How Flying Works
Why 35,000 Feet? Altitude, Concorde, Fighter Jets and Jet Streams
The number on the seatback map, usually about 35,000 feet, looks random if you’ve never thought about it. It isn’t. It’s the answer to an engineering trade-off every commercial jet is built around. It also explains why Concorde, a modern fighter and a private Gulfstream all fly at different heights for three different reasons. None of them chose their altitude out of preference. All follow the same physics, using aircraft built to exploit different parts of it.
The physics behind the number
Two things happen as an aircraft climbs, and they pull opposite ways. The air gets thinner, which helps speed and fuel use: thinner air means less drag, so the engines work less hard at a given speed. But a jet engine also needs oxygen to burn fuel, and thinner air means less oxygen reaching the engine. Climb too high and the engines lose thrust faster than the drag falls, so the trade stops paying. For a typical airliner at a typical weight, the two effects roughly balance at about 35,000–38,000 feet. Drag has fallen a lot, but the engines are still breathing comfortably. The balance point varies from flight to flight, which is why real cruising heights range from about 30,000 to 42,000 feet, depending on the aircraft, how heavy it is and the winds at each level that day.
Try it
Climb the ladder: what changes with altitude
Airliners cruise in the shaded band, roughly 30,000–42,000 ft. Up there the air is thin, so there’s less drag, and it’s very cold, which helps jet engines work efficiently. At 37,000 ft the air is only 28% as dense as at sea level and about -56°C. Climb too high, though, and the wing struggles to make enough lift in the thin air. Values from the international standard atmosphere; real days vary.
Cold matters as much as thin air. At 35,000 feet the air averages about −54°C, and a jet engine works more efficiently in cold air: the colder the air coming in, the less work it takes to compress it before burning fuel. That’s also why a long-haul flight doesn’t level off once and stay there for eleven hours. As it burns fuel, the aircraft gets lighter, needs less lift, and can climb a little higher into thinner, more efficient air. This is called step climbing. A flight might leave at FL340 (34,000 feet) and be at FL380 or FL400 before it starts descending, with several changes of height along the way.
Concorde: the same physics, solved for a completely different speed
Concorde cruised at about 50,000 to 60,000 feet, nearly twice as high as a normal airliner, and the reason comes back to drag. At Mach 2, air resistance is a far bigger problem than at Mach 0.85, so Concorde needed thin air much more than a subsonic jet does. Its delta wing and afterburning Rolls-Royce/Snecma Olympus 593 engines were built to work in that thin, cold, high air, not merely cope with it. In service from 1976 to 2003, that height and speed let Concorde cross from London to New York in under three hours at best, roughly a third of a normal flight time. It came at a price, though. Concorde’s sonic boom meant supersonic flight was banned over populated land in most countries. That’s a big part of why its scheduled routes were almost all across the Atlantic, where the boom hit nobody, rather than worldwide. No airliner since has matched that height and speed. A normal airliner’s wings, engines and pressurisation are designed for a slower regime, and flying it at Concorde’s height would mean solving Concorde’s drag problem all over again.
Fighter jets: altitude as a weapon, not a fuel-saver
A modern fighter like the Lockheed Martin F-22 Raptor has a service ceiling of around 50,000 feet, and unofficial figures suggest it can go higher for short periods. But a fighter isn’t up there to save fuel like an airliner. For a fighter, height is a resource: it can be traded for speed in a dive, which is why fighters value it so highly. Getting a fighter high, fast, usually means using an afterburner, which burns fuel far faster than any airliner at cruise. A fighter’s mission accepts that cost because the payoff is worth it. An airliner never makes that trade, because it gets nothing for it except a bigger fuel bill.
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Private jets: buying altitude to skip the traffic
The newest long-range business jets, like the Gulfstream G650, are certified to 51,000 feet and usually cruise at about 45,000 feet, comfortably above most airline traffic. That’s deliberate, and the economics are different from an airliner’s. A G650 carries a handful of passengers, not 300, so the extra fuel cost of climbing higher matters far less against what each trip is worth. In return, flying above most airline traffic and most weather buys a smoother, quieter ride, fewer height restrictions from air traffic control, and often a more direct route, because the jet isn’t competing for the same crowded levels. It’s the same thin-air, cold-air efficiency curve every jet rides. Private jet owners simply pay more of the fuel cost to climb higher for comfort and directness, while airline economics push the other way.
