ZOA controller noted an enroute aircraft approximately ten miles off course potentially leading to a...

Narrative:

Air carrier X checked on FL340 destination smf. Flight plan read as expected MVA.swr.Flunk3.smf. Four minutes later; I observed the aircraft 10 miles south of MVA VOR. I inquired at got an unreadable response for which I replied with maintain present acknowledge with 'identify.' pilot then clearly read back the present heading clearance. I then asked if pilot was aware they were approximately 10 mile off course to the south and if they were having any GPS issues. After a slight delay the pilot replied 'yes we are.' GPS jamming was taking place by [the military]. If the pilot would have noticed they were off course before I did and corrected the course it would have caused aircraft to turn right approximately 30-40 degrees into opposite direction eastbound FL325 climbing to FL350. Aircraft were laterally separated by approximately 7 miles. Not sure as to why GPS jamming was taking place but maybe it should only take place during mid shift operations.

Original NASA ASRS Text

Title: ZOA Controller noted an enroute aircraft approximately ten miles off course potentially leading to a loss of separation. After questioning the pilot; Military GPS interference was identified as the causal factor.

Narrative: Air Carrier X checked on FL340 destination SMF. Flight plan read as expected MVA.SWR.Flunk3.SMF. Four minutes later; I observed the aircraft 10 miles South of MVA VOR. I inquired at got an unreadable response for which I replied with maintain present acknowledge with 'IDENT.' Pilot then clearly read back the present heading clearance. I then asked if pilot was aware they were approximately 10 mile off course to the South and if they were having any GPS issues. After a slight delay the pilot replied 'yes we are.' GPS jamming was taking place by [the Military]. If the pilot would have noticed they were off course before I did and corrected the course it would have caused aircraft to turn right approximately 30-40 degrees into opposite direction Eastbound FL325 climbing to FL350. Aircraft were laterally separated by approximately 7 miles. Not sure as to why GPS jamming was taking place but maybe it should only take place during mid shift operations.

Data retrieved from NASA's ASRS site as of July 2013 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	1055724
Time
Date	201212
Local Time Of Day	1801-2400
Place
Locale Reference	ZOA.ARTCC
State Reference	CA
Aircraft 1
Make Model Name	MD-80 Series (DC-9-80) Undifferentiated or Other Model
Flight Phase	Cruise
Flight Plan	IFR
Person 1
Function	Enroute
Qualification	Air Traffic Control Fully Certified
Events
Anomaly	ATC Issue All Types Deviation - Procedural Clearance Deviation - Track / Heading All Types

ZOA controller noted an enroute aircraft approximately ten miles off course potentially leading to a loss of separation. After questioning the pilot; military GPS interference was identified as the causal factor.