If you look at GPS notams, you will find a surprising number of area outages
that are small. They tend to be kind of conical in shape (small near the
ground and larger area as you increase in altitude. These seem to be due to
geometries for the satellite. If a satellite is out, this makes the
coverage even worse.

I fly in the east coast region (Wash DC ADIZ). There seems to be some areas
that have fairly permanent outage areas, perhaps jamming tests are done
there.

One should check GPS notams just as you would check VOR notams if you depend
on either navigation system.

Doug Wood

"Roger" wrote in message
news
On Fri, 5 Aug 2005 18:07:49 -0400, "Paul Lynch"
wrote:

A solar storm can render the GPS signals unusable for a period and
have at least once if not twice. It's a rare occurrence. OTOH it is
possible, but with a low probability of either meteor (dust size
particles), or a solar storm of enough magnitude, disabling a portion
of the satellite constellation.

Although the likely hood is very small, GPS is more likely to run into
a wide area failure than VORs. OTOH you can still fly via GPS with
only 2 satellites. With 3 it does a reasonable job of vertical nav.
I don't believe it'd be legal for approaches or you'd have enough
information for such, but it does show the *relative* immunity of GPS
to failures rendering the system unusable.

Both are good systems with GPS being far more accurate and less prone
to interference or failure.

GPS makes an excellent primary system, but as with any system for
serious work you always want a separate back-up. Your hardware can
fail, their hardware can fail, or some one could jam the system which
is true for any system. For emergencies even the old ADF and the
local AM broadcast station can get you in the vicinity of the airport.
It doesn't take much thinking to roll your own approach using an ADF
in an emergency.

If it's a true emergency you use what's available and sort out the
legalities later.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com
Ah figures lie and liars figure. Actually you are comparing statistical
apples and oranges.

If a single VOR fails in your area, or worse on your approach, you have a
little to a big problem depending on the circumstances. If a single
satellite fails for the area you are operating you are not likely to even
know it because so many other satellites are still available to provide no
worse than about 60M accuracy.

PK

"Jose" wrote in message
t...
No, it addresses the failure of a VOR and the failure of a GPS
satellite.

No, it doesn't =address= this, it =uses= this to =address= the original
point.

you're now comparing the failure of about 0.1 to 2% of the VOR system
to
the failure of about 69% of the GPS constellation.

... which is my point. A single VOR failure brings down 0.1% to 2% of
the
VOR system. A single failure brings down 69% of the GPS system. (your
numbers - I don't believe the 69% part and haven't verified the 0.1% to
2%
part though that sounds reasonable)

Jose
--
Quantum Mechanics is like this: God =does= play dice with the universe,
except there's no God, and there's no dice. And maybe there's no
universe.
for Email, make the obvious change in the address.