Date: 202201
Local time of day: 1801-2400
Location: COS.Tower, CO
Flight conditions: VMC
Light: Night
Aircraft: Large Transport; Low Wing; 2 Turbojet Eng
Operator: Air Carrier
Operating under: Part 121
Flight phase: Initial Approach
ATC / advisory: Tower COS
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Human factors: Situational Awareness; Confusion; Communication Breakdown
Second reporter function: Pilot Flying; First Officer
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Detector: Automation Air Traffic Control; Person Flight Crew; Person Air Traffic Control
When detected: In-flight
Result: Flight Crew Became Reoriented
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: On downwind on the east side of COS flying northbound; the FO/PF (First Officer/Pilot Flying) said he had the field in sight and we were cleared [for] the visual approach to [Runway] 17R. The PF mentioned planning to roll out on about a 3-4 mile final and I cleared the FMS up to AGHU on the RNAV approach as he requested. The PF began to configure early so I inquired about it and he said he still wanted to configure; so I did; as he called for flaps and gear. As he turned the base leg I told him he was way too low out here; that the terrain rises to the north; and that the white bar on the altimeter is indicating 1000 ft. above field elevation but the field was 4-5 miles southwest of our position and that our Radio Altimeter was between 600-700 feet AGL. At that point; COS tower asked about our situation and mentioned that he had received a low altitude alert from his equipment in the tower. I replied that we were ok. As the PF turned his base to final early; I told him 'that's the wrong runway; the runway is that way' and I pointed to where he needed to aim the jet. The PF mentioned something to the fact that he had been looking at the incorrect runway (17L) and I believe this is the main reason he had configured and descended so early. I believe the main cause was a combination of the PF not being very familiar with the airfield and local area and accepting a visual approach at night without continuously backing up what he was seeing outside vs the instruments inside the cockpit that had the instrument approach loaded to the correct runway. I could have asked more/better questions about what he was seeing or why he was wanting to configure so early. That might have uncovered some clues to me that the PF was looking at the incorrect runway and not cross checking with his instruments.


Second narrative: On downwind to Runway 17R at COS we were cleared for the visual approach. Turning base; Tower told us they were receiving a low altitude alert and asked if we could maintain our own terrain clearance. We said we could and continued to an uneventful landing on Runway 17R. Should have stayed higher until the base turn. Unfamiliar landing south at COS.


Synopsis: Air carrier flight crew reported receiving a low altitude alert during approach to land.