"GPS Unreliable" NOTAM

"Richard Kaplan" <rkaplan@flyimc.com> wrote in message
news:R71Sa.10708$7O.7886@nwrdny01.gnilink.net...

>
> If my plane had nothing but GPS-based avionics, what would my
> options be?
>

Vectors.

Richard Kaplan wrote:

> The recent thread regarding GPS as the sole navaid sometime in the future
> has focused on terrorism as the "what if" scenario.
>
> I am not focusing specifically on terrorism in my concern re: the need for
> GPS redundancy; I am simply observing that there is no system or device I am
> aware of anywhere in aviation which works 100% of the time, so certainly it
> is always worh having a backup. Even if GPS has 12 satellites, it seems
> clear by common sense that the best backup system would use a technology
> different from GPS.
>
> With that as background, look at the following NOTAM, which is currently
> available on DUAT. We can theorize all we want about whether this NOTAM
> exists due to military testing or some atmospheric irregularity or whatever,
> but the point is that the NOTAM really is out there and will be effective in
> a few days. If my plane had nothing but GPS-based avionics, what would my
> options be?
>
> GPS 07/015 ZDC GPS UNRELIABLE WITHIN A 100 NM RADIUS OF PATUXENT
> VORTAC (PXT) AT 10,000 MSL THROUGH FL400, AND DECREASING IN AREA
> WITH DECREASE IN ALTITUDE TO 80 NM RADIUS AT 4000 FT AGL
> 1200-2000 DLY WEF 0307211200-0307252000
>

Again, there are toy airplanes then there are real airplanes. All high-end jets
have triple IRUs feeding position to the FMS and LNAV. So, if the primary nav
sensor shoots craps around Podunk, Merrykanasa, you just coast along using
triple-mized inertial position until the GPS kicks back in.

joe@obilivan.net wrote:

>
> sensor shoots craps around Podunk, Merrykanasa, you just coast along using
> triple-mized inertial position until the GPS kicks back in.

Make that triple-mixed.

> > > If my plane had nothing but GPS-based avionics, what would my
> > > options be?
> >
> > Vectors.

Ray Andraka <ray@andraka.com> wrote:
> Doesn't leave you any out should comm go down. I've had that
> happen due to P-static, ice on the antenna, and problems with the
> radio in a rental.

Now you're theorizing about a simultaneous double system failure -- GPS
and communications. It's impossible, just extremely unlikely.

You can keep adding redundency to get the probability of incapacitation
as low as you want, but eventually an event will happen which will take
out all of your backups at the same time. What's the odds of a DC-10
having all three hydraulic system fail at the same time? They said it
was impossible, yet it happened (Souix City, uncontained failure of a
turbine disk).

By far the most likely cause of simultaneous GPS and COMM failure is
loss of ship's electrical power. It would take out your VOR, ILS,
Loran, too. The way to protect against that is multiple electrical
busses (like in twins), or battery backup and/or handheld devices.

I wrote:
> It's impossible, just extremely unlikely.

Obviously, that's a typo. It should read "It's NOT impossible".

"Ray Andraka" <ray@andraka.com> wrote in message
news:3F18C4DD.E7430BF5@andraka.com...
> Doesn't leave you any out should comm go down. I've had that
> happen due to P-static, ice on the antenna, and problems with the
> radio in a rental.
>

Dial in last good frequency or 121.5 on the handheld.

"Richard Kaplan" <rkaplan@flyimc.com> wrote:
> Clearly this situation is absurd, and for that reason we cannot and never
> will switch to GPS-only navigation.

Is anybody saying that we should?

"Richard Kaplan" <rkaplan@flyimc.com> wrote in message news:R71Sa.10708$7O.7886@nwrdny01.gnilink.net...

> With that as background, look at the following NOTAM, which is currently
> available on DUAT. We can theorize all we want about whether this NOTAM
> exists due to military testing or some atmospheric irregularity or whatever,
> but the point is that the NOTAM really is out there and will be effective in
> a few days. If my plane had nothing but GPS-based avionics, what would my
> options be?
>
From my discussions with some stationed there, it is airborne GPS jamming testing.

Well, you still can't get HIWAS on a GPS. I suppose if GPS ever became the
sole navigation system we would have to depend on downloaded weather.