Travel Question: How safe is it to use a mobile phone on a flight?

Q My 20-year-old daughter is a very nervous flyer. She recently bit the bullet and flew on her own from Bristol to Dublin. She was horrified that a fellow passenger was using his smartphone to access the internet during the flight. Is this safe? A search suggests conflicting rules on different airlines and jurisdictions.

Name withheld

A Most airlines demand that phones are switched off, or to “flight safe” mode, from the moment the doors are closed on departure to the time the plane turns off the runway on arrival.

The idea is to prevent these portable electronic devices (PEDs in aviation shorthand) transmitting signals. There have been fears that electromagnetic emissions could interfere with the electronic systems on board planes.

Many passengers ignore the rules, and I am not aware of any incidents in which using a mobile phone has endangered an aircraft in flight. Some reports of a crash of a Swiss commuter aircraft in 2000 implicated mobile phone use, but tests found no evidence that aircraft systems were harmed by electromagnetic interference.

One time when mobile phone use can present a danger is during low-visibility landings. If an auto-land facility, which depend on an accurate exchange of signals, is used, there is a possibility that a strong electromatic emission from a phone could interfere.

In such cases cabin crew should make a special announcement and make every effort to ensure passengers are cooperating. But otherwise my research suggests that there is no risk from using a phone or data in flight.

Having said that, I advocate at all time obeying the instructions of cabin crew, and it is concerning that the passenger does not appear to have done so.

Phones present a more significant danger to aviation when their batteries overheat. I suggest that they are carried into the cabin, not placed in hold baggage, so that any “thermal runaway” can be dealt with before it becomes a threat.

Every day our travel correspondent Simon Calder tackles a reader’s question. Just email yours to s@hols.tv or tweet @simoncalder