Air carrier flight crew reported experiencing GPS jamming in the vicinity of SJN VORTAC.
Synopsis
Air carrier flight crew reported experiencing GPS jamming in the vicinity of SJN VORTAC.
Narrative
Suspected GPS Jamming:We experienced GPS jamming around SJN VOR. ANP (Actual Navigation Performance) on our Nav display went from 0.3 to about 2.0 over about a 20 minute period (slow onset); at first; we saw EICAS messages: ATC FAULT; and then about 10-15 minutes in: UNABLE RNP; and TERR SYS UNAVAIL (not entirely sure on last message). QRH directed us to use NAV/RAD INHIBIT ON; and the ANP went back down to 0.3 and the NAV/RAD INHIBIT message cleared but ATC FAULT remained for full 20 minutes. Right around that 15-20 minute mark; we started hearing some other airplane complain of GPS jamming; and then ATC mention that there was some 'GPS jamming exercises' that night . Now I cannot recall where it was; does SJN vortac around NM and AZ but cannot completely say with confidence. We reported to ATC right after our message cleared that we had also experienced jamming; but they never specifically notified us about jamming in our area. Due to onset of fatigue and other flight duties; I neglected to realize this was an FOM reportable event; and did not make an AML (Aircraft Maintenance Logbook) entry after the fact. Incidentally; FO and I called in fatigued after this leg due to inability to before this flight and inability to nap before the next flight.Cause: Suspected GPS jamming caused by military exercise. Suggestions: Better reporting from nearby enroute facility; such as ATC could have alerted us to it. If Dispatch had known; they might have given us a different route.
Second reporter narrative
Suspected GPS Jamming:We experienced GPS jamming around SJN VOR. ANP (Actual Navigation Performance) on our Nav display went from 0.3 to about2.0 over about a 20 minute period (slow onset); at first; we saw EICAS messages: ATC FAULT; and then about 10-15 minutes in:UNABLE RNP; and TERR (Terrain) SYS UNAVAIL (not entirely sure on last message). QRH directed us to use NAV/RAD (Radio) INHIBIT ON; and theANP went back down to 0.3 and the NAV/RAD INHIBIT message cleared but ATC FAULT remained for full 20 minutes. Right around that 15-20 minute mark; we started hearing some other airplane complain of GPS jamming; and then ATC mention that there was some GPS jamming exercises" that night. Now I cannot recall where it was; with SJN VORTAC being around NM and AZ; but I cannot completely say with confidence. We reported to ATC right after our message cleared that we had also experienced jamming; but they never specifically notified us about jamming in our area.Due to onset of fatigue and other flight duties; I neglected to realize this was an FOM reportable event; and did not make an AML (Aircraft Maintenance Logbook) entry after the fact. Incidentally; FO and I called in fatigued after this leg due to inability to [nap] before this flight and inability to nap before the next flight.Cause: GPS jamming.Suggestions: ATC notice."
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.