原创 Is it really safe to use cell phones during flight?

As I was doing some research on electromagnetic interference, I came across the information that the U.S. Federal Aviation Administration is loosening up on its ban on the use of mobile/cell phones and most personal electronics devices on aircraft.

Maybe I'm just a contrarian, but this is upsetting, to say the least. Although I have often been one of those airline passengers who resented being asked to turn off their electronic toys during critical stages of flight, I am not sure that lifting the ban, or even easing it up a bit, is a good idea.

The first thing that pushed me to re-evaluate my previous disgruntled position was what I read in the 2007 revised fourth edition of "EMC for product designers", by Tim Williams. It was his comments about the safe use of mobile devices on aircraft that caught my attention. Up to about 2007, he reports, tests in Europe indicated that at the GSM mobile frequencies it was possible to create the following interference effects (albeit with no affect on airplane safety in most cases):

*Compass freezing and overshooting of actual magnetic bearing;
*Instability of indicators;
*Display errors up to 5 degrees on digital VOR (VHF Omnidirectional Ranging) navigation bearing;
*Reversal of VOR navigation To/From indicators;
*Course deviation indicator errors with and without a failure flag on the VOR and ILS (Instrument Landing System);
*Background noise on aircraft audio outputs.

Particularly troubling to him at the time was the public reaction to the study. Although the interference was deemed unsafe and could have led to unsafe conditions, in these incidents no injury to passengers or pilots occurred. The public reaction was simple: because the interference did not cause problems in these specific instances, they were not relevant and the devices that produced the signals were safe to use on aircraft.

That was a few years ago, but troubling to me is that the FAA seems to have the same attitude today. In a recent FAA press release:

"Airlines can safely expand passenger use of Portable Electronic Devices (PEDs) during all phases of flight, and (the FAA) is immediately providing the airlines with implementation guidance. Due to differences among fleets and operations, the implementation will vary among airlines, but the agency expects many carriers will prove to the FAA that their planes allow passengers to safely use their devices in airplane mode, gate-to-gate, by the end of the year. The FAA based its decision on input from a group of experts that included representatives from the airlines, aviation manufacturers, passengers, pilots, flight attendants, and the mobile technology industry."

But one of the main studies the FAA seems to have relied on—Study on the Use of Cell Phones on Passenger Aircraft (DOT/FAA/AR-12/30)—is disappointing and is mostly a survey of what other equivalent organisations around the world are doing about this issue.

Where there is some specificity it is mostly anecdotal, with little detail. And the action they are taking is no action; that is, they are leaving it up to the individual airlines to make a decision based on how safe the use of such devices will be on their aircraft. The writers of the above report seemed to be more concerned with the safety aspects of passenger "air rage," when denied the use of their cells phones and PEDs.

I hope the specific information the FAA is requesting from the airlines is forthcoming. But until then, I am not convinced. Maybe the ban should be even stricter, especially considering the number of cell phones is approximately equal to the population of the earth and the number of electronic devices using a variety of wireless RF bands and methods is increasing. When I think about the mix of RF signals that will be swirling around the average IoT-enabled consumer in the future, my head spins!

Both for personal reasons (I ride airplanes) and professional (it is a technical issue that will have impact on the way such devices are designed and built), I am in the initial phases of doing research on this topic, despite the fact that everything I have read in the press indicates that the lifting of the ban is virtually a done deal.

Other than the FAA report, which was disturbingly light on any specifics, almost everything I have found so far with any technical meat on it is highly qualified in the conclusions and vague as to actions to be taken, other than recommending that more testing needs to be done.

A 2004 NASA report on "Portable Wireless LAN Device and Two Way Radio Threat Assessment for Aircraft," concluded that spurious emissions in the VHF-Com radio band from selected WLAN devices were lower than from laptop computers and PDAs, indicating that the WLAN devices tested are not any more threatening to the band than the common laptop computers and PDAs. But because of the many uncertainties about the results and the need for other more definitive tests, the study recommended a number of follow up actions, including:

1 - Additional receiver interference threshold data are needed for greater confidence level.
2 - More tests on a number of receivers from multiple manufacturers are recommended.
3 - Signal modulation and types should be considered.
4 – Need to conduct emission measurements and interference analysis on other types of wireless devices, particularly those utilising newly available RF bands and having multi-band capability.
5 – Need to assess the potential for emerging radio technologies that overlay existing spectrum (such as Ultra Wideband) to cause interference to aircraft systems.
6—Conduct additional IPL measurements on different types of aircraft where minimal data currently exists.
7—Assess impacts of multiple devices on EMI and aircraft safety.
8—Initiate flight operational assessment of PED electromagnetic interference (EMI) to aircraft radios, addressing safety impact of EMI as affected by navigation data processing and redundancy management within specific avionics packages, including the influence of crew and air traffic control procedures.

Another study, also done by NASA, but earlier, in 2003, titled "Wireless Phone Threat Assessment and New Wireless Technology Concerns for Aircraft Navigation Radios," reached similar qualified conclusions and recommended its own set of tests and evaluations to be made.

I am working my way through the references in both of these reports, as well as reading several other reports I have found. I am also looking for any indication that any of these recommendations were followed. But so far little has turned up that I consider useful or substantive. A lot of opinions but no hard data that I could trust. And little if anything later than 2003-2005, and a lot has changed in the almost ten years since then.

I hope that further research will prove me wrong, but based on the press comments I have seen, everyone seems to be in favour of the approval. Many rabid wireless phone and PED users want it. Device manufacturers seem to want it. Airlines, albeit with qualifications, want it. And politicians want it. However, many regular airline business travelers oppose it, but for reasons other than safety.

But given the proliferation of cell phones, mobile laptops, and PEDs now in use – and the potential for even more in the era of wireless IoT—I think we are owed some serious research into the safety question that is much less qualified in the conclusions reached.

One sign of hope is as that as of November 22 of this year, in an FAQ sheet published on the Federal Communications Commission web site, the FCC stated it "is seeking public comment on a proposed rule to allow airlines to expand access to mobile wireless services onboard aircraft, and will carefully review input from consumers and stakeholders before taking any final action."

If you are aware of some meaningful studies and tests that led to definite conclusions and recommendations, let me know and I will follow up. If you are especially knowledgeable in this area and would like to contribute what you know, please share your comments below.