I have a guilty secret to confess. My plane was preparing for take-off from London’s Heathrow Airport in March when a flight attendant made the usual request for passengers to turn their electronic devices off. Far from complying, I pushed my smartphone deeper into my pocket. I had important work messages to check, and surely my little handset wasn’t going to cause the plane to plummet from the sky, was it?
It seems I'm not alone. A recent survey found around four out of 10 US air passengers admitted they don’t always turn their gadgets off on flights. One notable occasion saw the actor Alec Baldwin reacting furiously on Twitter after being kicked off a Los Angeles-to-New York flight before take off for refusing to stop playing the online game Words With Friends on his phone.
According to regulations, which are pretty uniform around the world, the use of portable electronic devices is not allowed below around 3,000m (10,000ft), even in "flight mode” which stops the transmission of signals. Above this height devices like laptops and music players can be used, but phones must remain off. These rules are important, we are told, to avoid potentially dangerous interference between signals from these devices and sensitive onboard electronic systems. But do these fears have any scientific basis, or is it time to relax the rules?
The fear of interference comes from the fact that gadgets connect to the internet or to mobile phone networks using radio waves. To explain the theoretical dangers, Peter Ladkin, Professor of Computer Networks and Distributed Systems at Bielefeld University, Germany, uses the analogy of holding a blowtorch to your household heating pipes. The central heating system in your house makes changes based on the readings of thermometers within those pipes, so the blowtorch will heat the water, change the temperature readings and trigger the system to make adjustments.
Personal mobile devices could act in a similar way on aeroplanes, on which hundreds of electronics-based systems, known as avionics, are used for navigation, to communicate with the ground and to keep track of the components that keep them in the air. Some involve sensors that communicate information to cockpit instruments. It's not just an issue with mobile phones. Kindles, iPods, laptops, handheld gaming consoles – they all emit radio waves. If these are at frequencies close to those of the avionics, signals and readings could be corrupted. This could affect systems such as radar, communications and collision avoidance technology, and the problem is potentially magnified if gadgets are damaged and start emitting stronger radio waves than they should, or if signals from multiple devices combine.
So much for the theory, but is there any proof that this is a problem? There are no known recorded incidents of crashes having been definitely caused by such interference, but that said the causes of accidents can sometimes remain unknown. A flight recorder may not identify that a critical system has failed because of electromagnetic interference from passengers’ devices.
But while definite proof may be lacking, there is plenty of anecdotal evidence that the risks should be taken seriously. A report summarising 50 cases of safety issues thought to have been caused by personal electronic devices, was published in January this year. These were compiled from the US Aviation Safety Reporting System, a database maintained by Nasa, to which crew members can anonymously submit reports of safety problems. One such case was summarised as follows: "First Officer reports compass system malfunctions during initial climb. When passengers are asked to verify that all electronic devices are turned off the compass system returns to normal.”