How In-flight Mobile Phone Services Work

Before talking about in-flight mobile phone services, let's look at how cell phones work on the ground.

Despite its name, a cell phone is a two-way radio. However, it's more sophisticated than a citizen's band radio or walkie-talkie.

CB radios and walkie-talkies are simplex devices, meaning they use one channel to communicate. Because they use one channel, only one person can talk at a time.

A cell phone, however, is a duplex device. It switches back and forth between two frequencies -- one for talking, or transmitting; the other for listening, or receiving.

Will traditional cell phones work on planes? The New York Times reported that cell phones can be used in a flight's ascent and descent portions, but that their ability to work decreases as the plane climbs higher.

More airlines are adapting technology that allows passengers to use in-flight mobile services.

As of September 2007, Airbus passengers could make and receive phone calls and send text messages using their cell phones while flying at about 10,000 feet. The service cost passengers $2.50 a minute and 50 cents per message, the International Herald Tribune reported.

The service provider, OnAir, uses special equipment to route calls and messages through a satellite network, which patches it into the ground-based network. The airplane crew controls the system and can limit or disable its use.

Pico cell technology allows passengers to use their own cell phones on planes. Pico cells serve very small areas. In ground-based networks, they're used to serve areas such as a building's interior where signals are weak, or to boost network capacity. A Pico cell on a plane combines electronic equipment with an onboard antenna. The passengers' calls are sent to the central antenna and relayed to ground towers.

Even if in-flight cell phone service was available, it's not clear whether people would use it. A survey by travel management company Carlson Wagon-lit Travel showed that 61 percent of business travelers oppose using their phones in a plane. In response, airlines are looking at other ways to meet travelers' communications needs, such as high-speed Internet access.

AirCell helps U.S.-based airlines provide that service. The company's service allows passengers to surf the Internet, check e-mail and send attachments, as well as log into their office network from 35,000 feet.

More airlines, foreign and domestic, are pursuing this option, too.

The New York Times, in December 2007, reported some American airlines were offering in-flight Internet service. JetBlue Airways offers instant messaging while Virgin America and Alaska Airlines offer Web access. Experts predict in-flight Web access will be common within a few years.

American Airlines also announced it would test high-speed Internet service for its passengers in 2008 on its Boeing 767-200 aircraft, which primarily fly international routes. The technology will use three exterior antennas mounted on the aircraft. It will rely on a network of cell towers throughout the United States.

American Airline officials said the service is for their customers who rely on PDAs and laptops for real-time information and communications.

Even though wireless Web access could be used to make phone calls, most air carriers said they had no plans to allow voice communications. Airlines worried the chatter from cell phone users would annoy other travelers, while quietly browsing one's e-mail or surfing the Web wouldn't.

Besides an increase in chatter, what are the actual safety concerns with in-flight mobile phone services? Check out the next page to find out.

In the United States, both the Federal Aviation Administration and the Federal Communications Commission regulate the use of mobile phones on aircraft.

Safety concerns exist for both the cell networks and the airplane when traditional "terrestrial" cell phones are used in flight.

Because cell phones emit radio signals, government agencies worry that they can interfere with sensitive aviation electronics like communications equipment or the navigation system. Both of those systems rely on radio signals.

In the mid-1980s, when the first commercial cell phone networks began operating, the U.S. government adopted rules prohibiting their use onboard commercial flights. The rules were based on the above concerns.

On Sept. 11, passengers disregarded those rules when they called loved ones and law enforcement officials using both Airfone-type and traditional cell phone technology. Another safety concern, however, is that terrorists might use the signal from a cell phone to detonate an onboard bomb.

In spring 2007, the U.S. government decided to continue its ban on in-flight mobile phone use. An FAA spokesman said the agency was reacting to public fears that the signals given off by cell phone might interfere with plane controls.

Those fears might be well founded. The Telegraph reported that the British Civil Aviation Authority found up to 20 incidents between 2000 and 2005 where aircraft malfunction was related to mobile phone use.

Still, the European Aviation Safety Agency recently gave approval to OnAir to begin providing in-flight mobile phone service. The company's system uses phones that are less powerful than traditional cell phones aimed at avoiding such control interference.

Many European air carriers plan to use mobile phones in aircraft. But the topic remains controversial, according to the Telegraph article.

The FCC bans the use of cell phones using the common 800 megahertz frequency, as well as other wireless devices, because of potential interference with the wireless network on the ground. This interference happens as the planes, traveling several hundred miles per hour, leave one "cell" of mobile phone towers and enter a new one quickly.

The phones -- as well as any portable electronic devices such as iPods or portable radios -- also might interfere with the aircraft's navigation and communication systems. Therefore, the FCC bans their use during a flight.

Cell phones are a special concern in that they're specifically designed to send out signals strong enough to be received at a distance.

The FCC, however, has approved rules that allow in-flight voice and data services, such as broadband Web service, that use dedicated frequencies previously used by services such as Airfone.

An FAA fact sheet on the subject stated the agency's main fear is the unknown. The signals cell phones and other devices give off might effect critical aircraft systems over time. The FAA regulations prohibit most devices, though they specifically exempt voice recorders, hearing aids, heart pacemakers and a few others.

In general, however, the FAA advises airlines that most personal electronic devices are safe to operate over 10,000 feet. This is mainly because any potential interference would be a more serious problem at a lower altitude.

In some cell phones, users can operate in "airplane mode," which disables the phone's transmitter but enables the passenger to use other functions, such as its calendar or games.

Which airlines offer in-flight mobile phone service, and which offer limited service? Find out on the next page.

Air France started with a limited service trial in late 2007, allowing passengers to send and receive text messages and e-mails.

The airline planned to begin allowing voice calls within the first three months of 2008, but said it would regulate call makers "to maintain passengers' comfort and well-being," Network World reported.

Callers are allowed to use their phones only when the aircraft is 10,000 feet or higher off the ground.

Other airlines, especially those based in the United States, allow limited use of cell phones while on the ground. American Airlines and its subsidiaries, for example, allow use of cell phones during taxi-in, as signaled by an onboard announcement. Cell phone use is not allowed during flights, as doing so is against FCC rules.

However, several airlines are experimenting with a different cell-phone function -- using them as boarding passes. The International Air Transport Associations approved a method allowing airlines to send a barcode image to a passenger's cell phone in late 2007. The airline gate attendant can scan the image on the phone the same as one would scan a traditional paper board pass. With a projected 2010 start, advances such as these show that airlines and mobile phone technology will continue working together in the future [source: Into Mobile].

Along with such government rules, other issues, such as uncertain billing, customer service and service availability, keep airlines from providing full cell phone use onboard their aircraft in flight.

For lots more information about in-flight mobile phone service and related topics, check out the links on the next page.