A320 flight crew experiences GPS jamming in ZLC airspace resulting in a momentary track deviation. T...

Attributes
ACN	1261551
Time
Date	201505
Local Time Of Day	0601-1200
Place
Locale Reference	ZLC.ARTCC
State Reference	UT
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	A320
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Flight Plan	IFR
Component
Aircraft Component	GPS & Other Satellite Navigation
Person 1
Function	Pilot Not Flying Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 70 Flight Crew Total 15000 Flight Crew Type 7000
Person 2
Function	Pilot Flying First Officer
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 240 Flight Crew Total 10000 Flight Crew Type 8430
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Procedural Clearance Deviation - Track / Heading All Types

Narrative:

With autopilot 2 engaged; the aircraft initiated a turn to the left to correct back to what it perceived as its FMGC generated course. The turn was fairly aggressive; 30 - 40 degree intercept; and was questioned by the pilots. A message then appeared on mcdu screen FMGC 1/2 disagree. We noted that; although both boxes indicated that they were both in high accuracy with estimated position deviations of only 0.08 mile; they did; in fact; disagree by almost four miles. We did not know which; if either was correct and were about to query ATC when they contacted us; asking why we were deviating to the north. Aircraft was already correcting to course when we received the call. Turns out; FMGC 2's course was possibly corrupt and that was what the aircraft was following. Within approximately one minute; the two FMGC's updated each other; generating a single accurate course. We informed ATC of the transient downgrade. In addition; GPS was being jammed across the utah area; with GPS lost message on CRT; but had recovered to GPS primary at time of event.

Original NASA ASRS Text

Title: A320 flight crew experiences GPS jamming in ZLC airspace resulting in a momentary track deviation. The jamming was NOTAMed but the aircraft's reaction to the jamming was unexpected.

Narrative: With autopilot 2 engaged; the aircraft initiated a turn to the left to correct back to what it perceived as its FMGC generated course. The turn was fairly aggressive; 30 - 40 degree intercept; and was questioned by the pilots. A message then appeared on MCDU screen FMGC 1/2 disagree. We noted that; although both boxes indicated that they were both in high accuracy with estimated position deviations of only 0.08 mile; they did; in fact; disagree by almost four miles. We did not know which; if either was correct and were about to query ATC when they contacted us; asking why we were deviating to the north. Aircraft was already correcting to course when we received the call. Turns out; FMGC 2's course was possibly corrupt and that was what the aircraft was following. Within approximately one minute; the two FMGC's updated each other; generating a single accurate course. We informed ATC of the transient downgrade. In addition; GPS was being jammed across the Utah area; with GPS lost message on CRT; but had recovered to GPS primary at time of event.

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.

A320 flight crew experiences GPS jamming in ZLC airspace resulting in a momentary track deviation. The jamming was notamed but the aircraft's reaction to the jamming was unexpected.