths curve on a flat map
The Earth is a ball, so the shortest path between two cities, the great circle (blue), looks curved when the globe is flattened into a map. The line that looks straight on the map (dashed) is actually longer: for JFK–HKG it’s 16,399 km against 12,970 km, 3,428 km of extra flying. That’s why flights from New York to Asia head north over the Arctic. Real routes also bend for winds and airspace. Distances calculated from airport coordinates.
The real numbers
SQ23/24 — Singapore to New York, by the numbers
18-19 hrs
Flight duration
The world's longest scheduled commercial route
4 pilots
Cockpit crew carried
2 captains, 2 first officers, taking turns at the controls
13
Cabin crew, including purser
With their own dedicated rest area
2 beds
Pilot rest compartment
A dedicated, separate area from the cabin crew's bunks
Why the crew has to change at all
Flight Time Limitation (FTL) rules exist to prevent fatigue. They cap how long a pilot can stay at the controls without a proper rest period: not a nap in the spare seat, but a real break in a dedicated rest area. Under those rules no two-pilot crew may fly an 18-19 hour sector alone, which is why Singapore Airlines carries two full cockpit crews. Partway through the flight, the resting pair takes over. A formal handover briefing covers fuel, weather and anything still open. Responsibility passes across, and the pair coming off duty goes to rest. It’s the same shift-change routine used anywhere duty limits matter, just at 35,000 feet over an ocean. Cabin crew follow a related but separate set of rest rules. That’s why the aircraft carries 13 flight attendants with their own rest area, rather than only enough people to cover the flight if nobody needed a break.
None of this is unique to one airline or one aircraft. The same logic sits behind every extra-pilot crew on every very long route; it’s just most visible on the longest one. The route is planned on the ground, hours ahead, by people who never board the aircraft. The people who do board it aren’t necessarily the same two who land it. Neither is a compromise. Both exist because they make a very long flight measurably safer than asking one crew to do it all.
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Cost index: how fast should the flight go?
A route has a speed as well as a path, and the speed is a money decision.
Flying faster burns more fuel. Flying slower costs money too: crews are paid by the hour, maintenance is planned in flight hours, and late passengers miss connections. Airlines boil that trade-off down to one number called the cost index, which the crew enters into the flight management computer.
The cost index works like an exchange rate between time and fuel. A value of 50 kg/min, for example, says one minute saved is worth 50 kg of fuel. A cost index of zero tells the computer to ignore time and use the least fuel possible. The maximum tells it to fly as fast as the aircraft allows, whatever the fuel cost.
From that one number, the computer works out climb speed, cruise speed and when to start descending. A low cost index usually means a slower cruise, a higher altitude and a later descent. If a flight is running late, the airline may ask the crew to raise it and make up time. That is a business choice, not a safety one.
Sources & Further Reading
Common Questions
Frequently Asked Questions
Does the pilot choose the route?
Not from scratch. A dispatcher in the airline’s operations centre, often handling several flights at once, builds the proposed route with planning software, weather data and airspace restrictions. In US operations, both the dispatcher and the captain must review and sign the plan before departure. That’s real shared legal responsibility, not a formality.
Why can't the same two pilots just fly an 18-hour flight and rest in turns in their seats?
Because duty-time rules don’t allow it. Flight Time Limitation rules cap how long a pilot can be at the controls without a proper rest period, defined as time off operating duties. That’s why ultra-long-haul flights carry extra pilots and real bunks, rather than relying on someone napping in the spare cockpit seat.
How does a mid-flight pilot swap work?
One qualified pair of pilots hands control to another qualified pair already on board, using the same handover routine as any shift change. They brief the current situation, fuel, weather and anything still open before formally handing over. The outgoing pair then goes to the dedicated rest compartment for their scheduled break.
Do cabin crew have the same rest requirements as pilots?
A related but separate set of rules, set by each country’s regulator. That’s why Singapore Airlines’ 18-19 hour Singapore–New York flight carries 13 flight attendants with their own rest area, not just the four pilots.
Last reviewed: October 2026. Facts that change, such as fleets, airspace and airline ownership, are re-checked on a schedule. Spotted an error? Email contact@skyplus.news and we’ll fix it. See how we check facts.