Date: 201509
Local time of day: 1801-2400
Location: PCT.TRACON, VA
Flight conditions: Mixed
Weather elements / visibility: 10
Light: Night
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class E PCT
ATC / advisory: TRACON PCT
Reporter organization: Air Carrier
Reporter function: Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Second reporter function: First Officer
Anomaly: Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Air Traffic Control Provided Assistance; Flight Crew Overcame Equipment Problem; Flight Crew FLC Overrode Automation; Flight Crew Became Reoriented; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Chart Or Publication; Procedure; Company Policy
Primary problem: Chart Or Publication

Narrative: We were on the [STAR 1] Arrival on the Left transition heading to [waypoint ZZZ1] when ATC asked if we were descending via [STAR] Arrival. We replied that were indeed descending via the [STAR]. The Approach Controller said it appeared we were not doing so as the aircraft was observed heading on a southeast course. After back and forth communication between us and the Controller verifying the route; we were vectored off the arrival and issued radar vectors.The Approach Controller was as perplexed as to our location and was trying to help us determine the issue asking if the arrival in the FMS was indeed entered as the [STAR] to which we replied that the FMS is displaying [STAR]. The Approach Controller did inform us that there will be an [STAR 2] being issued soon that DOES move [waypoint ZZZ1] to the southeast.After further review; we noticed the FMS DATABASE had been inadvertently selected to the next data cycle (date).  We tried to move it back to the (date) database but could not until the aircraft was on the ground.What really made us confused was that the [STAR] had changed in the new data cycle; but was still labeled [STAR 1] and not [STAR 2] which would have given us more of a warning that something was not right. We definitely would have caught the error on the ground in [airport] during the route programming check.Even though the [STAR 1] Arrival was going to change; the numerical identifier may not always change; so don't assume everything is correct just because the title didn't change. This may be an early heads-up that the revised [STAR 2] and the old [STAR 1] are different and should be revised as the [STAR 2] if that change is not already in the works. A substantial waypoint position change on a procedure should require a renaming of the waypoint.


Second narrative: We were on the [STAR 1] Arrival for on the Left transition heading to [waypoint ZZZ1] when ATC asked if we were descending via [STAR 1] Arrival. We replied that were indeed descending via the [STAR 1]. The Approach Controller said it appeared we were not doing so as the aircraft was observed heading on a southeast course. After back and forth communication between us and the Controller verifying the route; we were vectored off the arrival and issued radar vectors.The Approach Controller was as perplexed as to our location and was trying to help us determine the issue asking if the arrival in the FMS was indeed entered as the [STAR 1] to which we replied that the FMS is displaying [STAR 1]. The Approach Controller did inform us that there will be an [STAR 2] being issued soon that DOES move [waypoint ZZZ1] to the southeast.After further review; we noticed the FMS DATABASE had been inadvertently selected to the next data cycle (date). We tried to move it back to the (date) database but could not until the aircraft was on the ground.What really made us confused was that the [STAR 1] had changed in the new data cycle; but was still labeled [STAR 1] and not [STAR 2] which would have given us more of a warning that something was not right. We definitely would have caught the error on the ground in [airport] during the route programming check.Even though the [STAR 1] Arrival was going to change; the numerical identifier may not always change; so don't assume everything is correct just because the title didn't change. This may be an early heads-up that the revised [STAR 2] and the old [STAR 1] are different and should be revised as the [STAR 2] if that change is not already in the works. A substantial waypoint position change on a procedure should require a renaming of the waypoint.


Synopsis: An aircraft deviated off the assigned STAR. Crew had inadvertently set the FMS to program from the next charting cycle date instead of current charting cycle. The aircraft was proceeding along the route of a revision to the STAR which was not yet in effect.