CL-350 flight crew reported descent toward terrain during approach. Flight crew climbed back to safe altitude and continued approach.
Synopsis
CL-350 flight crew reported descent toward terrain during approach. Flight crew climbed back to safe altitude and continued approach.
Narrative
On Day 0; I was SIC (Second In Command) on a Challenger 350 aircraft; operating from ZZZ to ZZZ1. At the time of our arrival; it was night time and the tower was closed. There were also 3 other airplanes in the traffic pattern. My partner did a great job coordinating with them and passing along their location to me. We elected to do a right downwind entry to runway XX; using the flight track to execute the downwind; base; and final legs of the visual maneuver. The field elevation at ZZZ1 is XX10' MSL. The touchdown zone elevation for runway XX is XX07' MSL. During my approach briefing; I stated that we would use 2000' for our stabilized approach criteria gate. Once we acquired visual contact with the airfield; I set 2000' in the AAD and initiated a descent using vertical speed; with the autopilot engaged. My intent was to intercept the 032° inbound course to ZZZZZ (the fix at the end of the downwind leg on the flight track) at pattern altitude. (1500' AGL). At about 2300'; LNAV mode engaged and the airplane turned to intercept the aforementioned inbound course. Shortly thereafter; the airplane began to capture 2000'. As this was happening; I had started to notice the ground was moving exceptionally fast underneath us; making me wonder if we were too low for our current position. As I started to scan between outside and inside the airplane; my partner started to state that we seemed to be getting low. Simultaneously; we received a master caution and a ground proximity message on our PFD's (Primary Flight Display). We also received a master warning due to the landing gear not yet being extended; since our thrust lever angle was low while being at or below 500' radio altitude. At this point; I hadn't fully realized my lapse in situational awareness; and started to wonder if my altimeter was faulty. (In my mind; I am at pattern altitude). As I disconnected the autopilot and began to add power and climb; we received an aural 500" from the radio altimeter. It was at this moment that I realized my mistake. When I briefed the stabilized approach gate altitude; that number stuck in my head. My first priority during the recovery was to achieve terrain clearance. After we recovered; the base turn was approaching and I was starting to get behind the airplane. My partner did an excellent job of providing me with callouts and suggestions to help us return to where we needed to be. After climbing and intercepting the appropriate lateral and vertical course for the approach; we both agreed that we were back in a safe position and elected to continue the approach. We conducted a normal landing.In hindsight; we were at the end of a very long tour and a very long day. My mental acuity was hindered by this; coupled with some expectation bias."
Second reporter narrative
ZZZ visual to runway XX utilizing the right hand traffic pattern. Altitude awareness was lost between the intercept to the downwind and turn to the two mile base leg. We were 200' low as we made the turn to base and the discomfort was noted in both of us but altitude was restored quickly without deviating from the lateral track. We opted to continue as we were back on the same page as to where the lateral and vertical commands were taking us. Base and final approaches were without incident. A debrief between the crew was helpful to determine both of our parts in the event. The high workload into a non towered airport at the end of a long day was no excuse. I let my guard down due to the exceptional past performance of my first officer. I focused on the traffic and calls to the airport and let him focus on the flying. I need to make sure I am effectively overseeing all aspects of the flights going forward.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.