Ask Away: Any point to Aeroplane mode?

Is there any point to "flight mode"? Photo / Getty Images

I forgot to put my iPad on aeroplane mode during a recent flight. The battery did run down considerably during the flight, even though I did not use the plane's Wi-Fi. What's the worst that could have happened? - Anon

Although it's highly likely that a large number of phones are accidentally or intentionally left on in every flight and have been for a decade or so, I've consulted the internet and cellphones can and do interfere with planes.

When a phone is set near a speaker, it creates a "dit-dit-dit" tone that's pretty annoying. You've probably heard this interference yourself but perhaps not for a while. Aeroplane mode turns off the radios on your phone, preventing the issue.

Even modern phones will do this. When reception strength drops, the device will often try a GSM connection to see if they get a stronger signal.

"I've heard the "dit-dit-dit" interference from newer iPhones, it's not a "dumb phone" problem, said one pilot.

The "dit-dit-dit" sound is a problem when it is in pilots' headsets, interfering with their communication with Air Traffic Control.

It largely depends on where you're sitting as to how much trouble you can cause. "These days we only seem to hear the characteristic noise when the cellphone is transmitting while close to an active intercom line. For example, passenger in row 18 has an active cellphone while flight attendant at row 19 is talking on her intercom handset to the flight deck. It's not really interfering with radios as such, just being heard over an active analogue line amplifier," said another pilot on Reddit.

"I've been a pilot for 10 years and an air traffic controller for nine. I don't notice it as much flying but when I'm working, if another controller near the console has their phone we can tell. If they get a text you can often hear short bursts of static/buzzing through your headset. That being said, the phones in the breakroom don't do anything," another pilot added.

It's worth noting that these days many planes have a little cell tower aboard, just to keep any errant phones at low power levels.

American company AT&T has been known to send monstrous bills to people who leave their phone on during an international flight, by claiming that the tower connection represents roaming service. Another good reason to obey flight instructions.