Flight Crew reported an incorrect altitude read back and a CRM failure; resulted in a low altitude alert.
Synopsis
Flight Crew reported an incorrect altitude read back and a CRM failure; resulted in a low altitude alert.
Narrative
Flying as Aircraft X we were on the ZIGGY 7 arrival into SBD; SCT TRACON asked us with the winds they were landing SBD Runway 24 the winds were 280/11 we informed them that we would need Runway 6. SCT said we were number 2 due to and aircraft that was conducting the ILS 6 circle to land Runway 24 that we need to slow up and took us off the arrival and started vectoring us and assigning altitudes and started slowing us. SCT vectored us to a left downwind and descend to 4000 ft. SCT said turn left heading 140 descend to 3000 ft. PM (Pilot Monitoring) read back the instruction to SCT and pointed to 3000 ft. that I placed in altitude on the MCP. That heading would have put us inside SUDOC and I asked PM to extend me off of PETIS while descending SCT gave us a heading and cleared us for the approach. I selected approach and monitored our descent and our heading to join the localizer. SCT came back to us with an altitude alert to climb to 3400 ft. I turned off the autopilot and climbed back 3400 ft. SCT came back to us and said minimum vectoring in that area was 3400 ft. for terrain; we descended below 3400 ft. but I believe we were no lower than 3300 ft. The Controller said he gave us 3600 ft. but we read back 3000 ft. with no correction by SCT. Once we climbed to 3400; SCT recleared us for the approach and to maintain 3400 ft. till established on the glideslope. The flight continued with us flying the ILS 6 to a full stop landing with no further issues. The cause started back on the arrival when we were taken off ZIGGY 7 because you had a plan that you briefed now completely changed due to being vectored for the arrival and approach and situational awareness is not what you think you were going to get from being vectored. On the Ziggy 7 arrival I was expecting to fly south of the airport after overflying PETIS and then direct PDZ and vectors after PDZ to the ILS 6. On the segment from PETIS to PDZ I was expecting and altitude greater than 4700 due to minimum altitude for that segment. When SCT took us north of the airport for the left downwind for Runway 6 and descended us to 4000 ft. I didn't think to question the Controller about the altitude descent to 3000 ft. thinking it was coming in from a different direction and that 3000 ft. was the correct altitude to descend too. Also thinking I heard 3000 ft. and the PM read back of the Instruction to SCT without being corrected and PM pointing to the altitude I believed we were all on the same page. Next time I will be more alert of my situational awareness when things that you plan go totally different then planned and be more aware of altitude and heading being assigned by the Controller so that this problem would never happen again.
Second reporter narrative
The aircraft was turning base to final Runway 6 in SBD. SOCAL gave us a descend to 3600. The aircraft descended through 3600. As Pilot Monitoring I was looking outside for the Runway as it was VFR conditions. Then SOCAL told us to begin a climb to 3400 as there was a low altitude alert and that 3400 was the MVA in that area. The Pilot Flying turned off the Autopilot and began a climb by 3300 ft. and we preceded to immediately return to 3400 ft. During this there was a brief discussion on what altitude SOCAL had assigned. The altitude alerter had been set for 3000 and not 3600. The approach was continued and the aircraft landed without incident. The altitude alerter was set incorrectly on 3000 instead of 3600 and this caused the aircraft to descend below the 3600 ft.SBD with the high terrain and only one end of the Runway we are allowed to land on in our operations can prove difficult. That particular day we were close to our 10 kt. tailwind landing limitation. We were also taken off our original arrival and then given several vectors that compounded the complexity.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.