What happens if you don't switch your phone to flight mode?

Have you ever wondered why cabin crew on commercial flights ask you to switch your phone to flight mode?

Some of us might feel it's unnecessary as it doesn't interfere with airplanes and is not a matter of life and death.

What if your cell phone signals cause interference and the crew misses a crucial radio call from air traffic control? So yes, it is important to swipe your phone to Airplane mode.

Many people wrongly believe that a phone's signal can interfere with a plane's electrical and telecommunication systems and cause a plane to crash.

It can cause occasional disturbance, but nothing really happens to the plane's mechanism.

Your phone will probably annoy a few pilots and air traffic controllers. But, most likely, not badly enough for them to take action against you, if that’s what you want to know.

You may have heard that unpleasant noise from an audio system that occasionally happens when a mobile phone is nearby. A phone's radio emissions can be very strong, up to 8W; they cause this noise due to parasitic demodulation.

It is not safety critical, but is annoying for sure.

Nowadays, the possibility of interference has largely been reduced by new technology, allowing some international airlines to permit in-flight calls.

These low-powered specially-designed systems, called picocells, don’t interfere with the flight crew's communications.

In a worst case scenario though, repeated interference from mobiles could cause the crew to miss a crucial radio call from air traffic control – so it’s best to stick to the rules.

In a blog for Airline Updates, a pilot said that transmitting mobiles can cause interference but it is rare.

He said: "You've probably heard this interference yourself when a phone is set near a speaker.

"It sounds like a 'dit-dit-dit-dit' tone and it's pretty annoying."

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