B737 Undifferentiated or Other Model
Flight Crew Total 2216
Confusion; Situational Awareness
Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT; Inflight Event / Encounter Unstabilized Approach; Inflight Event / Encounter Weather / Turbulence
Flight Crew Became Reoriented
Human Factors
On final approach we had GPWS terrain Caution and shortly after a GPWS obstacle caution. We were doing the RNAV Approach. Captain had decided on a flaps 40 landing due to rain that had recently moved through the area. There was a small rain shower on final between the end of the runway and the final approach fix. Ceilings were appx 1;000. When we were initially cleared for the approach I set the final approach fix altitude and verified that LNAV and VNAV Path were both engaged. Crossing the initial fix we then set 100 feet and proceeded on the approach. At 1;000 I called approaching minimums and runway in sight. Right after that we got the GPWS Terrain Caution. I called GPWS Terrain Caution Climb. At that point the Captain arrested the descent and made a climb back to the approach path and continued to landing since we could visually verify the aircraft position and return to approach path. I looked at the FMA and for some reason we were now in level change. I am not sure when that change took place as when I set the 100 feet we were in LNAV and VNAV Path if I remember correctly. I pointed out to the captain that some how we were in level change. My best guess is that somehow by being in level change we slipped under the flight path designated by the GPS. My only thought is that perhaps the speed window was opened in an attempt to adjust the approach speed except instead of the speed window level change was perhaps selected. I do not remember the captain announcing that he was opening the window or adjusting the speed. I am purely speculating as to how the wrong mode could be selected that close to the ground. Flight Operations Quality Assurance (FOQA) data might be able to provide more clarity as to when and what was selected.
B737 flight crew approaching minimums on an RNAV approach a crew received a GPWS terrain caution. The crew climbed back to the correct the approach path and landed.