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19th July 2003, 02:07 AM

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.

19th July 2003, 02:07 AM	#2 (permalink)
joe Guest Posts: n/a Classified Rating: % ()	"GPS Unreliable" NOTAM 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.