Air carrier crew reported receiving a low altitude alert from ATC during an unstabilized approach with a high descent rate. The crew re-captured the glide path; re-stabilized the aircraft; and continued the approach.
Synopsis
Air carrier crew reported receiving a low altitude alert from ATC during an unstabilized approach with a high descent rate. The crew re-captured the glide path; re-stabilized the aircraft; and continued the approach.
Narrative
Arriving into HKG on the ABBEY 2B arrival for landing on runway 25R. I was the PF and FO was the PM. I started the approach briefing well prior to the top of descent; but continued briefing in the descent due to the complexity of the RNAV TRANSITION to ILS Rwy 25R and the ILS Rwy 25R plates coupled with an early descent given by the HKG controller prior to the FMC calculated top of descent.During my briefing the HKG controller then vectored us off the ABBEY 2B Arrival in the direction of RUNSU (310 deg heading) which was the first point on the extended final for Rwy 25R. The briefing coupled with the shortened vectors led to a time/altitude compression situation which was challenging. Further complicating the arrival was the numerous radio calls by approach for speed reductions and descents. We missed the initial radio call from HKG Approach for clearance for the RNAV TRANSITION to ILS Rwy 25R. Because of this we did not have the FAP (Final Approach Point) altitude of 1700 feet set in a timely manner in our MCP (Mode Control Panel) altitude window.Once the confusion was resolved regarding approach clearance we were past RUNSU in VNAV ALT high on the approach transition profile. In order to meet the subsequent mandatory altitude of 3800 feet on the RNAV transition I chose to disconnect the autopilot and hand fly the aircraft since we were in Day VMC conditions with the terrain in sight. I also asked the PM to push the altitude knob to transition to a descent. This resulted in an excessive descent rate which apparently triggered the HKG approach contoller's altitude warning system. My recollection was that I crossed SAGNI high at approximately 4000 feet (3800 ft mandatory on the plate).Due to task saturation on the approach; I don't recall exactly where the controller made the alert call; or where we intercepted the ILS glidepath after TOPUN (earliest point for selecting Approach mode); but we were fully configured; on profile; and stable at target speed at 500 feet.We did not have any EGPWS (Enhanced Ground Proximity Warning System) or GPWS alerts from our airplane at any point on the RNAV Transition or ILS Approach to Rwy 25R.
Second reporter narrative
I was Relief Pilot sitting behind the FO who was PM into HKG. We were flying the ils 25R transition to the ILS 25R in visual conditions with SCT clouds. We were cleared direct TEDAP initially and then cleared direct RUNSU. We were given; multiple speed changes and cleared to descend 4500ft. We were given a late approach clearance which left us high crossing VH515 approaching SAGNI which has a mandatory restriction of 3800ft. When the captain realized he was going to be high he turned off the AP (Autopilot) and started a rapid descent to meet the restriction. From my perspective and position in the cockpit it looked like we were close on the restriction but I am unsure as to how high we were off. At some point the captain asked the MCP (Mode Control Panel) to be set for the FAF at 1700ft it is at that point I believe the ALT button was pushed and the 2700ft restriction was deleted at TOPUN. I believe the aircraft calculated a different descent path which may have contributed to the low altitude alert. The captain was still hand flying at this point and had the boards out. I saw the glide slope trending upwards and he was slightly below the magenta VNAV path. It appeared he was looking at the MCP. I was concerned we were going to be further below path so I called check path". That brought everyone back to their PFD (Primary Flight Display) and shortly after we got a call from approach that they had a low altitude alert from us. In visual conditions it did not appear we were that low based on the GS we were about a dot below but approaching VH536 at 1800ft still and still on the magenta vnav path. We intercepted the GS from there and continued the approach uneventfully. I either believe we had too high of a descent rate which triggered the low altitude alert or we deleted the restriction which created a path lower than expected. I believe some of the factors that contributed to the mistakes made on the approach were getting behind the aircraft which was both ATC induced and self induced with a late and lengthy approach briefing from the captain."
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.