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Friday, December 17, 2010

Mobile phones on aircraft


Mobile phones on aircraft

Mobile phones on aircraft are strictly regulated as concerns exist that mobile phones pose a danger to the aircraft and passengers. It is thought they could adversely affect the navigational instruments in the cockpit and so such devices must be turned off while the aircraft is airborne.
The use of mobile phones and similar devices has been banned by regulatory bodies such as the United States' Federal Aviation Administration and others across the world. Many reasons have been given and tests have been performed to try and identify any possible interference that may arise from their usage in–flight. The general conclusions are that any risk that may cause aircraft failure and passenger deaths is too high until testing confirms that the risks have been dealt with or do not exist.
The major problems are that the mobile phones or other electronic devices may interfere with aircraft systems or computers due to poor or missing shielding and so cause a catastrophic failure of the control mechanisms. There have been few instances where a definite link between device use and system failures have been proven and in those cases where a correlation has been shown it has tended to be where shielding was in fact not present, of bad quality or had been compromised.
Since the regulations were imposed by the various international bodies there have been advances in equipment and systems which have allowed the gradual introduction of safe in-flight communications via mobile phones and such devices. These systems are being implemented by an increasing number of airlines and carriers as each is tested by the authority responsible for air-safety and deemed to be fit for use.

Mobile phone usage issues

Electromagnetic interference
Electromagnetic interference to aircraft systems is theoretically possible from active radio transmitters such as mobile phones, small walkie–talkies or radio remote–controlled toys and also from unintentional emitters such as ordinary radio receivers, computers and virtually any non–trivial electronic device. However, there has been little empirical support of this theory and studies have either been non-conclusive or found there there is no evidence that use of electronic devices on could interfere with an aircraft's systems.
There are some reports that indicate 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" devices 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 usage in 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 which are not switched off. 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 made 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 amount to crews reporting an anomaly experienced at the same time a passenger was witnessed using a mobile phone which indicates only a weak correlation and not causality. However a few reports state that anomalies were observed to appear and disappear as the suspect device was turned on and off which would indicate 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 passengers 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 involved three months of testing with RF spectrum analyzers and other instruments aboard regular commercial flights. The report found that on a typical flight at least one mobile phone is likely to be left on throughout the 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." It also quotes Dan Hawkes the 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 to unshielded equipment. They concluded that interference could occur aboard an aircraft if the shielding was not working correctly.

Conclusions
The cost of an accident, should one occur, could be extremely high in terms of human life and the risk is completely avoidable in that no one absolutely needs to use their mobile phone in flight. The regulatory agencies and aviation industry 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, 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. and the speed of an airplane often exceeds these as, typically, mobile phones are designed for use in a fast car which means the phone will fail to register to the network and retry registration repeatedly.

Other factors

Social resistance to mobile phone use on flights
People may prefer a ban on Mobile phone use in flight as it prevents undue amounts of noise from cellphone chatter. For several reasons people tend to talk more loudly into Mobile phone than they do when talking in person.
AT&T has suggested that in-flight mobile phone restrictions should remain in place in the interests of reducing the nuisance to other passengers caused by someone talking loudly on a phone next to them.

Competition for airlines' in-flight phone service
Skeptics of the ban believe that the airlines support the ban because they do not 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 services. They also provide extremely slow data rates 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.
It could be 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 with comments such as those made by Andy Plews a spokesman for UAL's United Airlines. "We don't believe it's a good safety issue"..."We'd like people to use the air phones."

Current status

Emirates Airline
On 20 March 2008, Emirates Airline flights began allowing in-flight voice calls 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 an on-board cellular picocell.

Europe
AeroMobile and OnAir allow the use of personal electronics devices aboard flights. The services are most prevalent in Europe and are licensed to specific airlines for use.

Malaysia Airlines
Malaysia Airlines flights are installed with AeroMobile systems to enable in flight voice calls and text messages.

Mobile phone on corporate jets
Falcon 2000 on 2 April 2009 implemented a new concept designated SafeCell when it commenced flying.

United States
To prevent disruption to the cell phone network from the effects of fast-moving cell phones at altitude (see discussion below), the FCC has banned the use of cell phones on all aircraft in flight. The FCC did, however, allocate spectra in the 450 MHz and 800 MHz frequency bands for use by equipment designed and tested as "safe 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, in corporate jets mostly, while the 800 MHz spectrum can be used by airliners as well as for general aviation. The 450 MHz spectrum is named AGRAS while the 800 MHz service is under review following an auction of the spectrum in 2006.

