B737 flight crew reported receiving a ground proximity terrain warning during approach while descending below the minimum altitude. After hearing the ground proximity aural warning; the flight crew conducted a go-around to a safe landing.
Synopsis
B737 flight crew reported receiving a ground proximity terrain warning during approach while descending below the minimum altitude. After hearing the ground proximity aural warning; the flight crew conducted a go-around to a safe landing.
Narrative
Approaching ZZZZ the FO (First Officer) and I briefed the ZZZZZ STAR with the ZZZZZ transition to ILS Runway XX. During the brief we confirmed the STAR and ILS Runway XX approach were joined via the ZZZZZ transition. Once transferred to the Approach Controller we were cleared direct to ZZZZZ and cleared for the ILS Runway XX approach. Because we were cleared for the approach; the STAR and ILS approach were joined via the ZZZZZ transition; and the vertical mode was VNAV PATH; I called for and the FO set the FAF altitude of 7700 ft. The course change between the approach to ZZZZZ and the final approach course was nearly 90 degrees. During the descent I opened and closed the SPEED window for speed control. I made a mental note that the aircraft seemed to be lower by about 100 ft. than the mandatory 9000 ft. at ZZZZZ as it made the turn to join the final approach course. I attributed this to the fact that ZZZZZ was a fly-by point and figured I was simply miscalculating where the abeam point was. As we were now on a published portion of the approach with VNAV still selected I called for touchdown elevation to be set in the MCP (Mode Control Panel) and armed the approach at the same time. VOR/LOC and glideslope were armed and VOR/LOC captured. Shortly afterward the FO made a comment about our altitude and the restriction at ZZZZZ1. Shortly after I faintly heard caution; terrain" from the aural warning unit. I immediately disconnected the autopilot and autothrottle and added full power and pitched up to approximately 20 degrees nose up. What followed was "clunky" go-around procedure as I was suffering a little from the startle effect. The aircraft was returned to a clean configuration and a go-around was called by the FO to ATC. ATC instructed us to climb to 11000 ft. and issued a turn. ATC issued vectors for an additional approach and a subsequent ILS Runway XX was successful. We landed; taxied in; and parked with no further issue."
Second reporter narrative
After two aircraft swaps with a return to gate and almost 3 hours late; we proceeded to ZZZZ with no further issues until we started the approach. With thunderstorms in the area and around the airport we got direct to ZZZZZ which is one of the initial approach fixes on the ILS Runway XX. Prior to crossing ZZZZZ we were instructed to cross ZZZZZ at 9000 ft. and cleared for the ILS Runway XX. As we crossed ZZZZZ the Captain pressed Approach Mode on MCP (Mode Control Panel) and asked to set touchdown zone elevation; which I did. I believed since we had VNAV engaged the aircraft would respect the altitudes on the approach until interception of the glideslope. As the aircraft intercepted VOR/LOC between ZZZZZ and ZZZZZ1 I looked outside and even when it was dark; I could see terrain getting closer. The Captain I believe had terrain mode and I had radar mode on my screen. I checked the approach chart and our altitude was below the minimum altitude of 8300 ft. published at ZZZZZ1. I immediately told the Captain to check altitude and that we were below the published altitude. He commanded a go-around at which point we got a GPWS caution but we were climbing. We called Approach and told them we were going around. We climbed and set up for another approach and landed safely with no issues.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.