The use of mobile phones is generally disallowed on aircraft during flight. One reason given for this is that the mobile phone could interfere with the sensitive equipment on the aircraft. This could be restated as "during development these aircraft were not designed to accept signals from mobile phones and there has not been sufficient testing to be sure that they could" as can be seen from plans to improve certification [2] (http://www.caa.co.uk/docs/389/srg_sys_00002-01-300103.pdf). It is clear, however, that there is some level of interference is possible from active radio transmitters such as mobile phones on aircraft. Exactly how much and in what way is dependent on the particular phone system in use and which component of the plane we are discussing. Whether that level of interference should have any influence on electronic systems which should be designed to fly through lightning storms without falling out of the sky is an entirely different question.
One area in which interference is likely is in the radio based audio equipment used for communicating from the aeroplane to the ground. The mobile phone transmitter will be much closer to the receiver on the aircraft; this means that any cross talk from the mobile phone will have a strong effect.
Some mobile phone systems such as GSM may cause an irritating buzz (explained in the TDMA article) which would certainly disrupt communications from the pilot to ground. Unfortunately, the conditions on an aeroplane are exactly those which might cause this. The maximum speed of travel in a mobile phone system is limited by several factors, frequency changes, rate of change of timing offset, etc. The speed of an aeroplane often exceeds these (typically phones are designed for use in a fast car) which means the mobile will fail to register to the network and retry registration repeatedly.
Older analogue systems simply broadcast at a high power of up to several watts. This will cause more general interference, and since the voice signal is not encoded there may be direct cross talk into the communication systems of the plane.
Another factor is that from an altitude, distant cells are visible to the mobile with no line-of-sight attenuation from intervening obstacles. This means that the phone could try to establish contact with a far away cell where the signal will not be recognised. This transmission will probably be at maximum power due to the lack of prior response. The U.S. Federal Communications Commission prohibits the use of mobile phones in the air for this reason. This repeated sending of maximum power messages increases the risk of interference with electronic equipment on the aircraft.
Having said all the above, according to the BBC "most of the evidence is circumstantial and anecdotal. There is no absolute proof mobile phones are hazardous." [3] (http://news.bbc.co.uk/2/hi/uk_news/399154.stm) Some airlines do allow use of mobiles phones in flight, only restricting their use (and use of all other electronic devices) during take off and landing when communications with the ground are most critical. Meanwhile the passenger aircraft manufacturers, such as Boeing and Airbus, have begun to introduce wireless services on their planes (e.g. WLAN) and radio based satellite phones are a standard installation on aeroplanes. Clearly there is a direct airline industry advantage in having control over communication systems from within an aeroplane, with no clear way for potential competitors to certify their systems as safe for use on board. Some articles have even gone so far as to accuse the airline industry of pushing the ban on mobile phones in order to increase revenue from on board telephones.
Rrticle originally published on http://en.wikipedia.org
