Mobile phones on aircraft

The use of mobile telephones is generally forbidden aboard commercial aircraft during flight. In the European Union's airspace they are allowed

Technical issues

Channel reuse

The U.S. Federal Communications Commission prohibits the use of mobile telephones aboard any aircraft in flight. The reason given is that mobile phone systems depend on channel reuse, and operating a phone at altitude may violate the fundamental assumptions that allow channel reuse to work.

Mobile telephones are intentionally designed with low power output. A tower is the center of a "cell" and due to attenuation with distance (inverse square law) a phone can usually be received only weakly by towers in adjacent cells, and not at all in cells farther away (non-adjacent cells). This allows the channel used by any given phone to be reused by other phones in non-adjacent cells. This principle allows tens or hundreds of thousands of people to use their phones at the same time in a given metropolitan area while using only a limited number of channels.

Channel reuse works because from a mobile phone on the ground, there will only be one "closest" tower that can possibly use a particular group of frequencies, CDMA codes, or time slots. The software that manages the system assumes that the signal from a phone on a particular tower can, on other towers, only be "heard" at greatly reduced signal strength. The frequency, code, or time slot used by the phone can therefore be reused by other phones on other towers.

In the old analog cell system a channel was simply a frequency pair; there were seven groups of 35 channels each, and no two adjacent cells used the same channel groups. Modern CDMA and TDMA systems are more complex: A channel in TDMA is a frequency pair and a time slot, and a channel in CDMA is a spread spectrum key, but the principle of channel reuse still applies.

If a mobile phone is operated from an aircraft in flight above a city, this assumption is no longer valid, because the towers of many different cells may be about equidistant from the phone. Multiple towers might assume that the phone is under their control. The phone could be assigned a free channel by one tower, but could be heard on other towers using the same channel group, and the channel might already be in use on those towers. This could cause interference with existing calls. It is possible that the software controlling the towers could crash. Even if the software can cope with hearing the same phone on multiple, non-adjacent towers, the result at best is an overall decrease in the system's capacity.

An additional concern is the output power of the mobile handset. Because the towers might be many miles below the aircraft, the phone might have to transmit at its maximum power to be received. This will increase the risk of interference with electronic equipment on the aircraft.

To protect the integrity of the electronic control and navigation equipment aboard large airliners in commercial service, the use of cellphones designed for terrestrial service is forbidden. The FCC, however, did allocate spectrum in the 450 MHz and 800 MHz frequency bands for use by equipment designed and tested for safety for air-to-ground service, and these systems use widely separated ground stations. In the 450 MHz band, co-channel assignments are at least 497 miles apart, and in the 800 MHz band, only specific sites were authorized by the FCC. The 450 MHz service is limited to "general aviation" users (corporate jets mostly), while the 800 MHz spectrum can be used by airliners as well as general aviation. The 450 MHz is named AGRAS, while the 800 MHz service is under review following an auction of spectrum in 2006.

Electromagnetic interference

Some level of electromagnetic interference to aircraft systems is theoretically possible not only from active radio transmitters (such as mobile phones, small walkie-talkies, or radio remote-controlled toys), but also from unintentional emitters (such as ordinary radio receivers, computers, and in fact virtually any nontrivial electronic device).

There are some reports that support this, and some that refute it:

• Boeing performed extensive tests as reported in AeroMagazine's Interference from Electronic Devices in response to reports by flight crews of anomalies that they believed to be caused by electronic devices. The flight crews had apparently confirmed the effect by switching the "suspect" device on and off and watching the effects. Despite this, and despite the fact that Boeing in many cases was able to purchase the actual offending device from the passenger and use it in extensive testing, Boeing was never able to reproduce any of the anomalies. The report concludes:

As a result of these and other investigations, Boeing has not been able to find a definite correlation between PEDs and the associated reported airplane anomalies.

• ABC News 20/20 aired a report in December 2007 trying to get to the bottom of the ban on cell phone use on aircraft. They interviewed one of the authors of the IEEE Spectrum report cited below, but also noted that this study was not designed to actually detect interference, only that cellphones are not switched off sometimes. The report concludes that the primary reason for the ban on cell phone use in flight is that neither the FAA nor the FCC are willing to spend the money to perform conclusive safety tests. They have left this up to the airlines, who do not see any return on investment in paying for such tests. According to the 20/20 website, ABC News consultant and veteran airline pilot John J. Nance states categorically:

  There's little reason to worry about cell phones interfering with an airplane's navigational equipment. Nance says an airplane's electronic systems are "all heavily shielded. That means that stray signals cannot get into those systems."

• A NASA publication details the fifty most recent reports to the Aviation Safety Reporting System (ASRS) regarding "avionics problems that may result from the influence of passenger electronic devices." The nature of these reports varies widely. Some merely describe passengers' interactions with flight crews when asked to stop using an electronic device. Other reports in the set amount to crews reporting experiencing an anomaly at the same time a passenger was witnessed using a mobile phone, indicating only a weak correlation, not causality. However, a few reports state that anomalies were observed to appear and disappear as the suspect device was turned on and off, indicating a high degree of correlation.

