Air carrier flight crew reported during visual approach they descended below glide path resulting in a CFTT event. When flight crew recognized four red PAPI lights; they corrected altitude and continued approach.
Synopsis
Air carrier flight crew reported during visual approach they descended below glide path resulting in a CFTT event. When flight crew recognized four red PAPI lights; they corrected altitude and continued approach.
Narrative
ATC cleared us to descend via arrival then at EDDYY transition to the Tipp Toe visual 28L. We set 6000 ft. Approaching EDDYY; ATC told us to descend to 4000ft. PF (FO) select LVL CHG. ATC advised us traffic Aircraft Y going to 28R. While looking for the traffic; ATC asked us to slow down to 210 kts and if we have the airport and bridge in sight and the traffic. Finally saw the traffic and told ATC airport; bridge and traffic in sight. ATC told us to maintain separation and cleared us for the visual. So we dialed in 1800 ft on the altitude window. We were focusing to make sure we don't overshoot the path because of the traffic threat. Then ATC told us to slow down to 180 then 160 kts until the bridge. PF (FO) asked for gear and flaps configuration to slow down. Confirmed no overshoot. PM (Captain) realized we were inside the approach and asked to set TDZ while heads down to do the configuration changes asked by PF. ATC told us to switch to Tower. Both did not realize we were still in LVL CHG. (Tasked saturated) Accomplished landing checklist before 1000 ft. Approximately 4NM from the runway. I saw 4 red dots then realized we were low. It was around 750 ft. I told the FO (PF) to disconnect autopilot and arrest the descent and hand fly [to] get back on path. Realized we never re-engaged VNAV. Tower on their side told us to check altitude. Corrected the issue. Re-established the glide path. Stable and cleared to land. Landed normally. Exited runway and taxied to the gate. Debriefed it. Identified [that] traffic was the primary reason for distraction and ATC due to multiple instructions at the same time.
Second reporter narrative
Descending via SERFR 4 EDDY into SFO; with expect visual 28L (backed up with ILS). Initially descending to 6k at Eddy. Advised of Aircraft Y merging traffic same altitude for Runway 28R. On arrival given descend 4k and slow to 210 kts. Speed window opened. Used Level Change to descend. Just outside final approach course; given cleared for tiptoe visual 28L. Still searching for traffic. Set 1800' (final). Given slow to 180. Traffic in sight. Same altitude. Started configuring. Flaps 2; flaps 5. Turned final. Given 160 kts. Gear down; flaps 15. Confirmed no overshoot. Paralleling traffic. Told to maintain 160 until bridge; contact Tower. Set touchdown zone (still in Level Change). Flaps 25; flaps. 30; landing checklist. Right at bridge adjusted for target speed. Approx. 3-5 nm final; both pilots noticed we were low. CA said hand fly and climb. Disengaged autopilot increased pitch and disengaged Authrottle. Saw 4 red and approx 700' agl as lowest altitude. Set missed approach altitude. Armed approach for ILS backup. As we were arresting descent and getting back to path ATC called us to check altitude and not descend any further. Re-established on the glide path. Stable; and cleared to land. Landed normally. Exited Runway at Echo; over to Ground; and taxied to Gate. Parked; shutdown aircraft; and debriefed. Recognized we never re-engaged VNAV; or armed approach (for ILS) when cleared. Both would have corrected issue. Identifying Traffic on parallel was primary reason for distraction. Additionally; the various speed restrictions; and complacency of being on the visual aided to the unplanned automation configuration.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.