Science Questions

Why do some airlines permit the use of mobile phones?

Sat, 11th Aug 2012

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Rebone Sesoko asked:

Dear Chris,


Fact of fiction: do cell phones affect the operations of aeroplanes and why is it that some airlines allow the use of cell phones while airborne?


Kind regards,




Dominic -   There are essentially three reasons which are cited for why people havenít been allowed to use phones on aircrafts up until now.  The first one is that there have been suggestions that the radio waves from the mobile phones can interfere with the operation of the aircraft.  Secondly, it actually causes problems for the cell phone networks because phones work by finding out which transmitter mast is closest to the phone and then linking to that mast.  Now if you're up in the air, you can see an awful lot of masts and the network can't actually decide which mast to attach to.  And the third problem is the social aspect of it being rather anti-social to be shouting into your phone when you're in the air, on an aeroplane.

Chris -   People do that in my train all the time, It doesnít seem to bother them!

Dominic -   Yes, but of course, with the noise of the engines, you going to have to shout quite loud to speak to somebody in an aeroplane.  Now in fact, the evidence that phones interfere with aircrafts is very weak.  There have been studies done, certainly by Boeing, to look at flying aircrafts with and without phones on-board and there was some very weak evidence that the planes with phones on-board may have had slightly more incidents, but it was so weak, it was probably just down to chance.  So I think most airlines now donít believe that phones do interfere with aircrafts and you can get around the problem of having to decide which mast to attach to by having a transmitter on-board the aeroplane which uses the aeroplaneís own communication systems to route your call to whatever network you're using.

Chris -   Brilliant!  Thank you, Dominic.  I shall use my phone with impunity on the aeroplane and refer them to you if they tell me off. 


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There are numerous systems on an aeroplane that can be affected by electromagnetic radiation. Mobile phones emit very high levels in specific frequency bands and these certainly could affect some of these systems. Basically it is a cautious response to maintain safety. It takes a lot of effort to thoroughly rule out any possible problems from multiple use of mobile phones being operated on a plane. The aircraft's equipment is probably designed with a certain amount of shielding and will have some specification regarding interference levels. This may well be being exceeded in some cases but is also necessarily cautious in specification. It is up to individual airlines whether they choose to perform practical tests to satisfy themselves that the radiation from mobiles is safe but the consequence of being wrong may be very high.

In practice there is probably more than enough margin built in to the equipment design but it would be unwise to assume that because mobile phone's are ubiquitous they are competely benign regarding there ability to seriously interfere with electronic equipment. I certainly do not, as many seem to do, disregard the airline's instructions regarding mobile phone usage. graham.d, Mon, 23rd Jul 2012

At cruising altitude, there is time to recover in the unlikely event of interference; on takeoff and landing, there is no time to react. Another reason for turning off electronic devices during takeoff and landing (even non-transmitting ones) is so that people will hear safety announcements.

Normally, a mobile phone is used within 1km of a base station. In an aeroplane at cruising altitude, you are at least 10km from a base station, so the phone needs transmit at higher power, increasing the chance of interference to aeroplane systems.

Using mobile phones in an aeroplane is not very desirable from the viewpoint of the mobile network operator, as the plane is in line-of-sight of multiple base stations on the ground, and will cause widespread interference to the ground network. It will require rapid handovers between the nearest base station on the ground as the plane moves across the sky.

If an aeroplane had an onboard base station, the phones could transmit at very low power, since the base station is only meters away. The plane would need to provide a satellite connection back to the terrestrial network, which is another layer of complexity - some airlines avoid this complexity by having a phone handset in every seat which can call other seats in the plane, or make calls via satellite.

evan_au, Fri, 27th Jul 2012

It would seem like the hardware to wire up an airplane with a cell phone repeater would be relatively inexpensive.
Yet, the seat back phones are something like $10 a minute. 

Even with the seat back phones....  if they set the price to, say $0.50 a minute, the usage would be much higher, and I wouldn't be surprised if the revenue generated would actually exceed the current $10/min system.

I suppose it might be a bit annoying though, if half the people on the plane were constantly chatting on the phone.  But, I suppose I haven't found cell phones to be too much of a problem on trains. CliffordK, Fri, 27th Jul 2012

You may be right Clifford. It comes down to marketing I think. The systems are based on the Iridium satellite system and they have, so far, laid out their stall for a relatively small market with high charges per kbyte of data. It seems they have sufficient capacity to handle more but they maybe concerned about how to offer cheaper rates without damaging their existing lucrative income. It is, to some extent, a chicken and egg situation. There is an upgrade coming in 2014 so we will see what happens then. graham.d, Mon, 13th Aug 2012

With respect to Dominic, as far as I know Boeing reached no such conclusion that use of mobiles on an aircraft was completely benign or that interference with systems has been exaggerated...

People trying to connect with cell sites as they are flying over them is not practical, even for the users let alone the network suppliers. The phones are trying to adapt their transceivers to rapidly changing sites with a rapidly changing multipath signal coming in through the gaps in the Faraday cage that is an aircraft hull. This often means that the transmit power would be ramped up to maximum; of course this will also be true of anyone trying to connect where therE are no cell sites (over oceans for example), and people would also try (and fail) to do this.

The only proper way is to install a pico-cell in the aircraft so that mobiles can use this with minimal power and a good connection. Commercial systems use this to then relay via the Iridium satellite network to maintain constant connections to various networks. Even this system is likely to be restricted during take-off and landing.

Of course there is the annoyance factor...

"I'm on a plane ... I said, I'M ON A PLANE"
graham.d, Thu, 16th Aug 2012

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