Then why do airlines still require phones to be switched off or put on airplane mode?
According to Mr Daniel, switching the mobile phone off or putting it on airplane mode reduces the high-intensity radiated field, especially during the critical phases of take-off and landing that require aircraft instrument sensitivity.
“The more passengers that turn off and reduce that HIRF effect, the better is for the aircraft avionics.”
But there is a bigger reason for telling passengers to turn off their phones – to make them pay attention to the flight crew and not be distracted during the safety briefing, he said.
What is the difference between using a phone during take-off and landing as opposed to cruising?
A mobile phone not switched off or set to airplane mode would actively send beacon signals, searching for a base station or cell tower in an attempt to connect to a cellular network.
At high altitudes, where a phone is unable to connect, the only consequence is that this would drain its battery faster, said Dr Venkatarayalu.
But during take-off and landing, the phone will likely connect to a cell tower.
Take-offs and landings are the most eventful and critical phases of the flight, when pilots rely heavily on navigational and communication equipment, said Mr Daniel.
The chances of an adverse event happening at altitude are much lower, he added.
Should you switch off your phone instead of leaving it on airplane mode?
“The deal about the airplane mode is it doesn’t necessarily turn off the Bluetooth or Wi-Fi, it just reduces the amount of signalling on the device,” said Mr Daniel. Turning off the phone would completely block the signals.
Dr Venkatarayalu explained that the emissions from a mobile phone are different in different modes.
In airplane mode with Wi-Fi turned off, functions that cause “intentional emissions” are shut down, he said.
“The leftover unintentional emissions during other usages such as, say, playing games, are so weak in strength that any other airplane equipment in the vicinity will have sufficient immunity, both by design and by requirement.”
Even when using a phone with the Wi-Fi on, the signals emitted are still too weak to cause major impact to the functionality and operations of airplane equipment, added the associate professor.
“While it may not be necessary to turn off entirely, it is certainly a good practice to follow all the in-flight announcements and instructions provided by the airline,” said Dr Venkatarayalu.