Here's Why You Have to Switch Your Phone to Airplane Mode On a Flight

There's hype around putting phones on airplane mode during a flight. But what's it all for?

There are a lot of rules on airplanes. Some are unspoken, personal, and up for interpretation (don't recline your seat while the person behind you is eating; don't go into the lavatories barefoot), while others are official policy, announced over the intercom before a flight's departure. And after we've been asked to buckle our seat belts, put our tray tables up, and move our seats forward, we hear it: the request to turn our electronic devices off completely, or put them on airplane mode. But given that we can use our mobile devices nearly anywhere these days—and hey, that there's strong WiFi at 35,000 feet—what's this all about? If you do leave your phone on, how does it affect the plane?

For starters, it's mostly about safety. And while the U.S. ban was initially implemented in the 1990s over fears about mobile frequencies leading to a malfunction of the plane's electronic systems—or worse yet, a crash—there is no evidence that this has ever been the case. Still, pilots have noted that cell phones transmitting signals can cause audible interference on the aircraft’s radios, likening it to the sound of a CD skipping. This interference, in turn, could potentially block radio frequency for one or two seconds and lead to confusion between the pilots and air traffic control.

Whether a phone will cause such interruption depends on a variety of factors: if the device is sending or receiving a call at the edge of cell reception (typically between 5,000 and 10,000 feet), proximity of the phone to the cockpit, and the model of device. One pilot estimated hearing such blips on 2-3 percent of his flights, and with new planes, phones, and updated on-board technology, it is becoming even rarer. As for what happens to passengers who don't switch their phones to airplane mode? Short of a reprimand from a flight attendant, not much.