B777 first officer reported loss of GPS signal in the moscow area that lasted for about 20 minutes.

Narrative:

South of moscow and a few minutes south of amuti both GPS dropped offline. It took the jet a few minutes for us to see 'unable rnp' but our first indication was a solid yellow line under the pfd and then on the bottom of the nd the rnp was 2.00/2.67 'inertial' in yellow. It felt like solid 2-3 mins before we saw the 'unable rnp'. To that point we were discussing why we weren't seeing it. I was in the checklist looking for the 'unable rnp' when we received the EICAS msg. We enabled radio updating which almost immediately brought us back to .06 anp. But on the position reference page 3/3 the GPS info was blank so now the discussion became why we are not seeing 'GPS inop'. We never did see that. The GPS was blank for 5-10 mins before it came back online but when it did it was intermittent for a few mins; I took this as a normal boot up. While it was fixing itself the GPS would jump to 2.50 anp and .06 anp jumping between the two distances several times over 10-15 minutes. Radio updating had limited effectiveness due to the limited vors in the area. The inertial solution showed an anp of 19.6 the entire time; but wasn't a factor using/depending on it due to radio and GPS updates were more accurate. We also saw a jump from rnp 2 to 4. Now the GPS at 2.67 was compliant with the airspace so the script went from yellow to green. The whole incident lasted 20 mins and we never did witness GPS inop even though the data line for the GPS was blank for 5-10 mins.

Original NASA ASRS Text

Title: B777 First Officer reported loss of GPS signal in the Moscow area that lasted for about 20 minutes.

Narrative: South of Moscow and a few minutes south of AMUTI both GPS dropped offline. It took the jet a few minutes for us to see 'unable RNP' but our first indication was a solid yellow line under the PFD and then on the bottom of the ND the RNP was 2.00/2.67 'inertial' in yellow. It felt like solid 2-3 mins before we saw the 'unable RNP'. To that point we were discussing why we weren't seeing it. I was in the checklist looking for the 'unable RNP' when we received the EICAS msg. We enabled radio updating which almost immediately brought us back to .06 ANP. But on the position reference page 3/3 the GPS info was blank so now the discussion became why we are not seeing 'GPS Inop'. We never did see that. The GPS was blank for 5-10 mins before it came back online but when it did it was intermittent for a few mins; I took this as a normal boot up. While it was fixing itself the GPS would jump to 2.50 ANP and .06 ANP jumping between the two distances several times over 10-15 minutes. Radio updating had limited effectiveness due to the limited VORs in the area. The Inertial solution showed an ANP of 19.6 the entire time; but wasn't a factor using/depending on it due to Radio and GPS updates were more accurate. We also saw a jump from RNP 2 to 4. Now the GPS at 2.67 was compliant with the airspace so the script went from yellow to green. The whole incident lasted 20 mins and we never did witness GPS Inop even though the data line for the GPS was blank for 5-10 mins.

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.

Attributes
ACN	1446097
Time
Date	201703
Local Time Of Day	0601-1200
Place
Locale Reference	UUWV.ARTCC
State Reference	FO
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	B777 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Flight Plan	IFR
Component
Aircraft Component	GPS & Other Satellite Navigation
Person 1
Function	First Officer Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 180 Flight Crew Total 14000 Flight Crew Type 6000
Events
Anomaly	Aircraft Equipment Problem Less Severe Inflight Event / Encounter Other / Unknown