Regional Jet 900 (CRJ900)
Flight Crew Commercial
Flight Crew Last 90 Days 122
Confusion; Situational Awareness
Aircraft Equipment Problem Less Severe; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Flight Crew Overcame Equipment Problem; Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Aircraft; Human Factors
After being cleared for the ILS XX in ZZZ; I initiated a descent to 1;600 ft. and began slowing from 250 kts. On the left downwind just past ZZZZZ the aircraft made an unprompted right turn away from its present course. The aircraft was in heading mode and I (FO) attempted to correct the course deviation with the heading bug but the autopilot was unresponsive. The GPWS went off with a caution message due to the terrain south of the field. The CA then took manual control and initiated a climb away from the terrain and back on an intercept course. The GPWS and Radar Altimeter (RA) sounded another caution on the intercept back to the ILS even though there was no terrain present. The CA initiated another climb and then resumed course. He asked me to configure the aircraft for the approach and then handed back controls for me. The approach was then completed in a stabilized and safe manner with no further incident. The initial error was a malfunction with the aircraft turning right unprompted but the human error was the PF (FO) not disengaging the autopilot immediately and instead allowing the situation to degrade into a GPWS caution. Much of the situation could have been avoided if the autopilot was disengaged and the approach hand-flown instead of a reliance on automation. The terrain was briefed initially but I lost situational awareness of its location on the downwind. The mistake won't be made again.
CRJ900 First Officer reported receiving a GPWS alert while on a downwind vector for an ILS approach.