Gulfstream IV flight crew reported while on autopilot the aircraft turned the wrong direction during an approach. While attempting to recover; the aircraft descended below the assigned altitude and flew below the Minimum Vectoring Altitude.
Synopsis
Gulfstream IV flight crew reported while on autopilot the aircraft turned the wrong direction during an approach. While attempting to recover; the aircraft descended below the assigned altitude and flew below the Minimum Vectoring Altitude.
Narrative
Enroute to ZZZ from ZZZ1; we requested LOC XX approach with Approach Control and were given approach clearance from ZZZ2 to ZZZZZ. As we passed ZZZ2 in a descent approaching ZZZZZ at 14;000 ft.; our NAV system took a hard right turn to the east as if it was not going to capture the 4 DME arc at ZZZZZ. Lateral and vertical modes were: LNAV/VNAV with Autopilot engaged at the time. As we passed ZZZZZ; I intervened by selecting heading mode as the active lateral guidance. As such; the aircraft's descent mode defaulted to VFLCH and the aircraft kept descending through 14;000 ft. at ZZZZZ (MDA of 8;760 ft.) We were anticipating LNAV/VNAV guidance to a visual approach for Runway XX.By the time we started a turn back to the north towards ZZZZZ1; and arresting the descent; we had descended to an altitude of about 13; 600 ft.ATC noticed our turn to the east and altitude; giving a turn to an XXX degree heading and climb instructions back to 14;000 ft. On assigned heading and altitude; ATC informed us about the minimum altitude in that area and subsequently cleared us direct to ZZZZZ2 to intercept the approach. From ZZZZZ2 the approach and landing were uneventful.
Second reporter narrative
Enroute to ZZZ from ZZZ1; we requested LOC XX approach with Approach Control and were given approach clearance from ZZZ2 to ZZZZZ. As we passed ZZZ2 in a descent approaching ZZZZZ at 14;000 ft. our NAV system took a hard right turn to the east as if it was not going to capture the 4 DME arc at ZZZZZZ. Lateral and vertical modes were: LNAV/VNAV with Autopilot engaged at the time. As we passed ZZZZZ; I intervened by selecting Heading Mode as the active lateral guidance. As such; the aircraft's descent mode defaulted to VFLCH and the aircraft kept descending through 14;000 ft. at ZZZZZ (MDA of 8;760 ft.) We were anticipating LNAV/VNAV guidance to a visual approach for Runway XX. By the time we started a turn back to the north towards ZZZZZ1; and arresting the descent; we had descended to an altitude of about 13;600 ft. ATC noticed our turn to the east and altitude; giving a turn to a XXX degree heading and climb instructions back to 14;000 ft. After established on assigned heading and altitude; ATC informed us about the MVA in that area and subsequently cleared us direct to ZZZZZ2 to intercept the approach. From ZZZZZ2 the approach and landing were uneventful.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.