[time-nuts] Boeing 787 GPS reception trouble
woody at pch.net
Mon Jun 2 15:18:00 EDT 2014
I'm posting this from inside an Ethiopian 787, on the ground, with the doors closed. I just completed a fifteen-minute voice call initiated from inside the plane, with reasonable reception and no drops, while the doors were open. And I was able to get a new GPS location in less than two seconds (though that wasn't from cold boot, so I don't know whether it was able to accelerate the process using cached data previously received). The phone (an iPhone 5S) is showing three bars inside the plane, and was varying between three and four bars outside. Note that the non-linear mapping of signal strength to "bars" is a matter of intense negotiation between carriers and vendors, and shouldn't be taken as a literal indicator of anything at all. Likewise, Ethiopian may have ordered planes with significantly different options than ANA (no center overhead storage in business, for example) and used different paint formulation.
Nevertheless, in this specific case, I'm not seeing anything that seems out-of-the-ordinary relative to other aircraft.
> On Jun 2, 2014, at 10:03, "Tom Van Baak" <tvb at LeapSecond.com> wrote:
> 1) When I fly I often use my iPhone while on the ground, before take-off or after landing.
> 2) I sometimes carry a GPS receiver. When permitted (varies by airline), it's fun to log NMEA data for a flight and later plot the flight path and duration with UTC accuracy.
> 3) On occasion I also bring a logging Geiger counter. It's amazing how much background radiation there is up at flight altitude compared to down at ground level. You can go from 10 or 20 CPM (counts per minute) at home to, say, 500! CPM at 40k feet. Those of you who live in mile-high Colorado enjoy higher background levels. I know, because my Geiger counter was wonderfully close to 60 CPM (= 1 CPS) in a hotel near NIST. Yes, I have the 1PPS ADEV plot for this and, yes, background radiation makes the world's worst "atomic" clock.
> Anyway, over the years I've collected some nice GPS latitude/longitude/altitude data sets as well as background radiation as a function of altitude. Just to be clear, I do turn off these devices according to airline regulations.
> Now I have never had a problem with reception in the terminal, walkway, or even while seated inside a plane. I figured the aluminum frame of the plane was thin enough that photons at cell, GPS, and gamma frequencies easily pass through the outer shell or the windows.
> But last week I flew the new composite Boeing 787 Dreamliner and noticed something quite different. From the second I entered the plane, I lost both cell and GPS reception. It didn't matter how close I was to a window or not. I know the word "composite" sounds inert, but carbon fiber must be somewhat conductive, yes? And there must be serious lightning suppression layers too, maybe? Furthermore, the B787 windows are exotic; like giant oval LCD screens which electronically dim from near transparent to very opaque. Does all this make the new 787 a record-holding RF-tight flying Faraday cage?
> Is this the first airplane in history where a time-nut can't receive GPS? At least gamma rays make it though, so I got RAD data. But no GPS data. Not a single SV fix the entire time I was inside the plane.
> Has anyone else noticed this? Or know about this? Please respond only if you have real information. I can speculate as well as anyone; so it's solid technical, RF, EMF, or composite carbon fiber engineering info I'm looking for.
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