Air carrier captain reported intermittent GPS signal loss in an area of notamed GPS jamming activity...

Attributes
ACN	1539318
Time
Date	201805
Local Time Of Day	0601-1200
Place
Locale Reference	GJT.Airport
State Reference	CO
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	Medium Large Transport Low Wing 2 Turbojet Eng
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Flight Plan	IFR
Component
Aircraft Component	GPS & Other Satellite Navigation
Person 1
Function	Captain
Qualification	Flight Crew Air Transport Pilot (ATP) Flight Crew Multiengine Flight Crew Instrument
Experience	Flight Crew Type 580
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Track / Heading All Types

Narrative:

In cruise; after taking back pilot flying duties (had been dealing with passenger illness situation) noticed a 'GPS primary lost' message. While referencing the flight manual and fom; the message cleared and the GPS and navigation systems appeared to function normally. There was an enroute NOTAM about GPS possibly being unusable; but at this point; it was operations normal. Took this opportunity to switch to plan mode and check STAR constraints. While doing this; ATC queried us as to where we were going. At this point noticed a 'navigation degraded' message. Informed ATC we were having GPS issues. They gave us a heading and mentioned there was GPS jamming tests going on yesterday. GPS did go out a couple of times after that; but very briefly and close to the notamed area. Rest of flight operations normal; though we did notify ATC through another sector and notified dispatch.

Original NASA ASRS Text

Title: Air carrier Captain reported intermittent GPS signal loss in an area of NOTAMed GPS jamming activity.

Narrative: In cruise; after taking back Pilot Flying duties (had been dealing with passenger illness situation) noticed a 'GPS Primary lost' message. While referencing the Flight Manual and FOM; the message cleared and the GPS and navigation systems appeared to function normally. There was an enroute NOTAM about GPS possibly being unusable; but at this point; it was operations normal. Took this opportunity to switch to Plan Mode and check STAR constraints. While doing this; ATC queried us as to where we were going. At this point noticed a 'NAV Degraded' message. Informed ATC we were having GPS issues. They gave us a heading and mentioned there was GPS jamming tests going on yesterday. GPS did go out a couple of times after that; but very briefly and close to the NOTAMed area. Rest of flight operations normal; though we did notify ATC through another sector and notified dispatch.

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.