Business & GA, Commercial, Military

Wireless Cabin: All Issues Resolved?

By James W. Ramsey | January 1, 2004

The wireless aircraft cabin is already here, according to some experts. Or the technology is on course and closing fast, according to others.

But key issues–including interference with cockpit electronics–remain unresolved, driving operators and regulators to search for solutions. Many experts think that the hurdles will be surmounted. Air travelers eventually may be using not only wireless Internet services, but portable electronic devices (PEDs), including cell phones, on aircraft in flight. Wireless Internet access is offered in business jets now and will be operational on two European airlines next spring. Of all PEDs, mobile phones are probably the biggest concern for airlines because of their "unintentional" emissions in avionics bands and because of their power levels, which typically are higher than those of other unintentional transmitters, such as laptops, experts say.

The estimated time for approving all of these devices ranges from six months, at the most optimistic, to two years, says Rob Brookler, a spokesman for the World Airline Entertainment Association (WAEA). Issues involving cell phones and cell phone technologies, however, "will probably be pending quite a bit longer than for an all-enclosed 802.11b standard wireless Internet connection," he concedes.

Yet even e-mail and Internet access could pose some problems, Federal Aviation Administration (FAA) officials say. "We’re thinking about the electrical issues, interference issues, security issues–we don’t want somebody to come on board with a laptop that has a virus, and suddenly you can’t fly the plane because there’s been some problem," says Steve Van Trees, Avionics Systems Branch manager in FAA’s Aircraft Certification Service.

Both of the next-generation aircraft–the proposed Boeing 7E7 and the Airbus A380–have separate certification proposals for onboard wireless local area networks (LANs). FAA’s Certification Service is responsible for approving cabin installations on those aircraft and others, ensuring that they don’t interfere with aircraft systems.

The agency also is charged with ensuring continued airworthiness maintenance requirements "to make sure the system keeps working as it is supposed to when it was installed," explains Tim Shaver, an FAA transportation industry analyst reporting to Van Trees.

"One of the challenges when you certify a plane is that you deal with a certain electrical profile of the back cabin, and then people decide to bring cell phones and PDAs [personal digital assistants]–and then the whole electrical profile changes," Van Trees states.

"You have control over aircraft parts, but you don’t have any control over the person’s laptop in Seat 22A," Shaver adds. "You don’t know if the person is taking the laptop apart to put in more memory and accidentally removes the EMI [electromagnetic interference] shielding from the hard drive."

"If you look at our law, there are only five specific things you can use on board–voice recorders, hearing aids, pacemakers, electric shavers and any other PEDs that the operator has determined will not cause interference with the nav or com systems on the aircraft," Van Trees explains.

Interference Issue

To deal with these issues, RTCA Inc., at FAA’s request, established in May 2003 Special Committee 202 (SC-202) to study whether wireless telecommunications devices on commercial flights interfere with avionics equipment. The committee also works closely with other groups, such as the U.S. Federal Communications Commission (FCC), other RTCA panels, a European working group on PEDs–EUROCAE Working Group 58–and the Aging Transport Systems Rulemaking Advisory Committee (ATSRAC). SC-202 also is to define standards that the airline community–manufacturers, service providers and others–could apply.

PED emission standards today are in place to ensure that the devices don’t interfere with each other in an office environment, explains Kent Horton, Delta Air Lines’ general manager of avionics engineering and SC-202 member. "The PED standards are not necessarily set [to ensure] the devices won’t interfere with aircraft."

In January 2004, SC-202 is scheduled to complete Phase 1 of its research to establish guidelines relating to the use of PEDs in aircraft. The Phase 1 research, resulting in a guidance document for regulatory authorities, covers the impact to onboard systems of current technologies, such as analog and digital cellular phones, wireless PDAs, and devices with IEEE 802.11a, IEEE 802.11b and Bluetooth wireless network capabilities. Phase 2, scheduled to be completed in October 2005, will cover future technologies, such as ultra-wideband (UWB) devices or pico-cells for telephone use on board aircraft.

