2024-06 · NASA ASRS report 2137481
Air carrier flight crew reported receiving a low altitude alert from ATC on approach to DCA.
When cleared for the RNP approach Runway 19 into DCA we missed an altitude restriction at DERIC and GREYZ. When cleared for the approach we proceeded direct to FERGI and forgot to rearm VNAV after being vectored through the final approach course. During the descent we had been in and out of VNAV due to weather and aircraft spacing. Upon being vectored away from FERGI we placed the aircraft into a Level Change descent to comply with ATC instructions. Once we were cleared for the approach the aircraft was not placed back into VNAV. I believe a major factor contributing to this event was unrealized fatigue. During the approach I remember going through the checklist in my head; but I don't remember selecting any buttons on the Mode Control Panel (MCP) or checking the Flight Mode Annunciator's (FMAs) after doing so. It was at this point I realized that I was more tired than I had noticed during the flight. I believe the aircraft was on the path crossing FERGI which was why I did not notice the aircraft being off path until DERIC. When I began configuring the aircraft for landing the increased drag caused us to descend faster; which I did not notice because I became fixated crosschecking the lateral position of the aircraft on the approach. About the time we crossed DERIC I felt that the vertical position of the aircraft was low.At this time I checked both the FMC and the approach plate for the correct altitude and realized we had missed the restriction at DERIC and were about to continue below the restriction between DERIC and GREYZ. At this time I disconnected the autopilot and leveled the aircraft at aroudn 1650 ft. MSL and climbed back up to 1700 ft. MSL as that was the restriction on the portion of the approach we were on. At this time ATC also noticed our deviation with a low altitude alert and was acknowledged by the First Officer. We attempted to place the aircraft back into VNAV and turned on the autopilot however the aircraft started to begin a decent again. I disconnected the autopilot again; maintained 1700 ft. and elected to continue the approach as the aircraft was stable and now established on the correct vertical and lateral portions of the approach and we were in visual conditions. We continued the approach with the autopilot off and manually verified the vertical altitudes throughout the rest of the approach and landed without further issue.For the fatigue portion. The first overnight was in ABQ and we arrived slightly late and then it takes me about an hour to wind down and get to sleep. In order to get a full 8 hours of sleep at the hotel I had to force myself to sleep for the last hour or two because I am acclimated to the East Coast. The second overnight in Nashville it took us over an hour to get to the hotel due to a concert letting out and then after I wound down and tried to go to sleep there was still a large amount of partying going on outside of the hotel that I could hear in my room even on the 20th floor. We got to the hotel about midnight. I was woken multiple times during the first part of the night; but I do not know how late into the night the noise went. I attempted to have white noise on my phone to drown the noise as well but it was not enough. In the morning I woke up around 9am and felt rested. Then during our first deadhead I felt myself get tire and was able to take about a 45 minute nap. This was probably why I felt rested for the majority of the flight to DCA. However my fatigue level was quite apparent after landing and during the drive home.
Got vectored around and through FAC; also given a descent clearance from 5000 to 3000. Then given instructions to cross FERGI at 3000 ft. and clears for the RNP 19. The CA was the PF and didn't engage VNAV; he was still in LVL Change. I dialed in the TDZ elevation once we crossed FERGI. He noticed we were low; disconnected autopilot (AP) and climbed back up to alt. We then got a call from Tower about a low altitude alert. I acknowledged and we confined the rest of the approach without incident to a full landing.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.
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