Date: 202010
Local time of day: 0001-0600
Location: ZDV.ARTCC, CO
Flight conditions: VMC
Weather elements / visibility: Turbulence
Aircraft: Widebody Transport
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Cruise
Airspace: Class A ZDV
ATC / advisory: Center ZDV
Reporter organization: Air Carrier
Reporter function: Pilot Flying; First Officer
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument
Second reporter function: Captain; Pilot Not Flying
Anomaly: Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Procedure
Primary problem: Procedure

Narrative: During operation of Aircraft X at FL340 we began having GPS navigational issues. Beginning in an area approximately 40 miles SE of ALS (Alamosa VOR) along our route to approximately 80 miles SW of RSK (Rattlesnake VOR); approximately 160-200 miles; we experienced intermittent 'GPS PRIMARY LOST' messages. As we began to troubleshoot the issue we discovered that both GPS #1 and #2 were erratically receiving GPS signals; varying from 0 to 9 satellites. The system cycled rather rapidly between the GPS 1 & 2 signal strength and navigational capability; losing all GPS capability at times.  We referred to the QRH but began to surmise that given the unusual operation of the receivers that there was nothing wrong with the onboard equipment and there must be an external issue like 'jamming'. We were discussing a plan: return to land base NAV and advise ATC or request ATC temporary headings when ATC asked if we were going direct to 'DAFNY'. We advised him that we were experiencing various NAV downgrades and asked for heading verification. He gave us a heading correction of 5 degrees left. Immediately after that transmission another aircraft reported the exact same issue with GPS NAV. After a few minutes the controller advised us that there were GPS jamming exercises going on in the area around White Sands. Therefore; we updated our heading with ATC as we progressed. A subsequent controller cleared us direct to 'ZZZZZ' and advised us we appeared to be slightly north of a direct route to 'DAFNY'. Shortly thereafter 'GPS PRIMARY' returned and normal operations ensued. We continued the arrival while checking our radar position with ATC. No further anomalies were encountered. Landed without further incident in ZZZ. I can only presume that the US Government (Military) was performing 'GPS Jamming' exercises as the controller said such activities were happening around the White Sands area. How about a NOTAM!


Second narrative: At FL340 we began to get several GPS Primary Lost indications. Navigation reliability was in question so we got vectors from ATC for the fix that we were cleared to. Multiple other aircraft in the vicinity were reporting the same issues with their GPS. ATC informed us there was 'jamming' going on at nearby White Sands. When our GPS finally seemed to be working again; we were several miles off course going to the assigned fix. We reported that our GPS seemed to be working again and we were cleared to a different fix. No further anomalies were encountered but I am writing this report because were were off course for a short amount of time. White Sands jamming of GPS reported by ATC.


Synopsis: Air carrier flight crew reported loss of GPS signal in cruise operations reportedly due to GPS jamming exercises.