Air carrier flight crew reported during initial approach receiving a low altitude alert from ATC. Flight crew immediately leveled off and climbed back to the correct altitude and continued the approach.
Synopsis
Air carrier flight crew reported during initial approach receiving a low altitude alert from ATC. Flight crew immediately leveled off and climbed back to the correct altitude and continued the approach.
Narrative
Flying into ZZZ; I was the pilot monitoring (PM). We were set up; briefed; and ATC told us to expect the ILS Z Runway XXL. Prior to commencing the approach; ATC changed our clearance to the RNAV VISUAL Runway XYR and started vectoring us to ZZZZZ. The pilot flying (PF) told me he was going 'heads down;' loaded the FMS for the approach; and subsequently briefed it. I was monitoring the aircraft during this time. Once the PF was back 'heads up;' I started reviewing the approach chart and taxi routes of what the PF had just briefed. We were direct to ZZZZZ; passing through 6;800 ft. (6;000 ft. assigned) using OP DES; when ATC cleared us for the approach. The PF set 2;800 ft. in the altitude selector and pressed APPR. I confirmed that 2;800 ft. was set and then turned my attention to the approach chart to verify that the altitude was appropriate. It took me a while to find the correct altitude on the approach chart as I had the RNAV (RNP) Z Runway XYR pulled up. By the time I realized that I was looking at the wrong chart; switched over to the correct one; and reviewed it; we received a low altitude alert from ATC. We were approximately 6 nm from ZZZZZ and had just descended below 5;200 ft. The mandatory altitude at ZZZZZ was 6;000 ft. The PF stopped the descent and climbed back up to 6;000 ft. Once established at 6;000 ft.; the rest of the approach and landing were uneventful.I had assumed that once the PF selected APPR; the aircraft would capture the vertical approach profile and level off at 6;000 ft. for ZZZZZ. The vertical mode column of the flight mode annunciator (FMA) showed OP DES as the active mode with ALT FINAL as armed. The lateral mode showed APP NAV as active. I should have been monitoring the altitude more closely until the aircraft leveled off at 6;000 ft. and the Flight Mode Annunciator (FMA) displayed FINAL APP. I also should have asked the PF why he set 2;800 ft. instead of confirming the altitude and then trying to figure it out with the approach chart. The field elevation at ZZZ is X;XXX ft. which means that the altitude set was less than X00 ft. AGL. As we have no procedure that directs us to set an altitude that low; it should have been my first indication that something was not set right. During the arrival briefing; I did not identify a possible runway change as a threat (based on experience and the direction that we were approaching the airport from). Had I identified that as a threat; we would have briefed the RNAV Visual Approach and would have been more familiar with the procedure; increasing our situational awareness.
Second reporter narrative
We descended into ZZZ via the ZZZZZ1 XXL transition. As we reached 8000 ft.; Approach instructed us of a runway change to XYR and the RNAV visual approach. The Captain and I rapidly loaded the approach and conducted a briefing. We were cleared to descend to 6000 ft. and direct ZZZZZ. Approximately 10 miles from ZZZZZ we were cleared for the approach. I selected approach mode and then set 2800 ft. as the bottom crossing restriction for the last fix on the approach. APP NAV was displayed on the Flight Mode Annunciator (FMA) and both the Captain and I confirmed the altitude. A moment later we received a low altitude alert from ATC and that ZZZZZ had a mandatory crossing alt of 6000 ft. I believe we were at 4900 ft. at this time. I immediately leveled off and then began a climb back to 6000 ft. to cross ZZZZZ at the correct altitude and continue the approach. From this point onward the approach and landing were uneventful.A VERY late approach change was the primary casual factor. Other aircraft ahead of us who requested to remain on XXL were either outright denied or told to expect extended delays. Additional factors would be the limited time to setup and brief the approach. Delay vectors could have been requested to help this; but the frequency was incredibly busy. This approach was conducted at the end of both a long duty and maximum block time day. I felt fully alert and fit for duty at the time; but if it had occurred earlier in the day I would have caught the mistake sooner.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.