Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 200; Flight Crew Type 10000
Human-Machine Interface; Situational Awareness
Deviation / Discrepancy - Procedural Other / Unknown; Inflight Event / Encounter Weather / Turbulence
Human Factors; Weather; Aircraft
Intermittent stick shaker on turn to final. Conditions: ILS approach required for ceiling and visibility; blowing snow; wind shear reported on ATIS; braking action good reported by Tower; strong winds aloft; approximately 50 KTS at 2;000 FT AGL (approximately 200 degrees at 50 KTS). Icing conditions on descent and arrival. Engine anti-ice on and wing anti-ice used several times before starting approach (changes stick shaker logic). Autopilot and autothrottles engaged during event. Event Description: ATC usually gives a base turn and then a last vector to final to intercept the Localizer. This night we received a left turn to intercept the Localizer of approximately 120 degrees. The aircraft was clean; airspeed bug approximately four knots above [maneuver] speed. Bank angle set 30 degrees. In the turn; we encountered continuous moderate turbulence. I was the pilot flying with hands on the controls monitoring the automation. In the turn; we received several intermittent bank angle alerts and one intermittent stick shaker that lasted about one second just prior to localizer intercept. The autopilot was managing aircraft control; however; I did not set the automation in a state that allowed enough of a buffer to handle the turbulence with 30 degrees bank at current airspeed. Approach was armed after localizer capture. The automation was used to configure for approach and then disconnected in order the control airspeed on final approach. Wind shear plus/minus 15 KTS encountered during approach which was not relayed by proceeding aircraft. Other areas which increased risk this day were: Crew Scheduling of over eight hours flight time per new regulations; last flight of day running late; first flight with First Officer; fourth First Officer flown within two days. Select a higher speed to increase stall margin in turbulent conditions or select flaps 1 or flaps 5 and fly above bugged speed to increase stall margin. Reduce bank angle during turbulent conditions to increase stall margin; accepting flight path through localizer if needed. Approach could have given us several turns to final which would have made the final intercept less challenging for the current winds and conditions.
B737-700 Captain experiences stick shaker during the turn to intercept the localizer in the clean configuration; along with intermittent bank angle annunciations; in turbulent conditions. Speed had been set at clean maneuver plus five KTS.