B757-200
Flight Crew Air Transport Pilot (ATP)
Situational Awareness
Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT; Inflight Event / Encounter Unstabilized Approach
Flight Crew Became Reoriented
Human Factors
At approximately 1;200 MSL; I broke off the ILS to 22R and began my circling maneuver to Runway 29. Runway 29 had been programmed into the FMCS with a 5 nm runway extension. On downwind ATC directed us to start our base turn inside the 5 mile fix. Once established on base leg; I could not see the runway from my seat; so I started a turn toward the runway and began a gradual descent. Since much of my attention was devoted to trying to locate the runway; I descended lower than I intended. When the GPWS obstacle warning sounded; we initiated a go-around and landed on 22R. In my 14 years as Captain on the 757; this was my first circle to land maneuver. In hindsight; I would have made a three mile fix and [used] LNav to the fix.
A B757-200 received a GPWS terrain warning on a circling approach when it descended below procedure altitude. A climb to a safer altitude and a normal landing was made.