B747-400
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 150; Flight Crew Total 14500; Flight Crew Type 7800
Workload; Confusion; Distraction; Time Pressure; Communication Breakdown
Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Flight Crew Executed Go Around / Missed Approach; Flight Crew Took Evasive Action
ATC Equipment / Nav Facility / Buildings; Weather; Procedure; Human Factors
On vectors to the RNAV approach; Controller gave us direct the initial waypoint as a base leg; [and] then before we got to it he turned us inside of it. The non flying pilot accidentally put the initial approach waypoint over top of final approach waypoint; thereby removing it from the approach. I saw this; he said he was going to fix it but he did not have time to put it back in between ATC calls and configuring aircraft to land and turbulence. Inside of initial waypoint we descended to 2;200 FT MSL; waited for the vertical path indicator (VPI) to come down. Aircraft was in LNAV/VNAV autopilot ON; set minimums 1;100 FT MSL in MCP panel. VPI started to come down aircraft followed VPI we saw it was going below the VASI disconnected autopilot started climb. About same time Tower gave us a low altitude alert. Climbed up intercepted the VASI continued visually. About 300-500 FT AGL experienced windshear; did a go-around. Came back around [and] landed. Way to prevent this: Better CRM; confirm all FMC changes before executing change. Also for ATC not to give a direct when on vectors so close to the fix and or then turn you inside of it. ATC could have just as easily could have given us a vector instead of the direct; it would have decreased are work load and minimized FMC changes.
A B747-400 was vectored inside a RNAV initial approach waypoint which the non-flying pilot then put on top the final approach waypoint thus removing it from the approach. At the same time the autopilot VNAV started a descent which generated an ATC low altitude alert followed by a windshear escape maneuver.