I am sure you have heard or seen the warning sign to turn of your mobile devices when you’re about to take off in an aeroplane.
But what if you didn’t switch off your mobile? Will you cause an accident?
Flying would be very scary if anyone one of us did not switch off our phone during a flight. If that was really the case, then airplanes would have those devices seen in movies where mobile signals are blocked within a certain radius.
But if mobile phones are harmless, then why do they ask us to switch off or put our phones on Airplane Mode during each flight.
The problem lies with your mobile phone trying to make contact with the nearest ground tower. According to Wikipedia, “In the United States, the Federal Communications Commission (FCC) restricts cell phone usage on aircraft in order to prevent disruption to cellular towers on the ground.”
The premise given is that most mobile phone towers were not designed to keep track of mobile phones whizzing around them at around 400 km/h. Most mobile phone towers have a donut shaped range – any handphone in this range gets captured by the mobile tower.
Source of pictures: Datasync
The vertical range is about 8000 feet or 2400 meters.
A plane traveling at an altitude of 1000 feet or 300 meters at 500 knots will have a window of opportunity to get a signal in the white region shown below. The grey region is the region with no signal due to the Doppler Blocking effect.
At a slower speed, the window of opportunity widens.
In other words, during take off and landing is your best chance to make calls as the window of opportunity to get a decent cell phone signal drops of as the plane speeds up. Even then, at 500 knots and a 5-second gap, several hundred mobile phones trying to make contact with a mobile phone tower is a pretty traumatic event for the mobile tower.
Another amazing fact is that phone signals can only escape from an aeroplane via its windows. The aeroplane is encapsulated via a law attributed to Michael Faraday known as Faraday’s Cage:
A Faraday cage or Faraday shield is an enclosure formed by conductive material or by a mesh of such material. Such an enclosure blocks external static and non-static electric fields by channeling electricity along and around, but not through, the mesh, providing constant voltage on all sides of the enclosure. Since the difference in voltage is the measure of electrical potential, no current flows through the space. Faraday cages are named after the English scientist Michael Faraday, who invented them in 1836.
Scientific reasons are not the only explanation why mobile phones are not allowed on planes. A social explanation is that passengers expect quietness on the plane. Just imagine if everyone was allowed to use their mobile phones in a confined aeroplane. It would be a disaster.
Furthermore, an economic reason is that aeroplanes have always provided telephone services at a cost. Why lose this stream of revenue?
So, the moral of the story is that your mobile phone, if it ever rings on the plane, will not bring the plane down. But having the mobile phone off during flights gives passengers a peace of mind during their “confinement” in the plane.
And that is priceless!