Originally Posted by
+TSRA
I've not seen it myself (yet), but I'm told it is happening during day flights on our network in the area of the US/Mexico border on tracks south of Phoenix, AZ, and east across to the TCS VOR. I'm told it's a very specific area that interestingly does not seem to extend into the San Diego area or when crossing into the Gulf east of Corpus Christi as those are both routes I've flown this past week and didn't see anything. I also did not see it a few weeks ago on two red-eye flights down to Costa Rica, but I'm told it happened on the return flight during the day. It's enough to make me wonder if it's an effect of some border operation - or if I'm having my chain pulled by an epic conspiracy.
The way the last guy I flew with described his experience, they noted the ANP slowly started to increase until they received the UNABLE REQD NAV PERF-RNP message on the FMC and the ND. They asked for appropriate traditional navigation clearances from ATC and then actioned the NNC. He said that just as they were getting to step 2, which has you enable radio updating, the ANP slowly started to come back down. They stopped the checklist and within a few minutes the ANP was back below RNP, and the UNABLE REQD NAV PERF-RNP message disappeared. All told he said it lasted about 5 to 10 minutes from when they first noticed the ANP climbing until it returned to within RNP limits.
That area is a known hotspot for GPS jamming and spoofing. The military does it frequently out of White Sands/Alamagordo and will be notam'd by ABQ/LAX/ ARTCC. Usually late night. The other known issue is cartels on the border, both used for stealing semis and spoofing CBP drones. I have had multiple jams, but no spoof yet. All but one were NOTAM. Navy will due the same off coast of California from time to time or at China Lake.