The rules around smartphones on planes: What happens when you drop your phone into a plane seat?

You're strapped in on an aircraft taxiing to the runway and a fellow passenger just a couple of seats away is texting or scrolling through social media posts. The crew don't know – they're all buckled in as well. Does it matter? Happens all the time, possibly on most flights, but if you're worried, there is no definitive proof that any aircraft has fallen from the sky due to illicit smartphone usage. However that's no reason to break the rules.

Chances are we might have developed a close and meaningful relationship with our smartphones over the past two years, but the rule is that personal electronic devices (PEDs) capable of transmitting and receiving signals must be switched to flight mode on board an aircraft. Unless told otherwise by flight crew, PEDs may be used at all stages while on board an aircraft, the so-called gate-to-gate facility.

It wasn't always so. Until 2014, passengers were required to turn off all PEDs until advised, usually after the aircraft had climbed above 10,000 feet. Some grumbled, a few broke the rules. When he refused to stop gaming on his phone after his aircraft had been pushed back from the gate, Hollywood's Alec Baldwin was shunted back to the terminal and offloaded.

Late in 2013, based on a report by the PED Aviation Rulemaking Committee, the US Federal Aviation Administration (FAA) rewrote the rulebook for PEDs aboard US carriers. The committee found that if they were not receiving or transmitting via a cellular network, interference from PEDs was not a threat to the safety of commercial airliners. In response, the FAA decided that airlines could safely expand passengers' use of PEDs during all phases of flight.

The European Aviation Safety Agency quickly echoed the FAA ruling while in Australia, the Civil Aviation Safety Authority recommended that airlines use their own discretion regarding the use of PEDs infight, provided such use did not compromise air safety.

While the restriction on texting and phone calls caused some angst – and a few broke the rules - since the advent of inflight Wi-Fi, the heat has gone out of the argument. Provided you're using the aircraft's Wi-Fi system rather than a cellular connection, you can make calls using Viber or Skype, send WhatsApp messages and amaze your besties with Instagram posts of your aircraft's wing.

The battery problem

The other problem with smartphones on aircraft is the lithium-ion battery. In September 2016, passengers on an inbound Qantas flight from Los Angeles to Melbourne woke in the early morning to the smell of burning rubber. A business-class passenger had dropped a mobile phone into the innards of their seat. When the passenger moved the seat to try and retrieve it, the phone was crushed, rupturing the battery and generating enough heat to set the seat smouldering. Cabin crew reportedly raced through the plane with fire extinguishers and all ended well. Two years previously a similar incident happened aboard a Qantas flight from Sydney to Los Angeles, also in business class. In that case the phone caught fire, and again Qantas cabin crew saved the day.

The lithium-ion battery is between 2-10 times more energy dense than other battery technologies. That gives them more grunt in a small package, and more power to get you uphill on an e-bike, more shots on your digital camera, more life on your laptop and much longer time on your smartphone. However they have flammable electrolytes and if they're inadequately insulated or if the separators between the anode and cathode are too thin, it's a fire hazard. That's why lithium-ion batteries must be carried as hand luggage on flights, not checked in the hold. Also why many airlines won't carry lithium-ion batteries on cargo flights. A flaming phone in the cabin can be extinguished, that same phone on fire in the cargo hold is a death sentence. Even the powerful lithium-ion batteries Boeing developed for its 787s have had problems. In 2013 the U.S. Federal Aviation Administration grounded the entire 787 fleet of US-based carriers for six months after fires broke out on ANA and JAL 787s, caused by lithium-ion batteries.