Why the FAA May Finally Relax In-Flight Device Rules

Nick Bilton at the New York Times has been writing skeptically for years about the FAA's ban on even the most benign electronic devices during takeoff and landing on commercial passenger flights. He writes in the NYT's Bits column about the gradual transformation that may (real soon now) result in slightly more sensible rules; a committee established to review some of those in-flight rules has recommended the FAA ease up, at least on devices with no plausible negative effect on navigation. From the article: "The New York Times employed EMT Labs, an independent testing facility in Mountain View, Calif., to see if a Kindle actually gave off enough electromagnetic emissions to affect a plane. The findings: An Amazon Kindle emitted less than 30 microvolts per meter when in use. That is only 0.00003 of a volt. A Boeing 747 must withstand 200 volts per square meter. That is millions of Kindles packed into each square meter of the plane. Still, the F.A.A. said “No.” ... But then something started to change: society." Of course, the rules that committees recommend aren't always the ones that prevail on the ground or in the sky.

Hope the committee has a better grasp of units

[Anonymous Coward]

Withstand 200V per square meter? If that's not just a typo, we are talking about a change in magnetic flow density. 30uV/m, in contrast, is an electric field strength. The electric field around any battery is much larger than that, but nobody wants to prohibit carrying batteries around. You don't get any magnetic flow from that, but you can get magnetic flow from a change in electric field change. In fact, depending on the frequency of the change, the change in magnetic flow density can get arbitrarily large even when we are talking about an amplitude of just 30uV/m.

Journalistic pseudo-science

[Anonymous Coward]

There may well be solid technical arguments for reversing the current FAA policy, but Nick Bilton's articles certainly don't make them. Nor does the explanation attributed to the EMT Labs engineers, at least if it was described accurately. On the other hand, statements like "An Amazon Kindle emitted less than 30 microvolts per meter when in use. That is only 0.00003 of a volt" are clearly designed to make what sounds like a convincing argument to non-scientists, whether or not this argument actually has any technical merit.

As an illustration: the nominal signal strength of a GPS signal at the antenna of a receiver is specified to be -160 dBW (this is for a standard "reference" antenna, i.e. right-hand circularly polarized, under open sky conditions). That's one-ten-thousandth of one-one-millionth of one-one-millionth of a watt. In a standard 50-ohm RF system, this corresponds to a voltage of about 0.000000071, which is over four hundred times smaller (weaker) than the "only 0.00003 of a volt" signal measured off the Kindle. Viewed in that light, it's hardly clear that the Kindle's emissions are negligible. (Never mind the fact that no mention whatsoever is made of what frequency or frequencies they've measured in that setup, and that the anechoic chamber pictured in the article is typically configured to measure direct line-of-sight field strength, whereas inside an aircraft there are all sorts of complicated effects -- absorption by passengers and seats, reflection by metal surfaces, etc. So I'm not sure this is even a meaningful measurement to be making in the first place.) In any case, since GPS is considered a safety-of-life system in aircraft navigation, anything that can even come close to disrupting its ability to acquire and track signals is a potential problem.

The bottom line is that the kind of pseudo-scientific argumentation in this article isn't really helpful. As I said, there may well be sound technical reasons to relax the devices ban. But this doesn't really present any of them.

-CF

Re:Like the reporter has a clue...

[pepty]

I always thought the issue wasn't properly functioning cell phones, kindles, walkmen, etc interfering with VOR or HF bands (the rules predate GPS on phones) ; the problem was electronic gadgets that generated lots of RF interference due to malfunction or due to being cheap imports that were never UL approved in the first place. Airlines could test everyone's electronics for interference during or right after boarding ... or just make everyone turn every damn thing off. I know which is simpler and faster.

Re:Like the reporter has a clue...

[thygate]

In many radio reception techniques the signal is down-converted to a much lower frequency for easier processing. This is done through so called "heterodyning", which takes the carrier signal and mixes it with the signal from a Local Oscillator (LO) to create an Intermediate Frequency (IF). The IF and LO signals will radiate and need to be properly shielded.

Re:Like the reporter has a clue...

[Mr. Freeman]

That sounded really good until you mentioned that GPS receivers could compromise the plane's GPS. You didn't just shoot yourself in the foot, you blew your entire God damn leg off. GPS receivers RECEIVE GPS signals and don't emit anything. They also don't use heterodyne, so don't try and play that card. You sounded like you knew what you were talking about, but clearly you don't.