[time-nuts] GPS from a window seat

David I. Emery die at dieconsulting.com
Fri Oct 2 03:13:33 UTC 2009

On Thu, Oct 01, 2009 at 08:21:28AM -0500, Bill Hawkins wrote:
> Group,
> I'll be flying around the world from Minnesota, USA, to Kuala Lumpur,
> Malaysia, to give a talk on industrial process control.
> Bought a Garmin 60CSx handheld GPS so I could tell precisely when I
> crossed the date line (a man's gotta have some goal in life).
> Is this feasible? Can you see enough satellites from an airliner window
> while crossing the Pacific from Los Angeles to Singapore? What side
> would work better, N or S?

	I have been doing this on and off for years with a now very
antique Garmin IQUE-3600.... not the most sensitive handheld GPS by any
means but if one holds it with the patch antenna facing the window and
tilted up - from a a window seat - it will lock and work fine.   I am
sure it is deaf enough so it won't possibly work from other than right
by the window.   It usually doesn't lock inside buildings even near a

	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.

	I was sitting with my teen aged son in coach and my wife across
the aisle  and down a seat and didn't realize she was the one in trouble
- just that she had gotten up to ask for a glass of water and gone back
to the rear galley - so when I heard the PA announcement about the
medical emergency I fired up the Garmin to see where we were (about 600
miles off the coast of Ireland) and when the chief purser came a couple
of minutes later to ask me if it was my wife and what medical conditions
she had he spotted me with the GPS and chewed me out (practically before
telling me about my wife's situation) saying angrily "using a GPS on a
plane is illegal".   I checked the AA magazine on the way back to the US
a week later and it was completely silent on GPSes... not listed as
allowed and not listed as forbidden - but I was sitting in the middle seat
of the middle aisle so I had zero chance to even think about trying the
GPS in any case.

	I do not recall ever seeing a specific prohibition, though
vaguely defined "radio receivers" are often banned on some airlines.

	Before my VERY frightening episode this summer, the only other
times I've had any notice from the cabin attendants is maybe one nod
to put it away when portable electronic devices are supposed to be
off and stowed.

	I am unaware of any general prohibition on GPS use on airliners...
I thought I followed this enough so if there were one I'd have heard of
it, but I haven't.   Of course individual airlines have wide latitude to
set their own rules (and decide whether to enforce them).

	I have, in fact, used the GPS on the way to and from China over
the Pacific and it worked fine... it sometimes takes quite a while for
that antique to lock up when in motion at 650 MPH.... and I have had 
intervals when it didn't find 3 or 4 SVs it could lock on from where
I was holding it... usually moving it around a bit would cure this,
especially using its signal strength screen to optimize this.

	I carry and use the thing because I have hated for years to fly
along looking out the window and not be sure what I was seeing when an
interesting lake or coastline or island or city goes by... having the
zoomed out world maps to see this is nice... helps one learn geography
and geology... and something about air traffic routing.   Most airline
passenger displays tell you roughly where you are, but rarely show
enough info to recognize specific landmarks and land features... and
what that highway is...

	Perhaps the most fun with the thing was riding across France on
the TGV bullet train and watching it hit 195 MPH on the GPS...  for an
American that was FAST for a train...
	A final note is that I am sure (though I haven't tried) that it
should be easy to detect the 1090 MHz Mode S ADS-B GPS position beacons
with a simple MMIC LNA and diode detector and time stamping box (which
exist now as a hobby item with a USB interface) and a laptop to decode
and display the positions on a map.  I can't believe that quite a bit of
RF from the radar/mode S ATC transponder doesn't get into the cabin and
the digital messages aren't currently encrypted and do contain the
plane's position and course and altitude.   Not all planes run ADS-B but
it is the future of ATC.

  Dave Emery N1PRE/AE, die at dieconsulting.com  DIE Consulting, Weston, Mass 02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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