A321
Flight Crew Air Transport Pilot (ATP)
Confusion
Aircraft Equipment Problem Less Severe; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Aircraft
We received a full route reroute from clearance delivery. The First Officer (FO) entered and inserted the new route. We completed a full route check of the new route. After passing BAM Salt Lake Center asked us to confirm our route. At that point we realized that the points between BAM and DLL were no longer in the FMC. ATC said we could continue to DLL with no further comment. Neither the FO nor I are sure what happened to the route between BAM and DLL. We both feel it was properly inserted and checked; and there were no route modifications.
While on the ground in SFO; we received a full route clearance from ATC verbally. I entered the cleared route into the FMS; and then had the Captain check my work using the route clearance verification procedure as normal. All looked good and all points in the clearance were loaded. Enroute after passing BAM; ATC queried us on our cleared route of flight. It was at that point we saw that the FMS had dropped the routing between BAM and DLL; and was sending us direct. We told this to ATC; Salt Lake Center; who said it was no problem; and to continue direct to DLL.
Crew received a reroute during preflight; reprogrammed FMC; and crosschecked data. However; several waypoints dropped out causing a track deviation which was brought to the crew's attention by ATC.