The two guidance documents are to "provide means for aviation regulatory authorities, aircraft operators, aircraft manufacturers, PED manufacturers, and others as appropriate, to determine acceptable and enforceable policies for passenger and crew use of portable electronic devices," according to an SC-202 document.

In a parallel effort to that of SC-202, WAEA has established a Wireless Working Group (WWG), whose charter is to "advance the use of wireless devices–cell phones, PDAs, computer LANs, and entertainment devices–on board and in the traveling environment." The WWG nonetheless is concerned with how these devices may affect aircraft operations. "Airlines want to safely offer their passengers onboard access to the same tools these travelers depend on at home," says Rich Salter, WAEA Technology Committee co-chair.

"What SC-202 does is collect a whole series of results from our experts and industry experts on what the testing profiles look like," Van Trees says. Shaver, who represents FAA headquarters on the committee, has examined "to what extent onboard aft cabin equipment can interfere with how many GPS satellites the pilot can see," Van Trees adds. As the noise floor (interference level) from these devices is raised, "what is the degradation of the navigational systems’ operation because of this interference?"

Daunting Task

SC-202’s task is daunting. One of the problems is trying to understand or model the actual interference signal. "Because of differences in devices, it is hard to pick a representative group of devices, take them on an airplane, and then simulate the way they are going to work," says Shaver. (Cockpit systems that RTCA is concerned about include an array of critical elements such as air traffic control [ATC] transponders, DME, satcom, traffic alert collision avoidance system [TCAS], GPS, UHF/VHF communications, the ILS localizer and glide slope, and VOR.) GPS and satcom already operate with narrow susceptibility margins.

Delta’s Horton agrees with the complexity of the task. "This [PED] equipment has to fit a footprint or a specification or some emission standard, generally on the part of the FCC in the U.S., and other standards around the world. There is some variability there we aren’t used to dealing with in the avionics realm," he says.

"The difficulty is, the evidence escapes at the speed of light," Horton says. "The emission that is causing the problem–as soon as the device powers down–is gone. It’s very difficult to prove and repeat." There are many variables beyond a device’s emissions that make interference events hard to evaluate and interference effects difficult to recreate in a controlled environment. These include changes in the strength or frequency of the intentional avionics signal, the location of the airplane, the atmospheric conditions, the possible interaction of signals from multiple sources inside and outside of the aircraft, and even the orientation of the portable device.

In one case about two years ago Delta was able to obtain and test a mobile phone that had been linked to an interference incident on one of its aircraft. But when the airline tried to recreate the same conditions in a test scenario, it was unable to duplicate the interference effect.

While the work done so far by fellow SC-202 committee members has been valuable, there are other challenges presented by onboard PEDs, acknowledges Bill Winfrey, specialist-advanced technologies for Delta and SC-202 co-chairman (with Boeing Commercial Airplanes’ David Carson). For example, pico-cells could allow cell phone use in the aircraft at any time. Basically, they provide the "handshake" that connects the airborne caller with the ground phone network.

But onboard cell phone use "is not as straightforward as one might think and can be a complex issue," according to Winfrey. "The problem now could well be [with] the mix of digital phones and analog phones–the latter phones require a lot more energy," he explains. "And how does a flight attendant tell one guy he can use his digital phone and tell the guy across the aisle that he can’t use his analog phone. And can the flight attendant even tell the difference in phones? It becomes very complicated."

The big problem with cell phones is their unintentional emissions, which do fall in avionics radio bands. "You don’t need much energy coming from a cell phone or wireless LAN to upset the radios," says Chuck LaBerge, an SC-202 member and senior principal engineer with Honeywell’s Communications and Surveillance Center of Excellence. SC-202 is trying to assess whether PEDs can operate on the airplane without interfering with the avionics and still provide the avionics some margin of safety, he says. Damaged phones are also an issue because they may no longer operate as intended. "In my opinion, something will have to change" with mobile phones for them to become approved for use in flight, he says.

Another major challenge, according to Winfrey, is the rapid change in PED products. "It used to be a Game Boy was a Game Boy, and you knew what it was and what it did," he says. "Now we have telephones that are also cameras and devices in which a passenger can communicate with someone 12 rows ahead or 12 rows behind."

