Can you safely use a cellphone on an airliner?

 I researched and wrote this piece in 2006 but some of the issues it raises about using cellphones aboard aircraft are still unresolved.

Can we use our mobile on this flight?

Gerry Byrne

In June 1999 Neil Whitehouse, an oil worker of Mansfield, Notts, was sentenced to 12 months in prison after being found guilty of "recklessly and negligently" endangering a British Airways flight from Madrid to Manchester. He had neither a bomb, nor a gun but a mobile phone, or cellphone, on which he was texting "I Love You" and which he refused to switch off. When warned the phone could interfere with the aircraft's navigation he reportedly joked "Why? Are we going to get lost?"

Yet actions like Whitehouse's may no longer be a crime if trials of new technology aboard Air France airbusses prove successful. It is joining TAP Portugal and BMI in fitting new technology aboard aircraft which means passengers can make and receive calls on their own mobiles without risking an air disaster.

Concern about cellphone use first emerged in the early 1990s when a string of reports from aircraft crew said that difficulties with their instruments only ceased when passengers stopped using their phones. In the US the Federal Aviation Administration (FAA) banned their use aboard aircraft in 1991 while the Federal Communications Commission also banned them aboard aircraft because their use was interfering with base stations on the ground.

It has never been proved that flight or navigation anomalies were caused by cellphones and the mechanism by which interference from mobiles can interfere with flight instruments has never been conclusively demonstrated. Indeed the most persuasive tests of the impact of cellphones on flight instruments, when the UK Civil Aviation Authority created instrument anomalies aboard a jetliner, was conducted on the ground and has never been replicated in the air.

Cellphones are basically cleverly engineered two-way radios which route your phone call into a larger all-in-one local transmitter and receiver or "cell" which in turn is connected to the national landline and cellular phone system. As you move further away from your local "cell" your phone "registers" itself with a new, nearer, cell. In fact, mobile phones are constantly seeking out the strongest signal and will disconnect automatically from a weaker signal and attach themselves to a stronger one. They do this by means of an occasional pulse which is transmitted even if the phone is not in use.

"They are always saying "hello", I'm here", said Gerard Butler of Trinity College Dublin.

This creates the familiar beeping noise one often hears from a TV or computer speakers shortly before getting a mobile call and sometimes this can be heard, even when there is no call, because the phone is constantly seeking out the strongest signal. Pilots have reported hearing this sound on their headphones in flight and it was the co-incidence of hearing it, and simultaneously experiencing navigation errors or other instrumental anomalies, which first allowed them make the connection between mobile use and electromagnetic interference on the flight deck.

Mobile phones can transmit at varying power rates. Even when you are not making or receiving a call aboard an aircraft they can transmit at up to 2 watts, double the output of the average hand-held VHF walkie-talkie, when trying to reach a base station on earth.

At cruising altitude, a mobile phone's connection to a cell base station is weak and the phone automatically seeks out a stronger connection. On the ground the average mobile phone is usually in contact with, at most three base calls at any one time and will work only through one. In the air a phone can theoretically attempt to lock on to dozens and will be constantly pulsing as it attempts to decide which one is the strongest. Large numbers of phones left switched on in a cruising aircraft can create havoc with the cell phone system on the ground as all available channels are quickly clogged up.

"They have been successfully proved to interfere with aircraft instrumentation. It's less of an issue in some aircraft, which have better protection. But generally there have been problems with compasses and other navigation aids giving the wrong readings. Pilots can sometimes hear cell phones going off in their earphones, just like you can on your computer or TV, while the anomalies are occurring. We've done the research, there's definitely a link there," said Jonathan Nicholson, of the Civil Aviation Authority (CAA), the UK's aviation rulemaker.

Following ground based tests in 2002 using strong transmissions close to aircraft wiring, the CAA discovered dials giving incorrect readings, and compasses and other navigational aids freezing or overshooting.

But thanks to new technologies, there's now pressure on aviation authorities to relax the worldwide ban on cellphones. An example is the system designed by Tralee, Ireland based Altobridge which places a pico-cell, or transmitter-cum-receiver aboard the aircraft so that mobile phones can communicate with it at very low power.

"The presence of a nearby pico-cell aboard the aircraft effectively reduces the output of the mobile phone," said Guy Waugh of AltoBridge.

It then routes the conversation via established phone satellite networks, such as Inmarsat, the connections from which operate at flight-deck compatible frequencies, and at very low power. Honeywell has married its hardware with AltoBridge's software and says flight tests aboard a Cessna Citation business jet tests show there was no interference with the test aircraft's own systems. Related systems are also being tested by Norwegian telecoms giant Telinor and by Arinc, another telecommunications specialist.

The German Ministry of Transport has now proposed relaxing the in-flight mobile ban to allow the new technology while in the USA the Federal Communications Commission has already started a public consultation process to abolish its no-mobile regulation.

But even if the Germans relax the rule, it is hard to see how it can allow in-flight mobile use if other aviation authorities do not concur.

"Any rule changes have to be approved by the European Aviation Safety Agency," said the CAA's Nicholson. "There has to be majority voting; no single country can either force or veto a change."

A similar stand off may occur in the USA where, even if the FCC allows mobile use aboard aircraft, the FAA has said its ban is likely to remain in force. British pilots say they will continue to enforce the ban.

"We are being briefed about the systems that are on test but as far as we're concerned the rule remains switch them, off," said Keith Bill of the British Airline Pilots Association. "We are always going to remain on the safe side with this issue."

