Not sure if this is the right spot for this but what the heck.
This NOTAM is why they still say you should have something besides GPS in the cockpit.
A0010/08 (GPS 01/021) - QXXXX GPS IS UNRELIABLE AND MAY BE UNAVAILABLE WITHIN A 324 NM RADIUS OF 372023.4N/1160158.4W (LOCATED WITHIN THE TONOPAH TEST RANGE) AT FL400, DECREASING IN AREA WITH DECREASE IN ALTITUDE TO 277 NM RADIUS AT FL250, 198 NM RADIUS AT 10,000 FT MSL AND 197 NM RADIUS AT 4,000 FT AGL. THE IMPACT AREA ALSO EXTENDS INTO THE MEXICAN FIR. F/G) SEE TEXT. 1900-0845 DLY, 21 JAN 19:00 2008 UNTIL 26 JAN 08:45 2008. CREATED: 11 JAN 18:00 2008
I experienced an un-NOTAM’d GPS outage a few months ago. There were a few other airplanes who reported problems too. Pretty odd. First thing I noticed was the airplane started to make turns right and left. I looked down at the data and saw a 150kt crosswind shift to a 4 knot tailwind to 70kt crosswind from the other direction. I guess while we were losing satellites the data was getting corrupted, causing a position error which the autopilot was attempting to correct for.
Eventually the GPS went offline completely and the FMS reverted to DME/DME positioning. We monitored, but never had to switch completely to raw data (green needles) from the VORs.
I’m surprised it didn’t go DME/DME as soon as you lost RAIM. We never have a problem when we go through GPS dithering areas… Our FMS-6100’s are configured by Collins to use DME/DME primary and then GPS, except when flying an RNP RNAV procedure.
