B737 Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Flight Crew Type 145
Situational Awareness
Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter CFTT / CFIT
Flight Crew Became Reoriented; Flight Crew Took Evasive Action; Flight Crew Returned To Clearance
Human Factors
On initial arrival to MRLB; we planned on an ILS DME Runway 07 approach. This approach was loaded and briefed. Shortly after contact with Liberia approach; we were instructed to expect the VOR DME Runway 25 approach instead. This occurred approximately 15 miles north of the airport. As time was compressed due to our location to the airport; the captain did a cursory brief/load of the new approach. We were cleared to proceed to the LIB VOR; descend to 3000 feet and conduct the VOR DME Runway 25 approach. This was a VFR clear day event. I suggested VNAV as the flight mode to conduct the approach; as well as an airspeed of 180 knots for the course reversal to prevent a large radius turn near rising terrain. After crossing the VOR outbound and on the teardrop procedure turn at 3000 feet; the captain (PF) elected to use V/S mode and slowed the aircraft. Since we were cleared for the approach; level at 3000 feet and inside of the IAF; I asked to set the MCP to 1100 feet (FAF crossing altitude). The PF agreed and I set 1100 feet. LNAV was engaged. At the 10.0 DME outbound point; the captain (PF) chose to leave 3000 feet via V/S and begin a shallow descent to 1100 feet. The procedure does not allow a descent until 10.0 DME inbound to the LIB VOR. The airport was in sight throughout the entire approach. At some point during the course reversal; we received a GPWS alert 'caution terrain' and then a 'pull up' warning. I announced 'stop descending and climb'. The captain (PF) immediately stopped the descent and began a climb. This stopped the warning; we visually confirmed our clearance of terrain; and concluded the approach and landing without incident.
B737 First Officer reported receiving a GPWS 'Terrain; Pull Up' warning on approach to MRLB.