Understanding Airplane Mode and Cell Signals

Airplane mode is named after the plane, but the federal ban on

phones in flight was written to protect the ground.

So what can your phone do to the ground?

Up there, too many towers can hear it.

Imagine you're flying home for Thanksgiving out of Chicago O'Hare.

You forgot airplane mode. As you climb, your phone hunts for

signal. On the ground, your phone talks to one nearby tower.

Each tower covers a patch called a cell.

That's why it's called a cellphone.

Channels are limited, so towers a few miles apart reuse the same

ones. That's called frequency reuse.

Down here, hills and buildings keep each phone local.

But here's where it gets clever. In the air, nothing blocks your

phone. It can reach towers across many towns at

once,

even towers reusing your channel for someone else's call.

So one phone in the sky can step on calls below.

That's why the FCC banned cellphones in flight in 1991.

It's still in force. So airplane mode mostly protects the

people down there. But there's another problem.

Is your phone harmless to the plane? Not quite.

A phone hunting for signal can send short bursts of radio.

Near the cockpit, pilots can hear them as a buzz in their

headsets.

It's minor, but during landing, pilots can't afford to miss a word,

so airplane mode cuts your cell radio.

But your iPhone keeps Bluetooth on, so your earbuds keep playing.

Wi-Fi can come back too, if the airline allows it.

So that little plane icon, it's mostly a favor to the towers

below.