The real numbers
Cruising altitude, by aircraft type
~35,000ft
Typical commercial airliner
Real range roughly 30,000-42,000ft, changing over a flight via step climbs
~45,000ft
Typical private jet cruise
Gulfstream G650 — certified ceiling 51,000ft
~50,000ft
F-22 Raptor service ceiling
Altitude used tactically, not for fuel economy
50,000-60,000ft
Concorde cruise altitude
Purpose-built to cut drag at Mach 2
How a route actually gets decided
The shortest path between two points on a globe is a great circle route, not the straight line a flat map suggests. That’s why a New York–Tokyo flight path curves up towards the Arctic on a map instead of running straight across the Pacific. Planning software starts from that shortest path, then adjusts it for what matters on the day: forecast winds at cruising height, turbulence, restricted or closed airspace, and how far a twin-engine aircraft may fly from a diversion airport at any point, covered in this site’s ETOPS article. Over the North Atlantic, routes aren’t chosen flight by flight at all. Ocean control centres at Gander (Canada) and Shanwick (Ireland/UK) publish a fixed menu of parallel routes called the North Atlantic Tracks twice a day. Eastbound tracks come out around 1400 UTC for the overnight crossing, and westbound tracks around 2200 UTC for the next day. They’re built around where that day’s jet stream actually is, which has its own article: Jet Streams: The World’s Real Rivers of Wind. Airlines don’t plot their own Atlantic crossing; they choose from that menu.
Why the same flight is faster one way than the other
The main reason a return flight almost never takes the same time both ways is the jet stream. It’s a fast river of wind right at cruising height, flowing mostly west to east. An eastbound flight rides it as a tailwind, and the return leg fights the same wind head-on. Between New York and London, the difference between the two directions is often 30–90 minutes. With named jet streams all over the world, including an odd one that runs backwards, the topic gets its own full article rather than a paragraph here: Jet Streams: The World’s Real Rivers of Wind.
Animated
Why New York–London and London–New York fly different paths
The jet stream (the flowing band) is a river of fast wind high up, blowing west to east. Eastbound flights (green) are routed right into it for a free push and arrive early. Westbound flights (red) are routed away from it, often curving north towards Iceland and Greenland, where the headwind is weaker, even though the path looks longer. Air traffic control publishes a fresh set of these North Atlantic tracks twice a day, because the jet stream moves. Band and tracks are illustrative; map and airports are real.
Try it
Ride the jet stream: New York ⇄ London
The aircraft flies through the air at the same speed both ways (about 490 knots here). What changes is the air itself moving: with a 80-knot jet stream behind it, the eastbound flight covers the ground at 570 knots, against it only 410. That’s why the same route can differ by over an hour each way, and how a British Airways 747 topped 800 mph over the ground in a storm-driven jet stream in February 2020. Assumes the average wind along the whole route; real winds vary.
Sources & Further Reading
Common Questions
Frequently Asked Questions
Is 35,000 feet a fixed rule?
No. It’s a sweet spot, not a rule. Airliners fly anywhere between roughly 30,000 and 42,000 feet depending on type, weight and winds. A long-haul flight often climbs in stages as it burns fuel and gets lighter, a technique called step climbing. Air traffic control assigns the actual altitude, and it can change several times on a long flight.
Why doesn't every plane just fly as high as possible?
Because thinner air cuts both ways. Less air means less drag, which helps. But a jet engine also needs oxygen to burn fuel, and above a certain height the air gets too thin for the engines to work efficiently, or eventually at all. Every aircraft has a ceiling where those two effects cross. Go higher and the savings from thinner air stop being worth what the engines lose.
Could a modern airliner fly as high as Concorde?
Not without a completely different design. Concorde didn’t fly that high for the view. It flew there to cut drag at Mach 2, which only a purpose-built supersonic airframe and engines could manage. A normal subsonic airliner’s wings, engines and pressurisation are all designed for a lower speed and height.
Do pilots choose the flight route themselves?
Pilots fly the route, but dispatchers and planning software build it hours before departure, and pilots review it and can ask for changes. Over the North Atlantic, ocean control centres publish a fixed menu of routes twice a day, built around that day’s jet stream. Airlines pick from that menu; they don’t invent their own crossing.
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.