Regulations and practices
Mobile phones are portable electronic devices and, as such, are banned from use in civilian airplanes by the Federal Aviation Agency unless the operator of a commercial aircraft or pilot of a private aircraft determines that it could not cause interference to avionics in the aircraft.
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 those flights under Instrument flight rules (IFR). It does allow that the airline (or for privately operated aircraft the pilot) can make an exception to this rule if the operator deems that device safe. This effectively gives the 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.
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 although the pilot may dictate additional restrictions.
No U.S. airlines have approved the use of mobile phones while in flight.
The FAA in Advisory Circular 91.21-1A recommends that aircraft operators blanket ban all intentional transmitters and mentions specifically CB radios, remote control devices and cellular phones. While Advisory Circulars are not legally binding air carriers rarely ignore the official written advice from the FAA.
This Advisory Circular has since been superseded by AC 91.21.1B.
Federal Avaiation Regulation (FAR) 91.21 states 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, and 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 an aircraft leaves the ground, all cellular telephones on board that aircraft must be turned off.".
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. Personal Communications Services (PCS) 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.

Cell tower channel re-use
The U.S. Federal Communications Commission (FCC) currently 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.
The FCC is also concerned that the use, or even non-use, of a powered cell phone could cause disruption to the cell systems' towers and has banned their use.
Mobile telephones are intentionally designed with a low power output. A tower is the center of a "cell" and due to attenuation with distance (inverse square law) cell phone transmissions 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 a mobile phone on the ground will only have 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 these assumptions ares no longer valid because the towers of numerous different cells may be about equidistant from the phone. Multiple towers might assume that the phone is under their control and the phone could be assigned a free channel by one tower but could also be heard on other towers using the same channel group. The channel might already be in use on those other towers and could cause interference with existing calls. It is also 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 system capacity.
An additional concern is the output power of the mobile handset. Because the towers might be 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.

Recent and future changes

In flight technology
Airlines have installed technologies to allow phones to be connected within the airplane as it flies. Such systems were tested on flying scheduled flights from 2006 and in 2008 several airlines started to allow in-flight use of mobile phones. These changes have been attributed to strong demand by frequent fliers. A few airlines that are installing the equipment are also considering the issue of "phone-free zones" and "quiet time" on long flights.

Future changes
A few U.S. airlines have announced plans to allow Mobile phone to be used on aircraft pending approval by the FCC and the FAA. The method is similar to that used in some cars on the German ICE train and the aircraft will contain a device known as a picocell. The picocell will act as a miniature mobile telephone tower communicating with mobile phones within the aircraft and relaying the signals to either satellites or a terrestrial-based system. The picocell will be designed and maintained for full compatibility with the rest of the on-board avionics. Communication between the picocell and the rest of the telephone network will be on separate frequencies that do not interfere with either the cellular system or the aircraft's avionics much like the on–board phone systems already aboard many commercial aircraft. Since the picocell's antennas within the aircraft would be very close to the passengers and inside the aircraft's metal shell both the picocell's and the phones' output power could be reduced to very low levels reducing the chance for interference. Such systems have been tested on a few flights within the United States under a waiver from the FCC.
ARINC and Telenor have formed a joint venture 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. This service as started on the 19th February 2009 with 20 of their Dublin based aircraft.
As of mid April 2007 Qantas teamed up with Panasonic Avionics Corporation and AeroMobile to commence a three month trial that would "enable customers to send and receive e-mails, access the Internet and send and receive text messages from their own mobile phone"
On 18 October 2007 Ofcom published proposals for the technical and authorisational approach that would be adopted to allow this for European GSM users on the 1800Mz band on UK registered aircraft. and on 26 March 2008 Ofcom approved the use of mobile phone-supporting picocells aboard aircraft in the United Kingdom. Airline companies will have to equip the aircraft with picocells and apply for licences.

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 the use of cell phones on flights.
Ansett New Zealand Flight 703 – There is speculation that cell phone interference with the radio altimeter while on instrument approach may have caused this crash although the official accident report cites the cause as pilot error and states "The aircraft manufacturer’s avionics representative advised that there was no likelihood that the operation of a computer, other electronic device or a cell phone would have affected the aircraft’s flight instruments."


(source:wikipedia)

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