A321
Flight Crew Air Transport Pilot (ATP)
Training / Qualification
ATC Issue All Types; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Other / Unknown
Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented
Aircraft; Environment - Non Weather Related
We were delayed leaving so we were in the very early morning hours when this happened. As we neared White Sands; NM our Dispatch advised us that the military was conducting GPS jamming exercises; so we were anticipating losing our GPS signals for a short time period. We got a warning on our FMGC that GPS signals were being lost. We were able to see on our FMGC that the signals had degraded. As we neared an intersection the aircraft began to bank the wrong direction in a 30 degree bank. I had to select heading to force the aircraft back on course. ATC then called and said we were 5 degrees off on heading to the next intersection. Once I had the aircraft back on course I found that we had lost both GPS signals completely. Apparently the FMGC weighs the GPS signal very highly and losing it from a very good to lost signal caused the aircraft to shift the perceived location enough to cause a 30 degree bank and ATC to see the error. Eventually we recovered GPS number 2 but GPS number 1 never came back online. After the signal was lost and things 'settled down' it seemed that the system was able to restore an accurate position. We confirmed position with basic VOR tuning and flying over the VOR. Military was conducting GPS jamming in area. Dispatch was aware that this was happening but ATC was not. We had a momentary loss of nav position as the FMGC had to adjust to the loss of its' best and most accurate signal. This adjustment meant we had a slight nav error. Please have ATC advised when GPS jamming will occur in their ATC zones. Please give pilots a method to disable GPS when jamming will occur to avoid the nav errors when the FMGC has to adjust to losing the GPS signal. Please give pilots a method for recovering a GPS signal when the receiver won't recover on its' own. Perhaps pilots will have to be advised to use heading when going into a GPS jamming area. ATC may need to increase separation if GPS jamming will occur as they are used to our aircraft having a very high level of nav accuracy.
A321 Captain describes the effects of military GPS jamming on his aircraft over White Sands late one night.