The use of mobile phones on commercial aircraft is generally forbidden during flight. The most well-known reason for this banning is that the mobile phone could interfere with the sensitive equipment on the aircraft. This policy is often based around the fact that during development, many aircraft were not designed to accept signals from mobile phones and there has not been sufficient testing to be sure that they could. This basis can be seen in plans to improve certification [1]. However, the use of mobile phones on aircraft is forbidden across the board by most aviation regulators, and the design specifications of individual aircraft are not taken into account.
Social Resistance to Mobile Phone Use on Flights
Many people prefer the ban on mobile phone use in flight, fearing undue amounts of noise from cellphone chatter. People tend to talk more loudly into mobile phones than they do in person.
There are several reasons for this. One reason is people subconsciously rely on hearing their own voice back to modulate their own speech volume. Mobile phones don't send "backtalk" (a reduced volume "copy" of the person's speech) back into the earphone. Land-based phones have done this for a long time (this is also the cause of the "echo" effect you can hear on many cordless phones). Another reason is the conversation in the phone may demand more mental processing power. This is because mobile phones sound different from normal speech due to audio data compression or analog background noise. Whatever the reason, the net effect is the person is less aware of the people around him/her.
Electromagnetic Interference
Some level of electromagnetic interference is theoretically 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 the plane component in question. Whether that level of interference should have any influence on electronic systems which should be designed to fly through lightning storms without failing is often disputed by critics of the ban.
One area in which interference would be most likely is in the radio-based audio equipment used for voice communications between the aeroplane and the ground.
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. The high speed of air travel may make interference more likely than it would otherwise be. 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 analog cell phones broadcast at a higher power of up to several Watts. This has the potential to cause more general interference, and since the voice signal is not encoded there may be a concern of direct crosstalk into the communication system of the plane, although that is highly unlikely because the plane's radios transmit in an entirely different frequency band.
A recent study has shown that cell phones interfere with flight equipment. While not nearly as drastic as causing the plane to crash, cell phones can interfere with the intercom and possibly with voice communications. GSM phones most likely do this, because they can produce noise from nearby speakers. However, it would likely be legally unreasonable to ban certain cell phone providers (in the US, that would include Cingular and T-Mobile) while not others.
Current Situation
According to the BBC " most of the evidence is circumstantial and anecdotal. There is no absolute proof mobile phones are hazardous." [2] 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 [3]. A number of new phones have an "airplane mode" feature that presumably stops all incoming and outgoing communications while still allowing the user to play games, type notes etc.
A few U.S. airlines have announced plans ([4] and [5]) to allow mobile phones to be used on aircraft, pending approval by the FCC and the FAA. The idea is similar to that used in some cars on the German ICE train: the aircraft will contain a mobile signal repeater that will then transmit the signals to a terrestrial-based system on separate frequencies that do not interfere with the cellular system. Since the repeater is literally right next to the passengers, the phones' output power would be reduced to the lowest level possible, reducing interference with cells on the ground. ARINC and Telenor have formed a joint venture [6] company to offer such a service on-board commercial aircraft and will be launching a service in late 2006 that will safely allow you to use your cellphone on-board the aircraft. The cellphone calls are routed via the on-board SATCOM to the ground network and an on-board EMI screening system stops the cellphones contacting the ground network.