How High and How Fast Do Planes Fly?

Up Where the Air Is Smooth

Most jets cruise at around 30,000 to 41,000 feet — roughly 9 to 12 kilometres up. That height is chosen for good reasons:

• Thinner air means less drag, so the plane uses much less fuel.
• Above most weather — most clouds and storms are lower down, so the ride is usually smoother.
• More time and more options — the higher a plane is, the more room the pilots have to handle anything unexpected.

Why Not Even Higher?

Higher still, the air becomes too thin. Wings need air to make lift, and engines need air to make power. Each plane has a best height, which depends on its weight and the day's winds. As it burns fuel and gets lighter, the pilots sometimes climb a little higher. These are called step climbs, and they're completely routine.

Every Plane Has a Height Limit

Planes don't just keep climbing. Several layers keep them well below their limit:

• An approved maximum height. Every airliner type has one, proven in testing. For the Boeing 737 MAX, it's 41,000 feet.
• A limit worked out for today. The flight computer calculates the highest sensible height for the plane's weight and the air temperature. It keeps a safety margin, so the plane can still turn and ride bumps comfortably. The pilots see this figure on their screens.
• The computer flags anything too high. If a cruising height above the day's limit is entered, the computer warns the pilots. On some planes, it won't accept it at all.
• Air traffic control assigns every height. Pilots must ask before climbing.
• The cabin is built for it. Cabin pressure is designed for the plane's maximum height. Read cabin pressure explained.

In practice, pilots treat the limit as a ceiling and cruise comfortably below it.

How Fast?

A Boeing 737 MAX cruises at about 79% of the speed of sound — roughly 840 km/h (520 mph) through the air. Most airliners cruise at somewhere around 800 to 900 km/h. A tailwind makes the speed over the ground faster, and a headwind makes it slower. That's why the same route can take longer in one direction.

Why It Feels So Slow

Up high, there's nothing nearby to judge your speed against. It's like watching a distant plane crawl across the sky, when it's really racing along. Your body also only feels changes in speed, not speed itself — so a steady cruise feels almost still.

Lower and Slower Before Landing

Planes start coming down long before they land, descending gradually over many miles. By the final approach they fly much lower and slower, with the flaps out so the wings can fly safely at low speed. Read about the landing sequence.

Short flights also cruise lower than long ones, and air traffic control sometimes keeps a plane at a lower height for a while. If your flight seems low or slow, it's almost certainly doing exactly what was planned.

Sources

• FAA, Reduced Vertical Separation Minimum (RVSM) — the airspace from 29,000 to 41,000 feet where airliners cruise: https://www.faa.gov/air_traffic/separation_standards/rvsm
• Military & Aerospace Electronics, Why commercial aircraft cruise around 35,000 feet — thinner air, less drag, above the weather: https://www.militaryaerospace.com/commercial-aerospace/news/55399427/why-commercial-aircraft-cruise-around-35000-feet
• SKYbrary, Boeing 737 MAX 8 — cruise speed Mach 0.79, ceiling 41,000 feet: https://skybrary.aero/aircraft/b38m
• EASA, CS-25 Large Aeroplanes, AMC 25.251(e) — maximum height set with a 0.3 g margin from buffet: https://www.easa.europa.eu/en/document-library/easy-access-rules/online-publications/easy-access-rules-large-aeroplanes-cs-25?page=12
• FlyByWire, A32NX MCDU PROG page — the recommended maximum height for today's weight and temperature, and the "CRZ ABOVE MAX FL" message: https://docs.flybywiresim.com/pilots-corner/a32nx/a32nx-briefing/mcdu/prog/
• eCFR, 14 CFR 25.1527 — Ambient air temperature and operating altitude (each plane's approved limits): https://www.ecfr.gov/current/title-14/section-25.1527