Narrative:

During approach to tus; leg 5 of a 6-leg day; talking to approach control; we were cleared direct calls for the ILS 11L and cleared to descend to 5;000 ft. We called the airport in sight and were cleared for the visual approach and told to contact tower. First officer selected direct pocib in the FMC; and selected 4;600 ft on the MCP. When we contacted tower; the controller said to check altitude and stated the MVA in the area was 5;900 ft. Simultaneously we received a 'caution terrain; caution obstacle' alert from the GPWS. First officer executed go-around maneuver. We climbed to clear the alert. Once we were clear of the hazard; we continued our descent to the runway. An s-turn to the south was needed to lose altitude. The terrain feature was in use on both navigation displays; but did not show an immediate threat in front of the airplane. The turn to pocib was not verbalized; but I was aware of it. This turn only changed our lateral course by a couple of degrees to the right; so I did not initially think it would make a big difference; but it apparently brought us close enough laterally to terrain to trigger the alert.[we needed] verbalization of changes to FMC programming; staying on previously cleared path and altitude at night; even when cleared for a visual approach; especially in mountainous areas. Better monitoring and situational awareness on the part of the captain/pilot not flying; not trying to salvage the approach under such conditions.

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Original NASA ASRS Text

Title: B737 flight crew experiences an EGPWS terrain caution just after a low altitude alert from the Tower during a night visual approach to Runway 11L at TUS. An immediate climb is initiated.

Narrative: During approach to TUS; leg 5 of a 6-leg day; talking to Approach Control; we were cleared direct CALLS for the ILS 11L and cleared to descend to 5;000 FT. We called the airport in sight and were cleared for the visual approach and told to contact Tower. First Officer selected direct POCIB in the FMC; and selected 4;600 FT on the MCP. When we contacted Tower; the Controller said to check altitude and stated the MVA in the area was 5;900 FT. Simultaneously we received a 'Caution Terrain; Caution Obstacle' alert from the GPWS. First Officer executed go-around maneuver. We climbed to clear the alert. Once we were clear of the hazard; we continued our descent to the runway. An s-turn to the south was needed to lose altitude. The terrain feature was in use on both navigation displays; but did not show an immediate threat in front of the airplane. The turn to POCIB was not verbalized; but I was aware of it. This turn only changed our lateral course by a couple of degrees to the right; so I did not initially think it would make a big difference; but it apparently brought us close enough laterally to terrain to trigger the alert.[We needed] verbalization of changes to FMC programming; staying on previously cleared path and altitude at night; even when cleared for a visual approach; especially in mountainous areas. Better monitoring and situational awareness on the part of the Captain/pilot not flying; not trying to salvage the approach under such conditions.

Data retrieved from NASA's ASRS site as of July 2013 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.