• A NASA report from 2001 summarizes "14 years of incidents reported by pilots to the ASRS" of interference caused, or suspected to be caused, by passenger electronic devices. Mobile phones were the most frequently identified source of interference, with laptop computers a close second. In no cases were the affected avionics found to be defective upon later testing. Degrees of correlation or confidence were not among the data summarized in the report.

• A 2003 study involving three months of testing with RF spectrum analyzers and other instruments aboard regular commercial flights found that on a typical flight at least one mobile phone is likely to be left on throughout a typical flight, and that a mobile phone in use produces a far stronger signal than one that is simply left switched on. In the authors' words:

There is no smoking gun to this story: there is no definitive instance of an air accident known to have been caused by a passenger's use of an electronic device. Nonetheless, although it is impossible to say that such use has contributed to air accidents in the past, the data also make it impossible to rule it out completely. More important, the data support a conclusion that continued use of portable RF-emitting devices such as cellphones will, in all likelihood, someday cause an accident by interfering with critical cockpit instruments such as GPS receivers. This much is certain: there exists a greater potential for problems than was previously believed.

• A 2000 study by the British Civil Aviation Authority concluded that:

interference levels produced by a portable telephone, used near the flight deck or

avionics equipment bay, will exceed demonstrated susceptibility levels for equipment qualified to standards published prior to July 1984. Since equipment qualified to these standards are installed in older aircraft, and can be installed (and is known to be installed) in newly built aircraft, current policy for restricting the use of portable telephones on all aircraft will need to remain in force.. …For safety reasons, the Regulatory Authorities should continue to prohibit the use of portable

telephones by passengers on aircraft whilst the engines are running.

• A report from BBC news comments that "most of the evidence is circumstantial and anecdotal. There is no absolute proof mobile phones are hazardous." However, it quotes Dan Hawkes, head of avionic systems at the Civil Aviation Authority (CAA):

There's an industry consensus, throughout the world, that mobile phones are a potential hazard to aircraft and must be switched off. A typical aircraft these days could have anything up to 15 or more radio systems on board. The signals that a mobile phone gives out could penetrate into equipment, and could affect the operation of the computer. The computer may shut down, which would affect the aircraft's navigation, which in turn would affect the signals sent to the auto pilot, and the way the aircraft is automatically flown. The aircraft might go off course, and even might change height.

• Whether interference from small battery-powered devices should have any influence on electronic systems that should be designed to fly through lightning storms without failing is often disputed by critics of the ban. An article by Tekla S. Perry and Linda Geppert, then editors of IEEE Spectrum, offers an explanation: While a brand new aircraft may indeed be completely immune from such interference, shielding and other mechanisms that normally protect the avionics do degrade over time, after thousands of takeoffs, landings, and pressurization cycles and various maintentance procedures. Similarly, the shielding in passengers' devices also degrades due to the passage of time and, in some cases, repair procedures.

• While certainly not a rigorous scientific study, the Discovery Channel television program MythBusters examined the "myth" that mobile phones are banned aboard aircraft to force passengers to use the airline's inflight phones. They concluded that this is "busted." Their tests caused no interference to a small airplane's avionics, but did so to unshielded equipment. They concluded that interference could occur aboard an aircraft if the shielding was not working correctly.

Since the number of commercial aviation accidents from all causes each year is extremely low compared to the total number of flights, and mobile phones are indeed used in spite of the ban, it is clear that the risk of an accident stemming from present (illegal) use of mobile phones must be small. Weighing against this is that the cost of an accident, should one occur, could be extremely high in terms of human life, and that the risk is completely avoidable, in that no one absolutely needs to use their mobile phone in flight. The regulatory agencies and aviation industry understandably take the position that any increased risk is unacceptable if it is avoidable.

Some mobile phone systems, such as GSM may cause an irritating buzz (explained in the TDMA article), which could 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 airplane often exceeds these (typically phones are designed for use in a fast car) which means the phone will fail to register to the network and retry registration repeatedly.

Despite the FCC ban on the use of mobile telephones on aircraft, virtually every pilot headset sold on the market today comes with a cell phone adapter so that the pilot can use his cell phone through the headset. The manufacturers avoid legal responsibility by claiming the adapters are for use on the ground, but many general aviation pilots have used their cell phones in flight at one point or another.

Other factors

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 introduce adequate sidetone (a reduced volume "copy" of that person's speech) back into the earpiece. Landline 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 that the person is less aware of the people around him/her.

Also, one must not forget the very high level of background noise on an airplane which would invariably force people to talk even louder into their cell phones.

AT&T has suggested that in-flight mobile phone restrictions should remain in place, in the interest of reducing the nuisance to other passengers caused by someone talking loudly on a phone next to them. [2]

Competition for airlines' in-flight phone service

Some believe that the airlines support the ban because they don't want passengers to have an alternative to the in-flight phone service (such as GTE's Airphone). These services are much more expensive than mobile phone service. They also provide extremely slow data services at a similarly high price. In general, the airlines have had little success in selling these services, and the in-flight phone equipment has disappeared from most U.S. domestic flights.

