[time-nuts] Boeing 787 GPS reception trouble

Poul-Henning Kamp phk at phk.freebsd.dk
Mon Jun 2 05:27:44 EDT 2014


In message <BB41DBA7E336413BB9D643DF4D4F613D at pc52>, "Tom Van Baak" writes:

>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.

Only for short tau.  It should be pretty good at tau > 1e3 years or so ?

>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.

This is by design, so the plane can contain its own in-flight
wireless services.

WLAN in planes is no problem, there is a subset of channels which are
almost globally safe to use.

However, the next big cash-cow is supposed to be inflight mobile
phone + data, and bringing a Mobile Femtocell into any country
you might happen to fly over is a regulatory violation and paperwork
nightmare.

Originally the GSM spec had a sort of "RFC1918" facility, were one
specific frequency would be "local space", for exactly this kind of
application on marine vehicles.  Your phone would never automatically
roam to such a net, you'd have to explicitly select that a 'local space'
base-station, and you'd be stuck to it, until you manually released it.

However, given governments gold-hunt in spectrum allocations, that feature
died in the crib, and has not subsequently been revived.

Therefore airlines and cruise boats have to use regulated frequencies
if they want to offer cell-service.

Cruise-boats use a loophole in the international maritime treaties,
even when in harbour, they're under their national flag, and since
most of them are Bahamas or similar, getting a mobile license and
frequency allocation is cheap.  (Usually they crank up the power
when in harbour and milk any unsuspecting land-locked tourists with
exorbitant roaming-charges.)

Planes are not similarly "nationalized" and apart from the aeronautical
spectrum, they cannot emit any radiation for which they are not
licensed by the country they overfly.

And so they've started to build the planes as farady-cages.

It would be trivial to add a passive GPS repeater to the plane, but
the airtraffic industry has never been happy about people being
able to receive navigation signals inside planes, worrying that
somebody might try to blow up the plane at some specific place
(or non-place), so that ain't gonna happen.


-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.


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