Date: 202011
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Final Approach; Initial Approach
ATC / advisory: TRACON ZZZ
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness; Time Pressure; Confusion; Distraction
Second reporter function: Pilot Not Flying; First Officer
Anomaly: Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Flight Crew Overcame Equipment Problem; Flight Crew Became Reoriented
Contributing factors: Aircraft; Human Factors; ATC Equipment / Nav Facility / Buildings
Primary problem: Ambiguous

Narrative: Vectored off of ZZZZZ 4 STAR and directed to descend to 5;000 feet and proceed direct to ZZZZZ and intercept the Runway XXL LOC. Loaded ZZZZZ in FMS; selected LNAV and armed LOC. While on a roughly southwest heading and proceeding direct to ZZZZZ in LNAV/VNAV; but still well east of Runway XXL we experienced a false LOC capture and the AFDS turned the aircraft to a heading of 176 degrees. Disconnected AFDS and de-armed the LOC and then used HDG Select to turn back to ZZZZZ. While in the process of turning back to ZZZZZ; Approach Control called us and said 'Flight AAAB I need you direct to ZZZZZ; turn right heading XXX.' We proceeded direct to ZZZZZ and landed uneventfully.PF and PM both recently returned to flying after long layoffs and that may have contributed. I knew for sure not to arm the Approach (APP) mode too early due to the aircraft either climbing to join the glide slope or descending on the glide slope before being established on the localizer; and was aware of the possibility of false localizer capture; but had never experienced a false LOC capture before.Using LNAV to intercept the LOC is a normal procedure; but possibly don't arm not only the APP mode; but also the LOC until within a few degrees of the ILS final approach course.  However this procedure could cause its own set of problems/conflicts by setting you up for flying through the LOC if you forget to arm the LOC.


Second narrative: We were assigned 5;000 feet; and given direct to ZZZZZ with instructions to join the localizer for [Runway] XXL there. Captain selected ZZZZZ and we proceeded direct in LNAV mode. He also armed LOC. About 8-10 miles northeast of ZZZZZ the aircraft falsely captured the localizer and began a turn south. Captain tried to select heading mode; but it initially would not select due to the false LOC capture. When we realized what happened; he deselected the LOC mode and began our turn back to ZZZZZ. About halfway through the turn back; ATC called and said he needed us direct ZZZZZ. We informed him we were in the turn; proceeded to ZZZZZ; and completed the approach without incident.The main cause was the premature capture of the localizer. I have not seen the aircraft do this before; and don't recall a warning or admonishment that it may. I don't plan on selecting LOC until closer to the intercept fix from now on; but I still don't believe this to be a crew error except that a slightly more timely response to the errant capture probably could have happened. The delay in response may have been quicker with a bit more recency of experience as both the Captain and I had recently returned from months long absences.Delaying LOC arming until closer to intercept is what I plan to do; though I don't think that is a perfect solution. I will study my manuals to try to determine why it happened; and a closer monitoring of the system should catch the fault earlier in the errant turn.


Synopsis: Air Carrier flight crew reported a false localizer capture; they were slow to react to the event and a track deviation occurred. The pilots stated an extended period of time off was a factor in their reaction time.