SC-202’s Phase 1 study also includes investigation into wireless LANs. Delta, for one, is assessing the possibility of using a wireless LAN in its aircraft and feels it would benefit "the staff that operates the airplane," as well as the passengers, Horton says. A wireless LAN could carry information relating to passengers, sales and catering. Delta, however, has no active program to provide a wireless link, Horton says.

Going wireless minimizes aircraft downtime for system installation. But "a concern out there with a lot of folks is [that] you’re vulnerable to somebody monitoring that data," Horton says. Someone on the ground could set up an antenna to monitor the radio frequency transmissions. Or a passenger with a laptop could capture wireless information onboard the airplane. "So you have to be aware of security issues, whereas in the wired environment you don’t normally have that security issue."

Current Rules

Current FCC regulations prohibit the use of analog cell phones on aircraft–a regulation intended primarily to prevent interference from an airborne cell phone with ground-based mobile phone service. And while the FAA rule allows PEDs at the operator’s discretion, their operation is prohibited completely during takeoff and landing. FAA refers to the airlines’ prohibition as the "10-minute, 10,000-foot limit."

"Today, when you get on an airplane, you turn off the cell phones and other devices when the door closes, and you can’t use them until the aircraft is 10 minutes out and at or above 10,000-foot altitude," says Van Trees. "Once they [the airlines] did this, complaints of [EMI] interference from pilots dropped off dramatically. We figured 10 minutes was the right number."

"Current policies today essentially state that intentional transmitters are not allowed on aircraft at all unless proven to be safe, and only then in certain phases of flight," explains Joe Keegan, cabin systems technical center manager for Boeing. "There is a difference in FCC rules, between analog and digital cellular [phones] on aircraft. The original rules were designed to prohibit analog-type cell phones. The newer rules allow PCS [personal communications system]-type phones on aircraft." But how can airlines tell the devices apart?

Keegan believes that the wireless LAN systems (operating on 802.11b-type technology), such as Connexion by Boeing is utilizing on Lufthansa and SAS, have a "pretty fair path to getting [to certification on aircraft]." These systems are "pretty discreet in terms of their transmission characteristics," he explains. "It’s fairly straightforward to show that those technologies, by themselves, are non-interfering.

"But if you expand the scope to other intentional transmitters–like cell phones–you get a lot more complex, because now you have many different standards of technology over many frequency ranges. We’ve studied interference for all those technologies, but admittedly have only scratched the surface."

Keegan summarizes Boeing’s philosophy on these issues by saying: "Our primary concern is safety of the aircraft. And if we’re not absolutely sure that something is non-interfering with that, then we just won’t allow it ourselves, or we’ll support the policies of the industry."

Avionics Manufacturers

Avionics manufacturers also are members of SC-202. "We’re worried that everybody’s going to take [the additional interference] out of our hide," out of our noise budget, says Honeywell’s LaBerge.

"We’re not against new services, but the aircraft environment is very different from the commercial office environment that the PED folks are used to." There are dozens of antennas on a commercial airliner, LaBerge explains, and "they are all open ports into the [avionics] radios." There’s a limit to how much protection can be provided if unintentional emissions occur on the channel that a sensitive avionics radio is trying to receive.

There’s a precedent for this concern, LaBerge says. Regulators in the mid-1980s required the airline industry to replace localizer/VOR receivers with ones that were more immune to FM broadcasting interference. They did replace them and "it cost a bundle," he says. "They don’t want to do that again."

NASA Research

Delta and United Airlines also are working with NASA Langley to look at "mitigating procedures" to help prevent interference incidents. These include better crew training, identification of the devices with greatest interference potential, helping to define acceptable emissions standards and trying to convince PED manufacturers to build in features such as an annunciation when the device is in a mode that has been identified as unacceptable for in-flight use.

The work has improved understanding of interference mechanics, Horton says. "So far we’ve taken a lot of data on our fleet of aircraft to understand, at least on paper, what the vulnerabilities and sensitivity thresholds are." In 2004 he expects measurements of aircraft to be taken to see how the aircraft handles a signal emanating from a cell phone or other PED.

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