Narrative:

Enroute while in oceanic airspace we got a message on the navigation display 'unable reqd navigation perf rnp'. The values on the FMC were 4.0/4.15 approximately.prior to starting the flight there was a NOTAM for military GPS jamming activity that could affect us up to approximately 400 nm of ZZZ. After departure approximately 5 minutes both GPS signals were lost and aircraft operated normally with no messages. We expected this. We continued on with no issues and followed procedure verifying our position and coast out check required with no GPS. After entering oceanic airspace as noted on chart and flight plan approximately 10 minutes later we received the 'unable reqd navigation perf rnp'. We ran checklist and began plotting our positions on the chart per procedures while we evaluated. Everything was fine and on course. We then began the process of advising dispatch and consulting with operations. We all concur and we continued normally with alternate plotting procedures. We then contacted ARTCC to advise of our degraded rnp above the rnp 4.0. They said fine and told us we had space for 100 nm. We asked them to pass along to the foreign ARTCC our condition and that was it.when we checked in with the foreign ARTCC (HF) we reported normally and tried to relay our degrade rnp to them. There was a language barrier and we knew they did not understand. So we messaged dispatch to have them call the foreign controllers and tell them via land line. They did and also noted to us that they thought the foreign controllers did not understand. A short while after that the foreign ARTCC called us on HF and asked us if we can comply rnp 10. We had a hard time understanding what he really meant but we eventually decided he was asking if we could comply with rnp 10 even though we were degraded from rnp 4.0. We replied and reported able to comply rnp 10. This was the end of all communication regarding our navigation issue. The rest of the flight proceeded normally via calls and plotting etc. And resulted in no navigational errors. We reported via VHF and received a code and were radar identified. Position based on radar fix was within 2 nm of what we showed. Flight continued without incident to our destination airport.

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Original NASA ASRS Text

Title: Air carrier flight crew reported they experienced a GPS signal loss during a NOTAMed military operation on an oceanic flight. The crew and their Dispatcher had language difficulty explaining the navigation capability loss to the foreign ARTCC.

Narrative: Enroute while in Oceanic airspace we got a message on the navigation display 'UNABLE REQD NAV PERF RNP'. The Values on the FMC were 4.0/4.15 approximately.Prior to starting the flight there was a NOTAM for military GPS jamming activity that could affect us up to approximately 400 nm of ZZZ. After departure approximately 5 minutes both GPS signals were lost and aircraft operated normally with no messages. We expected this. We continued on with no issues and followed procedure verifying our position and coast out check required with no GPS. After entering Oceanic airspace as noted on chart and flight plan approximately 10 minutes later we received the 'UNABLE REQD NAV PERF RNP'. We ran checklist and began plotting our positions on the chart per procedures while we evaluated. Everything was fine and on course. We then began the process of advising Dispatch and consulting with Operations. We all concur and we continued normally with alternate plotting procedures. We then contacted ARTCC to advise of our degraded RNP above the RNP 4.0. They said fine and told us we had space for 100 nm. We asked them to pass along to the foreign ARTCC our condition and that was it.When we checked in with the foreign ARTCC (HF) we reported normally and tried to relay our degrade RNP to them. There was a language barrier and we knew they did not understand. So we messaged dispatch to have them call the foreign controllers and tell them via land line. They did and also noted to us that they thought the foreign controllers did not understand. A short while after that the foreign ARTCC called us on HF and asked us if we can comply RNP 10. We had a hard time understanding what he really meant but we eventually decided he was asking if we could comply with RNP 10 even though we were degraded from RNP 4.0. We replied and reported able to comply RNP 10. This was the end of all communication regarding our navigation issue. The rest of the flight proceeded normally via calls and plotting etc. and resulted in no navigational errors. We reported via VHF and received a code and were radar identified. Position based on radar fix was within 2 nm of what we showed. Flight continued without incident to our destination airport.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.