Nevertheless it is apparently easy to believe that the airlines support a continued ban on mobile phone use so as to force customers to use the in-flight phone service. [3]

This idea is not supportable in light of the following:

• Use of all passenger electronic devices is banned by nearly all airlines during take-off, climbout, approach, and landing phases of flight (essentially whenver the aircraft is below 10,000 feet); and
• Mobile phones are not at all reliably usable at cruise speed and altitude.

The radiation pattern of the antennas on mobile phone towers intentionally causes strong attenuation at angles much above horizontal, and Doppler shift causes non-recoverable phase shift errors at high relative speeds between phone and tower.

Mobile phones therefore offer no real competition to the in-flight phone service.

Current regulations

United States

The use of cell phones aboard airborne planes is banned by the FCC in 47 C.F.R. § 22.925: "The use of cellular telephones while this aircraft is airborne is prohibited by FCC rules.... The use of cellular telephones while this aircraft is on the ground is subject to FAA regulations." This ban applies to phones that use the 800 MHz spectrum. PCS (Personal Communications Services) phones that use the 1900 MHz spectrum are governed under FCC 47CFR24, and their use in aircraft is not restricted by the FCC, whether on the ground or in flight.

The FAA, in 14 C.F.R § 91.21 bans the use of all portable electronic devices (with a few odd exceptions) for all flights operated by an airline or under IFR, but allows that the pilot (or airline) can make any exception to this rule if the operator deems that device safe. This effectively gives the operator (airline or pilot) the final word as to what devices may be used aboard an aircraft as far as the FAA is concerned, although the FCC restriction still applies.

No U.S. airlines have approved the use of mobile phones while in flight.

Note that for aircraft operated by an airline, the pilot is not considered the "operator" and cannot legally allow exceptions to the airline's restrictions, but the pilot may dictate additional restrictions.

The FAA, in Advisory Circular 91.21-1A recommends that aircraft operators blanket ban all intentional transmitters, mentioning specifically CB radios, remote control devices, and cellular phones. While Advisory Circulars are not legally binding, air carriers rarely ignore official written advice from the FAA.

However, this Advisory Circular has been superseded by AC 91.21.1B.

FAR 91.21 state that the Pilot In Command of an aircraft that is NOT IFR, and NOT Part 121 (Commercial Air Carriers), can allow usage of "Portable Electronic Devices". However, to take the attitude that "The FAA doesn't say I can't do it" is incorrect, particularly in the category of radiotelephone communications, governed by the FCC. FCC regulations, specifically Title 47 Part 22.925, (Oct 1, 2006 revision) states "Cellular telephones installed in or carried aboard airplanes, balloons or any other type of aircraft must not be operated while such aircraft are airborne (not touching the ground). When any aircraft leaves the ground, all cellular telephones on board that aircraft must be turned off.".

Possible future changes

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 would be very close to the passengers and inside the aircraft's metal shell the phones' output power could be reduced to the lowest level possible, reducing interference both with cells on the ground and with the flight-critical avionics. Such systems have been tested on a few flights within the United States, under waiver from the FCC.

ARINC and Telenor have formed a joint venture [6] company to offer such a service on board commercial aircraft. The mobile phone calls are routed via satellite to the ground network and an on-board EMI screening system stops the cellphones contacting the ground network.

These systems are comparatively easy to implement for customers in most of the world, where GSM phones operating on either of just two bands are the norm. The multitude of incompatible mobile phone systems in the United States and other countries makes the situation more difficult — it is not clear if the onboard repeaters will be compatible with all of the different cell-phone protocols (TDMA, GSM, CDMA, iDen) and their respective providers.

On 30 August 2006, the Irish low-cost airline Ryanair announced it will introduce a facility to allow passengers to use their mobile phones in-flight. [7]

As of mid April 2007 Qantas have teamed up with Panasonic Avionics Corporation and AeroMobile to commence a three month trial that will "enable customers to send and receive e-mails, access the Internet and send and receive text messages from their own mobile phone" [8]

On 18 October 2007 Ofcom published proposals for the technical and authorisation approach that would be adopted to allow this for European GSM users on the 1800Mz band on UK registered aircraft.

On 20 March 2008, Emirates Airline flights began allowing voice calls in-flight on some commercial airline flights.

The approval by EASA of these systems has established that GSM phones on certified aircraft types are considered safe to use when installed with a on-board cellular picocell.

26 March 2008, Ofcom of the UK has approved the use of mobile phone devices on aircrafts in UK and Europe. However the use will depend on the airline companies who will have to apply for licenses

See also

• Crossair Flight 498 - an alternate theory of the 2000 crash of this flight was based on the use of passenger cell phones, which resulted in a number of countries outlawing use of cell phones on flights.
• Mobile phone

External links

• Study: In-flight cell calls pose risk to planes
• 14 CFR § 91.21: The FAA rules regarding portable electronic devices
• 47 CFR § 22.925: FCC prohibition of airborne cell phone use, 1Oct2006
• Advisory Circular 91.21-1A: Use of portable electronic devices