Friday, May 29, 2020

Why do you need to turn off all your electronic devices before an airplane takes off and lands?

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have a guilty secret to confess. My plane was preparing for take-off from London’s Heath row 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?

Person Holding Smartphone Riding Airplane

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.

People Walking Beside Baggage Hall and Arrivals Hall Signage

System malfunction

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.”

A 2006 analysis of the database identified 125 reports of interference from electronic gadgets, of which 77 were defined as "highly correlated". In one incident a 30-degree error in navigation equipment was immediately corrected when a passenger turned off a portable DVD player. This problem reoccurred when the device was switched back on. Fight crew have reported a number of similar cases in which they have watched readings on navigations systems change apparently in response to passengers being asked to turn specific devices on and off. In another report, the International Air Transport Association (IATA) identified 75 separate incidents of possible electronic interference that pilots believe were linked to mobile phones and other electronic devices between 2003 and 2009.

In the competitive world of aviation, some airlines such as Virgin Atlantic and Delta Airlines have started advertising the use of technologies that allow greater use of mobile devices on flights. In-flight mobile phone systems such as OnAir and AeroMobile use miniature on-board base stations called picocells which allow devices to transmit at lower power levels. Transmissions are processed, transmitted to a satellite and then on to the normal ground networks. This, says AeroMobile chief executive Kevin Rogers, enables the use of mobiles “as a roaming service just like when you go to a foreign country, except that in a foreign country you don’t need a satellite link.” Some airlines are now starting to fit AeroMobile equipment during production.

These systems allow you to use your phone while at cruise altitude, but not during take-off and landing. Rogers thinks that this might change one day, but at the moment it is still difficult to “prove categorically that there is indeed no interference – so airlines tend to err on the side of caution and be conservative.”

But as Rogers adds: “Many phones are always left on anyway. If there was a real risk of interference of a mobile phone or an iPad with the aircraft’s systems, people would not be allowed to take them on the aircraft at all.”

Some air authorities remain unconvinced, however. In-air mobile services cannot be used in US airspace, for example. The US Federal Aviation Administration has come under pressure to relax its rules and last year set up a group of experts to study the question. A decision is expected by the end of this year.

Richard Taylor, a spokesman of the UK’s Civil Aviation Authority, believes it is just a matter of time before we see more widespread use of mobile devices on aircraft, but that calls will remain banned during take-off or landing for the foreseeable future.

“When regulators like us are convinced that an aircraft can be used safely even with portable electronic devices being used in the cabin, that the signal being emitted from the cabin at any stage of the flight can be safely absorbed without affecting any of the aircraft systems, of course the rules will be relaxed,” he says. “But it’s up to the manufacturers, and of course to the airlines, to prove that they are operating the aircraft safely.”

Perhaps that day may come soon. However, having learnt how difficult it is to prove definitively that planes are safe from interference, I'll be making sure my phone is properly switched off in future. After all, when I'm en route to my holiday in the sun, I don't want my handset to be responsible for tricking the pilot into landing in some rainy old place. Or for something even worse.


“We don’t make you stow your laptop because we’re worried about electronic interference. It’s about having a projectile on your lap. I don’t know about you, but I don’t want to get hit in the head by a Mac Book going 200 miles per hour.” -Patrick Smith
“People don’t understand why they can’t use their cell phones. Well, what can happen is 12 people will decide to call someone just before landing, and I can get a false reading on my instruments saying that we are higher than we really are.”

“We’re not trying to ruin your fun by making you take off your headphones. We just want you to be able to hear us if there’s an emergency.

There has been a lot of debate about the effects of electronics on aircraft, but nobody has clearly shown any real risk from laptops, DVD players, etc. I see in one of the answers there appears to be a potential issue from poorly designed FM radios, but cannot comment on that. The FAA is primarily concerned about potential threats to the aircraft, and they seem to be heading towards allowing devices to be used during flight, which indicates they do not believe that interference with aircraft equipment is a problem.

That being said, the FAA still wants equipment off and stowed during pref light safety briefing and takeoff to cruising altitude. This is due to safety - a) so passengers pay attention to the safety briefing, and b) in case there is an accident and the need to evacuate the aircraft - have a bunch of laptops on and the like in the cabin will impede evacuation and may injure passengers in case of a rough landing (or crash).

The ban on using mobile phones comes from the FCC, a different government agency, and is not done out of safety concerns for the aircraft. Instead, the FCC is worried about the mobile network and cell towers. Cell phones will camp on to the strongest tower, then, if you are moving, occasionally switch the phone between towers as you move. On the ground, there will be one or two towers that are close, and a few more that you can connect to, but are weak signals. Moving on the ground, you will be handed off between towers only occasionally, even at freeway speeds. Note this happens regardless of whether you are on a call or not.

However, if you are in the air, the situation is entirely different. You will be above and equidistant from all the towers in the area (at least until you get high enough that you have no signal). Instead of occasional handoffs between towers, your phone will hand off continuously between all the towers, tying up bandwidth and processing time on all of them, greatly reducing the capacity of the network to handle calls.

Some airlines do support cell phones during their flights. This is done by having the equivalent of a cell phone tower in the plane. As that is the strongest signal the phone can see, all the phones in the plane camp on that “tower,” and do not attempt to connect to any other tower, so no hand-offs, and no network impact.

So, once in the plane, set your phone to aircraft mode. That causes it to stop connecting to the mobile network, and eliminates the hand-off problem. Don’t turn off aircraft mode until you are on the ground again.

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