B737 Next Generation Undifferentiated
Flight Crew Air Transport Pilot (ATP)
Confusion; Distraction; Human-Machine Interface; Situational Awareness
ATC Issue All Types; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Requested ATC Assistance / Clarification; Flight Crew Returned To Clearance; Flight Crew Took Evasive Action
ATC Equipment / Nav Facility / Buildings; Airport
On approach to Runway 16R in Seattle in scattered cloud conditions while visually following preceding traffic to the runway I armed the ILS approach mode as a backup to the briefed visual approach. All ILS approach and arrival briefings were accomplished. ATIS was advertising approaches to 16L and 16R and departing 16L. We were told to maintain 3;200 until BUGNE then cleared 16R. I noticed the aircraft cross slightly to the left of the 16R centerline so I disconnected the autopilot and corrected back to the 16R centerline. The identifier for the ILS showed 34L so we continued the visual approach to uneventful landing. After blocking in at gate we called ground control to inform them that the 34L localizer was active. I called Tower and TRACON on the telephone to inform them of the issue also. The TRACON Supervisor told me the localizer was supposed to be down for maintenance and that the 34L localizer should not have been operating.There were two primary issues. First; the localizer was active for the opposite direction runway when it should have been off. Second; I armed the approach as a backup while not visually assuring the identification. The deviation was identified and only a minor deviation occurred.
A B737 pilot flying a SEA Runway 16R visual approach in the ILS APP Mode noted a track deviation and while manually flying back to centerline noticed the Runway 34L ILS identifier was active. ATC reported the 34L ILS was supposed to be off line.