Flight Crew reported the Flight Director commanded them to level off while conducting an RNAV approach due to failure to set the missed approach altitude. The crew continued the approach visually and became unstable resulting in a low altitude alert from the tower.
Synopsis
Flight Crew reported the Flight Director commanded them to level off while conducting an RNAV approach due to failure to set the missed approach altitude. The crew continued the approach visually and became unstable resulting in a low altitude alert from the tower.
Narrative
RJ in front of us slowed early and we had 40 kts. of overtake. We had to hurry and get fully configured and workload was high. After we passed ZZZZZ we forgot to put the MAP altitude in the altitude window due to the high workload. When we hit ZZZZZ1 the Flight Director (FD) directed a level off. We continued the approach visually and recognized we were getting low and leveled off. Due to the conflicting info from the FD; I switched to mental math to calculate the appropriate AGL for my descent while the Captain was trying to troubleshoot the FD so I could have accurate VNAV. At that point ZZZ Tower issued the low altitude alert and he told them correcting. I immediately leveled off as my VSI had increased a little more than the rule of thumb of GSx5 allowed. When we could see the PAPI we were slightly high and corrected and made an uneventful landing. Being more aware of the FAF and explicitly briefing it and directing the pilot monitoring (PM) to set the MAP altitude would have been key. Earlier configuration while keeping speed up would have allowed better workload management in terms of bleeding overtake. Continuing; in my opinion; was the right call as the workload at that moment to execute a go around would have caused confusion. Better configuration management. In that heavy airspace; configuring earlier than normal and keeping the thrust up to maintain speed is acceptable instead of trying to fly cleaner and faster longer. Better energy management. This is mainly an internal pilot flying thing for me to work on as someone who is still relatively new to the jet.
Second reporter narrative
We set up for the ZZZZZ.4 arrival and the RNAV (GPS) X Runway XX approach. The First Officer (FO) (flying pilot (FP) and myself (pilot monitoring (PM) briefed the arrival and approach. The ZZZZZ.4 arrival was uneventful and eventually we were cleared for the RNAV GPS X Runway XX approach. We planned to have the aircraft fully configured by ZZZZZ1 which we were doing. As we were approaching ZZZZZ getting configured ZZZ Tower informed us the regional jet (RJ) in front of us had slowed down and we had a 40 kt. overtake on the RJ. We quickly finished configuring and slowing the aircraft approaching ZZZZZ1. Because we were distracted by the RJ slowing so early and us having to quickly configure and slow our aircraft we forgot to set in the missed approach (MAP) altitude passing ZZZZZ and before arriving at the MAP altitude.At ZZZZZ2 the Flight Director (FD) commanded a level off which surprised us initially. The FO/FP asked what was happening and I told him that we forgot to set the MAP altitude. I told him to continue flying the lateral portion of the approach visually and I would give him rates of descent to fly. I told him to initially fly a 750 (ft. per minute) FPM rate of descent (ROD). He started a ROD greater than that causing us to get low in altitude as we were making the turn to line up with the extended runway centerline after ZZZZZ2. I could see this developing from my previous experience flying this approach and told him to level off which he finally did. Approximately in the area of the ZZZZZ3 waypoint ZZZ Tower issued us a low altitude alert and to check our altitude. I replied to them that we were 'correcting.' As we came around on the turn to final approach we were slightly high and I told the FO to start a ROD of about 750 FPM and fly the PAPI to the runway which he did to an uneventful touch down and landing. Not emphasizing in the briefing the high event fate/occurrences on this approach caused by crews forgetting to set the MAP altitude after passing ZZZZZ2. I read it but failed to prominently mention it to the FO/FP. Not monitoring the spacing with the aircraft in front of us by using the TCAS display. Even though this is not necessarily legal to do or use it would have been a useful tool for our situational awareness (SA). Instead of not going around (GA) relying on my previous lengthy experience flying this approach to talk the FO through it rather than going around. My experience would help in a situation like this but the proper thing to have done in this situation would have been to GA when ZZZ Tower gave us the low altitude alert. Not giving a very thorough briefing about the MAP and what events could trigger us to perform the MAP.Even though I had read the note on the company pages about the high rate of events; that described our event perfectly; neither of us mentioned nor emphasized that possible error. That should have been a high priority part of our briefing. In hind sight we should have performed a go around (GA) with the low altitude alert. I was concerned about the very high workload for a GA from that approach and from my previous 30 years of experience performing approaches into Runway XX I felt that it was safer to continue the approach while talking the FO through the final turn to final approach. A better approach would have been to very thoroughly brief the MAP and what events would trigger us to perform a MAP.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.