[time-nuts] [OT] GPS from a window seat

Dave Baxter dave at uk-ar.co.uk
Fri Oct 2 08:19:14 UTC 2009

> Date: Thu, 1 Oct 2009 23:13:33 -0400
> From: "David I. Emery" <die at dieconsulting.com>
> Subject: Re: [time-nuts] GPS from a window seat
> 	I never had anyone from the airline bother me about doing this
> (discretely) UNTIL a recent flight this August from Boston to 
> London Heathrow on American ... when by chance my wife 
> fainted and passed out on the floor in the rear galley due to 
> a medication reaction and dehydration and naturally low blood 
> pressure (she is fine, and has been told this is very likely 
> harmless and it has happened before, but not on a plane)... 
> and they called a medical emergency and asked for a doctor to 
> help if one was aboard and very nearly diverted the plane to 
> Shannon thinking she had had a heart attack.

It's as much a "Catch All" policy, to prevent punters from using
cellphones on a plane.  Two reasons, they make money if there is an
in-flight phone service (that strangly only seems to work when flying in
US airspace.)  But there is a valid EMC reason too.

Tests were done a few years ago at London Gatwick, LGW (on the ground)
to see what impact (if any) the use of a cellphone had when used inside
a commercial pasenger aircraft.  I think a 737 was used, as "one was
available" but I'm not sure.  This was done with calibrated signal
sources and EMC measuring equipment.  I know this, as our company was
involved with the tests, though I wasn't personaly.

It was found, that wherever in the passenger cabbin the RF was launched
from, it often ended up concentrated in the avionics bay beneath the
pilots feet.  AFIK, with no effect to any engine or navigation systems
(I think they are very well engineered in EMC terms) but it did get into
the pilot/co-pilot intercom/headphones "quite noticably".

If you poke about the web, you should find the report, I believe it was
published a year or so after the test.

The thought of being in an aircraft being manually landed in a stiff
cross wind, and the pilot suddently getting a loud GSM rattle in his
ears, impresses me somewhat less.

Passenger aircraft will evolve to be immune to this, but most of the
current fleet were designed and specified way before the masses carried
cellphones, and most of the internal wiring is unscrened, and a lot of
it routes to/from the avionics bay I'm told..

On one "non" flight (we were stuck at Amsterdam Schipol, waiting for
snow to clear) we had a "gadget count" to pass the time.  I forget the
exact numbers, but there was well over 60% more phones on the plane than
people, and more laptop's/PDA than people too, just.

We were stuck there for so long (4 hours!) that we were passing phones
or batteries about so people could keep colegues/family informed, also
passing arround DVD's to those who had some life left in their laptop.

Have to say, the cabin crew were excelent, they couldnt do enough for
us, dispite the fact that we had been sealed up, pushed back, but gone
nowhere.  The flight crew too kept us informed above and beyond what
often happens.  We had to say on the 'plane, as the airport itself was
jammed with people.  And like most airports, even Amsterdam Schipol (a
"Huge" place) cant handle the welfare of that number of people stranded
for that sort of time.  I heard later from the Dutch office I had
visited, that it took over two days to get Schipol back on track when
the weather finaly cleared.

That "flight" end to end, was some 7 hours when I finaly walked out of
Luton (from when I was dropped of at Schipol.  I could have driven it
faster, thoug maybe not on that day with all the weather.)  The next
problem was the car park exit barier was frozen shut.  A bus driver was
less than subtle with his "fix" for that one..  ;-)


Dave (G0WBX)
Technical Manager, AR-UK Ltd  (Was EMV Ltd)

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