B747-400
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Flight Engineer; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 150; Flight Crew Total 6000; Flight Crew Type 1600
Human-Machine Interface
Deviation - Altitude Overshoot; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter CFTT / CFIT; Inflight Event / Encounter Weather / Turbulence
Air Traffic Control Issued Advisory / Alert; Flight Crew Returned To Clearance
Weather; Human Factors
During a trans-Pacific flight to ANC [while] on approach vectors; we were cleared to descend to 1;600 FT in continuous light to moderate turbulence. I believe the heading was 050 to intercept the LOC to [Runway] 07R. The First Officer was hand flying. I was working the radio; MCP; flaps and FMS selections. Around 2;000 FT we began to go from moderate to severe turbulence. The First Officer inadvertently overshot the altitude to about 1;200 FT. I was distracted from instrument monitoring due to MCP and flap selections. The First Officer also mentioned loss of airspeed; windshear; of approximately 20 KTS. Approach Control drew attention to our altitude as I was about to report the turbulence. The First Officer corrected back to 1;600 FT. I also said we had the airport in sight and accepted the visual approach. The turbulence returned to light to moderate and I gave another PIREP. We landed with no further problems. As typical; everything seemed to happen at the same time.
Moderate to severe turbulence during their approach for landing contributed to a descent below their cleared altitude and an altitude warning from ATC for a B747-400 flight crew.