B777 flight crew reported they descended below the glide slope and received a low altitude alert from ATC. Flight crew became re-oriented and landed safely.
Synopsis
B777 flight crew reported they descended below the glide slope and received a low altitude alert from ATC. Flight crew became re-oriented and landed safely.
Narrative
During the ZZZZZ arrival and transition to ILS XXL we were direct ZZZZZ1. I was flying and using the RNAV approach technique; and once we were cleared the ILS XXL I armed the approach and had LNAV/VNAV active with LOC and GS armed. We initially set 1500 feet on the MCP (Mode Control Panel) for the ZZZZZ2 final approach fix crossing altitude. Weather was excellent: dark; but clear with good visibility. Before reaching ZZZZZ3 I visually acquired the runway XXL and disconnected the autopilot. Once we were on the leg to ZZZZZ3; we set the touchdown zone elevation. I was mostly flying visually and cross referencing my EFIS (Electronic Flight Instrument System) display. I captured the localizer and fully configured outside the ZZZZZ2 fix. I was still visual and following the flight director guidance when I realized I was low. I ignored the FD (Flight Director) and leveled off about 1300 feet; verifying low was all red PAPI; and GS showing low too. About this time I think ATC inquired and asked if we had runway and terrain visually and we replied yes. Soon afterwards the glide slope captured and I made a normal landing. With the benefit of hindsight; I was at the end of a true all night flight and failed to transition away from RNAV procedures to ILS on the intercept leg from ZZZZZ3. I should've left the 1500 feet in the MCP; leveled off at that altitude until glideslope captured. I also didn't notice the glideslope ghost" pointers on my ADI also telling me that I was below GS."
Second reporter narrative
On approach into ZZZZ I was Pilot Monitoring. We were flying the ILS approach to runway XXL from the ZZZZZ arrival. The Captain was flying the approach and elected to remain in LNAV/VNAV. When cleared for the approach he asked for touchdown zone elevation in the altitude window. Glideslope intercept should have occurred at 1500'; but it did not capture. VNAV gave direction to continue descending below 1500 feet. We all missed this error initially; but at about 1100-1200 feet; the Captain; Relief Pilot and I all realized we were low on the approach. The Captain immediately leveled off and captured the glideslope. We were advised by ZZZZ approach to maintain 1500 feet until on the glideslope after we identified our error. Landing was normal. After landing; tower asked us if we were in visual conditions for the approach. I said that we were. ATC Issued Low Altitude Warning. Altitude Deviation.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.