Date: 201506
Local time of day: 1801-2400
Location: TTPP.Airport, FO
Flight conditions: VMC
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Flight plan: IFR
Flight phase: Descent; Initial Approach
ATC / advisory: Center TTZP
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness
Anomaly: Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Detector: Automation Aircraft Terrain Warning; Person Flight Crew
When detected: In-flight
Result: Flight Crew Took Evasive Action; Flight Crew Became Reoriented
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: This event occurred during descent into Port of Spain; Trinidad. First Officer (FO) briefed a RNAV (GPS) approach to runway 10 in visual conditions at night. We planned the approach in VNAV and LNAV. He briefed a possible late descent by approach control and the high terrain to the north of the airport; as well as the MEAs and MSA on the arrival. I went to terrain display while he initially stayed on weather since we were still above clouds at altitude. Approaching top of descent we requested descent clearance. We were cleared to descend; and the FO began the descent in Level change since we were a little high after the clearance. Initial clearance was FL170 then FL110. We were then cleared to descend to 4;100 feet and cleared for the RNAV approach to runway 10. Between ITRAK and OMEGO we decided to set 2;500 feet for the altitude at the IAF LEXOR in case we got the procedure hold at LEXOR. We decided to ask approach whether we could expect to enter the hold; and were told to expect no delays. FO then removed the hold from the FMC. That caused path indicator to disappear while it recalculated. We were in visual conditions with the terrain in sight and visually clear of terrain. I think that lulled us into focusing more on flying visually rather than cross checking the instruments and automation. We were not in VNAV (at what point that occurred I don't know); and while distracted we continued to descent below the MEA (4;100) to 3;000 before we caught our error. We immediately leveled at 3;000 and quickly decided to stay there rather than climb because we were near OMEGO where the altitude changed to 3;000 and we were VMC and clear of terrain. We then got a GPWS terrain pull up warning. The FO immediately disconnected the autopilot and executed the escape maneuver. Right after beginning the maneuver the warnings ceased. We then resumed the arrival and approach without incident executed a stable approach and landing.We debriefed after gate arrival; and concurred that we had made obvious errors during the arrival. We discussed how we could have let it get to the point where we were well below the route altitude. We had both been shocked and surprised by the GPWS when it appeared that we were clear of terrain. However; we realize that we would never have gotten the warning if we had flown the approach as depicted. It was a very hard lesson to learn and very humbling.




Synopsis: B737 Captain experienced a GPWS terrain warning during a night visual approach to TTPP Runway 10 from the north. The aircraft was in Level Change with 3;000 feet set in the MCP altitude window and 3;000 feet was reached prior to OMEGO. Evasive action was taken; with only a small climb required to cancel the warning; then the approach was continued.