The problem remains that hitherto, there have been few reliable measurements taken in the air of interference from mobile phones and other potentially disruptive personal electronic devices (PEDs), like laptop computers and portable entertainment systems like DVD players and Ipods. (The latter are called unintentional transmitters). That changed recently following in-flight research by Granger Morgan and Bill Strauss and published recently in the USA in IEEE Transactions.

"Nobody ever measured the radio frequency environment in the cabins of working airliners in flight," said Morgan, department head of Engineering and Public Policy at the John Heinz School of Public Policy and Management at Carnegie Mellon University, Pittsburgh. "Ours was the first set of in-flight measurements ever made with passengers aboard. We carried a radio frequency probe on 38 revenue flights with two separate airlines and in a variety of aircraft. It had a broadband antenna and could scan various cellular and GPS bands. We were interested in the GPS frequencies because of reports from pilots that some phones affected the GPS navigation system. NASA has confirmed that aircraft often lost satellite lock."

The researchers detected emissions from phones which were left switched in clear breach of the FAA and the FCC rules. The probe also detected passengers making phone calls on take-off and on final approach.

"It is troubling because if picocells become more common you are going to see people using phones during all phases of the flight and not just in the cruise which is when the picocells are to be switched on," said Morgan.

"We scanned the navigation critical bands and found disturbing stuff," said Bill Strauss who conducted the Carnegie Mellon probes with Morgan. "The GPS region was quite active. NASA studies have found that some cellular phones emit in the GPS range. I can't prove if it was a phone but a lot of people were using them and a lot were left switched on. I cannot be sure if one contributed to the other but it adds a further dimension."

Concern is also caused by the unpredictable behaviour of radio transmissions in the close confines of an aircraft. "Multiple transmission sources can cause two signals to mix and create different frequencies," explained Morgan. "It's very messy and hard to reconstruct afterwards. It's very hard to work out why something happens in this area. One solution might be to attach a radio frequency probe to the black boxes aboard aircraft. I'd advocate taking it slowly until we understand what the problem is."

At Old Dominions University, Linda Vahala is preparing to model the behaviour of picocells within a fuselage. But, as she discovered during earlier NASA sponsored research, it will not be easy. Changing the location of empty seats can dramatically change the result, she found.

"We simulated the behaviour of mobile radio waves in different aircraft," she explained. "We have tried to reproduce certain tests but we never had the same conditions. I would advocate caution. There is the potential for interference in certain frequencies at certain places aboard the aircraft."

Earlier research at Old Dominions confirmed that apertures such as windows in an aircraft fuselage can actually amplify a signal as it leaves the aircraft so that it becomes even stronger as it re-enters it through a radio or satellite navigation antenna. She also discovered that the same signals can behave completely differently coming from a different seat, or if there are more, or less, passengers aboard.

Richard Lord of AltoBridge said his company anticipates that the pilots will switch off the pico cell until the aircraft is at 10,000 feet, not because of the danger of interference with instruments, but because airlines believe phone use in the cabin might distract cabin crew and interfere with safety announcements. However in those circumstance, Strauss believes that many passengers will try to use their mobiles despite the picocells being turned off.

"People will be less willing to believe that there are issues with interference if you install the picocell system," said Strauss. "Right now I believe most people assume that the reason for the ban is because airlines want people to use the more expensive seat back satellite phones."

Yet, even if the FCC once again approves mobile use aloft, there is no guarantee that the airlines will endorse it. According to Lufthansa, which has provided a satellite link aboard some aircraft so that that passengers can access their e-mail and the Internet, some people have been using internet phones and it has led to passenger complaints. "If we do allow mobile use it would have be in a quiet area, especially during long distance night flights," said a spokesperson.

British Airways has never trialled a voice system and says it will be customer led. If its customers are anything like the 7,000 respondents to the FCC's consultation process they might never allow mobiles. The vast majority of the FCCs submissions are opposed, not on safety grounds, but because the writers simply hate to hear people jabbering away on mobiles.

PANEL

In 2001 NASA researchers analysed the database of the Aviation Safety Reporting System which enables US pilots to anonymously report safety incidents without attracting an investigation or even disciplinary action. Between 1986 and 1999 it discovered 84 incidents, 39 of which were said to be critical, where the use of mobiles and other personal electronic devices such as mobile phones were linked to difficulties in flying the aircraft. Although many were reported to their airlines, in none of the reported cases were faults with equipment or wiring discovered by subsequent maintenance efforts. They were divided almost equally between advanced and less advanced cockpit designs.

About 44% occurred during a critical phase of flight, such as taking off and climbing, or descent, approach and landing. Some 31% occurred below 10,000 feet. A quarter of the anomalies were detected by ATC. In many cases the aircraft strayed off course although the cabin instruments suggested that they were flying correctly. In a quarter of the off-course cases, it was alert traffic controllers who spotted the aircraft's dilemma. In a small number of other cases, pilots also claimed that flight controls were affected, mostly autopilots, and radio communications were also affected.

One pilot reported that, in 1995, while making an automatic landing using the autopilot, the system indicated that the aircraft was on track but the pilots could plainly see that they had drifted well to the left of the runway and that the autopilots had disconnected. The same year another pilot reported an uncommanded drop of 300 feet in altitude and that the speedbrakes, flaps on the wings to slow airspeed, were suddenly extended. A year later another report showed false reading on the flight deck and the aircraft suddenly pitched down and lost 500 feet in altitude while attempting a landing. A 1999 report of navigation system malfunctions reads: "tone in headsets (confirmed NOKIA mobile phone)."

Out of 65 critical anomalies identified in the survey, mobile phones and laptops were equally implicated with 16 and 15 cases respectively identified. In nine cases the PED was never identified but others implicated included electronic games, radios, tape recorders and players, CD players, movie players, portable TVs, calculators and pagers.