What happens if you don’t turn on phone’s flight mode when flying: Planes will stay up, but communications could go down

There’s little chance that leaving a phone turned on could actually cause harm to anyone — but it could be a significant annoyance

Then Democratic presidential hopeful Barack Obama talks on his cell phone as he boards his campaign plane at Midway Airport en-route to Washington DC, May 7, 2008 (Mark Wilson/Getty Images)

Not turning a phone’s flight mode on when flying isn’t likely to bring a plane down — but could still cause huge problems for people flying in them.

While there’s little danger from leaving a phone’s connection online when flying, the signals can interfere with communications and cause annoying problems for pilots.

Those problems are something like the noise that can be heard when a phone rings near to a speaker: a slow, percussive thumping. But instead of coming out of a speaker it can be heard through the headsets that are worn by pilots.

Even that is fairly rare — of 50 flights, pilots might hear them once or twice. It isn’t clear whether the relatively small number of problems is a consequence of issues being rare or people mostly remembering to turn off their phones.

Sometimes larger communications problems come into play. At least one person has interrupted a radio call between their plane and traffic control, the Mail reported, potentially causing danger for those on board and in other planes.

But generally leaving flight mode on is likely to cause any big problems. Some airlines even let their passengers use a version of their phone networks — allowing people to connect to special carriers while in the air that then allow them to text and call for extra charges.