Commercial Fixed Wing
Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument
Flight Crew Last 90 Days 125; Flight Crew Total 2500; Flight Crew Type 800
Distraction; Human-Machine Interface
Inflight Event / Encounter CFTT / CFIT
Flight Crew Overrode Automation
Airport; Airspace Structure; Chart Or Publication; Environment - Non Weather Related
While on visual approach to COS [Runway] 35L; crew both identified a very large building under construction with crane offset between 1.7 to 2 miles from the runway threshold. At approximately 1.5 miles from threshold; received EGPWS (Electronic Ground Proximity Warning) 'Obstacle; Pull Up!' warning. Aircraft was stable and on visual glide path as verified by FMS 3 degree visual glide path indicator and also visually with Runway 35L PAPI. Sink rate at time of incident was 500 ft. per minute. As the building was either directly underneath or just behind aircraft; no other obstacles were noted and aircraft was stable and on glide path; PIC (Pilot-in-Command) decided this was an erroneous warning and elected to continue flight. Landing was uneventful. During debrief; both crew members agreed that the message was erroneous and must be an anomaly caused by the new construction and a go-around at that time would be futile. If the weather was not CAVU (Ceiling and Visibility Unlimited) an immediate go-around would have been performed. There is a current NOTAM (01/037) regarding a crane at this location but the crane was offset from the flight path and at 300 ft. AGL. An issue exists with the EGPWS system and this new building construction that will trigger false warnings and may cause aircraft to go-around unnecessarily.
Air carrier First Officer reported receiving a Ground Proximity alert even though they were on glidepath and flying a stabilized approach to COS airport. The reporter believes the alert was due to construction of a new building underneath the final approach course.