Air carrier flight crew reported receiving a low altitude alert from ATC while on a visual approach resulted in climb to minimum safe altitude.
Synopsis
Air carrier flight crew reported receiving a low altitude alert from ATC while on a visual approach resulted in climb to minimum safe altitude.
Narrative
Valley approach cleared us direct to SEBAS for Runway 17R. We were descending in VNAV PATH to 2000 ft. About 12 miles from SEBAS we were cleared for the visual approach to 17R and handed over to Tower frequency. The pilot flying (PF) dialed in 1300 ft. In the altitude window to help capture the glide slope and selected FLCH with the approach armed. A few miles From SEBAS while descending through about 1500 ft. Tower called us with a LOW ALTITUDE ALERT. The Captain disconnected the Autopilot and climbed back up several hundred feet. Then we intercepted the localizer and glide slope and landed uneventfully. We did not have any indications in the cockpit of low altitude; our only indication was from the Tower. Cause: The last few days we had been cleared direct to INFEQ for 17R. It is further from the runway and provides a longer straight in final to the runway. I think we got this alert from tower because of the intercept heading and altitude that close in to the runway. Suggestions: It could have been prevented by asking to go direct to INFEQ to set up for the visual approach further from the runway. It has worked great other times and we will request that in the future.
Second reporter narrative
When we were approximately 35 miles from the field; approach cleared us direct to SEBAS; which is on 4 mile final for 17R; with an FMS programmed altitude of 1320 ft. We were cleared to descend at our discretion to 2;000 ft. MSL; which I set in the altitude window and began a descent in VNAV PATH. When we were about 12 miles out from SEBAS; we were cleared for the visual and handed off to Tower. At this point; my belief was that staying in VNAV with a 45 degree intercept at SEBAS would result in the Autopilot and Flight Director System (AFDS) not capturing the glide slope at SEBAS; so I put 1300 ft. in the altitude window and selected FLCH. A few miles prior to SEBAS; we were descending through 1500 or 1600 ft.; and Tower called us and said the phrase 'low altitude alert.' At this point; we were around 1400 ft.; I disengaged the Autopilot and climbed approximately 200 ft.; then gradually descended back to 1300; intercepted the ILS; and landed uneventfully; having met stable approach criteria before 1000 ft. AGL. At no point did we get any cockpit indications of low altitude or any other anomalies (GPWS alerts; etc.)Cause: This event was caused by the large intercept angle for the visual; to a point relatively close in to the runway; and flying the approach with the idiosyncrasies of the AFDS in mind.Suggestions: In the past; we have been cleared to INFEQ; a point on about a 15 mile final; as a setup for the visual to 17R. This works out great every time; and in the future; when cleared to SEBAS; I will request INFEQ instead.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.