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How a Plane Knows Where It Is

2 min read

The short answer

An airliner knows where it is using several separate systems at once — satellites, built-in motion sensors and radio beacons on the ground. The plane's computers constantly compare them, and air traffic control watches every flight too. If one source has a problem, the others carry on.

Never Just One Way

A plane in cloud or at night can't see where it's going. So it uses several independent ways to know its position — and never depends on any single one.

1. Satellites

Like the map on your phone, airliners use satellite navigation, often called GPS. It's very accurate and is used on most flights.

2. Motion Sensors That Need Nothing From Outside

Every airliner also has an inertial reference system. It uses extremely precise sensors to measure every tiny movement and turn the plane makes. From that, it works out where the plane is.

The clever part: it needs no signal from outside at all. It can't be blocked or interfered with. It's like knowing exactly where you are in a dark room because you counted every step.

3. Radio Beacons on the Ground

Across the world, ground stations send out radio signals. The plane's receivers use them to measure direction and distance. Close to airports, special radio beams guide the plane right down to the runway. Read landing in fog.

The Computers Cross-Check

The plane's flight computers blend all these sources together. If one disagrees with the others, the pilots are alerted, and the computer simply leans on the sources that agree.

Someone Is Watching From the Ground

Air traffic control sees each flight on its screens and talks to the pilots throughout. That's another check, completely separate from the plane. Read how air traffic control works.

The Takeaway

A plane is never lost. It has several ways of knowing exactly where it is, computers checking them against each other, and people on the ground watching too.

Sources

Keep reading

GPS Jamming in the News: Why Planes Still Know Where They Are

What GPS jamming is, why it's been in the news, and why planes keep navigating safely using their other systems.

How Air Traffic Control Works

How air traffic controllers keep thousands of planes a safe distance apart every day — with backups on board too.

Backup Systems: A Spare for Everything That Matters

How planes are designed so that no single fault can put a flight at risk — with backups for every important system.

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