Signal failures: Efforts to ensure that avionics are immune to electromagnetic interference intensify

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This story is sourced from Flight International
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Whether or not personal electronic devices (PEDs) can interfere with avionics in the cockpit has been debated for years. Even though regulators have never traced the cause of an aircraft accident to interference from PEDs, the topic continues to grab headlines as more travellers bring smartphones, tablet computers and other wi-fi devices on board, and some airlines look to turn popular tablets, such as the Apple iPad, into electronic flight bags (EFBs) with real-time applications.

The issue of electromagnetic avionics interference was catapulted into the spotlight this year when it emerged that Honeywell Phase 3 liquid crystal display units installed on certain Boeing 737NG and 777 aircraft had proved susceptible to blanking when subjected to intense EMI tests on the ground.

Such tests are a requirement for obtaining supplemental type certification (STC) of in-flight wi-fi and mobile connectivity solutions. Blanking is understood to have been specifically observed when STC was sought for Gogo's wi-fi system on American Airlines' 737NG aircraft. While Boeing and Honeywell concluded actual EMI levels experienced during normal operation of typical passenger wi-fi systems would not cause a problem, the issue was deemed serious enough for the US airframer to suspend line-fitting connectivity systems to its 777s, a decision that impacted several international airline customers of mobile connectivity provider AeroMobile.

in flight telephony, onair
 © OnAir
OnAir's systems are supported by Inmarsat's SwiftBroadband

Boeing also initiated a broad avionics review to ensure no other products are susceptible to interference, and began drafting a service bulletin to address the Honeywell issue.

The discovery that Honeywell Phase 3 displays are susceptible to EMI put the industry on high alert over interference issues as airlines move to retrofit their fleets with passenger communications systems. Stakeholders are moving forward with a heightened sense of awareness about the importance of ensuring aircraft are tolerant to PEDs, including transmitting PEDs or T-PEDs.

"A number of vendors are sticking stuff on aircraft through STC, and the STC is specific to a particular aircraft model. It's tied to the airframe and not the avionics and, as you know, it's very, very difficult to get two exact aircraft with the exact same avionics suite with the same versions installed, so you definitely have the opportunity to see [EMI interference] again if testing is not done right or is done loosely or not complete," Ken Bantoft, vice-president of engineering at consultancy Satcom Integration, says.

When conducting EMI tests for STC, applicants are required to perform a ground test using a portable wireless transmitter emulator. RTCA/DO-294B defines a test procedure with an emulator consisting of a signal generator, amplifier and transmitting antenna.

TAKING PRECAUTIONS

"The emulator antenna should be placed at each location, including the flight deck, in the airplane cabin where the access point antennas are installed, and at locations where WLAN-equipped PEDs may be operated," says the Federal Aviation Administration. "Monitor all aircraft systems with catastrophic, hazardous, and major failure conditions, and systems required by certification or operating regulations."

While this published guidance has been available for several years, the FAA appears to be paying closer attention to whether these tests are being performed as directed.

"For wi-fi testing, you use a four-watt transmitter and you move it around in the aircraft. That's massive in terms of power instead of your standard wi-fi access point that is about 125Mw. But while the tests specify a four-watt transmitter, some folks have done it with less and the local FAA has signed off on it," a source claims. "Now, because of the visibility this issue is hitting, the FAA is ensuring a four-watt transmitter is used."

Another source says any bolstered scrutiny by the FAA is borne out of concern terrorists might focus an intense amount of radio frequency (RF) power at the flight deck, and less to do with whether a multitude of T-PEDs in the cabin can cause temporary blanking of screens. Adding some credence to the argument, perhaps, is the fact the industry has known for years that many passengers do not shut off their devices during critical phases of flight - including take-off and landing - yet flight attendants are not required to inspect each passenger's PED for compliance.

A captain who flies a Gogo-equipped aircraft for a US operator tells Flight International: "I guarantee that every single flight there are at least a couple dozen devices that are 'on' from taxi to take-off to cruise to landing to taxiing in. I've never ever seen any evidence that a personal electronic device has any effect on navigation communication or displays. You could have a ham radio in the back and it wouldn't affect us."

Furthermore, says the pilot: "There are many times I've forgotten to turn off my own iPhone and I've observed no in-flight abnormality whatsoever. This is one pilot that basically pooh-poohs the idea that these airplanes need to be hardened further, because I believe they are shielded enough today." Nonetheless, regulators and airframers are erring on the side of caution. "People ignoring the instructions to turn the device off doesn't change the instruction to turn the device off, and doesn't change the physics at all," Boeing associate technical fellow Dave Carson says. "You want to make sure you do everything you can to make sure safety or navigation systems on an airplane are unimpeded."

Guidance released last year by the FAA describes an acceptable means for designing and demonstrating aircraft tolerance to potential electromagnetic interference from PEDs. The FAA advisory circular AC 20-164 identified RTCA/DO-307, which goes further than RTCA/DO-294B, says Carson, who co-chaired the committee that developed DO-307.

SERVICE BULLETIN

The document provides test methods to verify avionic system RF immunity for intentional transmitting PEDs and to verify interference path loss for PED spurious RF emissions. If the guidance is successfully completed, the aircraft is deemed tolerant in all phases of flight, says Carson. Indeed, when Boeing and Honeywell set out to find if blanking of Honeywell Phase 3 displays on 737NGs could occur, they subjected the units to testing procedures specified in DO-307.

Boeing previously said a service bulletin to address the issue was imminent but now says it is likely to be delayed until next year and is directing questions to the FAA. However, sources say the bulletin is expected to mirror conditions in the STC, which requires operators to place placards in cockpits disallowing crew from using cabin connectivity on the flight deck, among other requirements.

"Anytime you're dealing with cockpit stuff, it's glacial. What they try to do is change as little as possible because the more you change, the more certification work you're going to end up doing, so what I'd imagine they're doing is trying small tweaks that so far haven't worked. They'll finally sort it and then fix it."

Carriers adhering to European Aviation Safety Agency protocol, meanwhile, follow the European equivalent of DO-307, known as ED-130. "When we manage STCs, we must demonstrate to the airworthiness authority that the system does not create a risk," says Veronique Blanc, chief technical officer of OnAir, an Airbus/SITA joint venture whose in-flight mobile and internet systems are supported by Inmarsat's SwiftBroadband.

Pico cell technology on each aircraft suppresses power transmissions from mobile phones on board.

WI-FI CONNECTIVITY

"When it comes to connectivity systems, in particular passenger mobile phones, when the [OnAir] system is not [turned on] then you potentially have a scenario where a lot of passengers' phones are transmitting at potentially high power. D0-307 and ED-130 are essentially the same, and you have to make sure critical aircraft systems are not immune to RF signal," notes Blanc.

All of the STCs managed by OnAir have, however, included placards disallowing the use of mobile phones in the cockpit.

"It's not the outcome of any particular interference. OnAir's focus is very much on cabin services - Mobile OnAir and Internet OnAir," she says.

However, OnAir does work with third parties to integrate other applications, such as EFBs, telemedicine and live news updates, into the system over the SwiftBroadband pipe, adds Blanc. OnAir is line-fit offerable on Airbus' portfolio of aircraft. OnAir's competitor, AeroMobile's largest customer Emirates uses placards in its 777 cockpits. The carrier, like several others, has been working with Boeing to ensure connectivity is again offered line-fit by the US airframer.

Sources say that since Boeing has internally decided to move in the direction of placards, airlines will soon start seeing 777s being delivered with wi-fi connectivity. However, mobile connectivity may take a little longer, as the FAA is understood to be taking an active role in how certification for the GSM mobile phone system is performed.