Narrative:

Our flight was dispatched from ZZZ to ZZZ1. Departure from ZZZ was on [runway] xxr with an overcast layer and turbulent air due to recent weather passage. Prior to departure; I called dispatch to discuss the rides and potential for the F/as (flight attendants) to be up in cruise and I concluded that this would be ill-advised. F/as were briefed that we would not be serving on this flight and to remain seated due to turbulence. Passengers were briefed of the turbulence and plan of no service. We climbed to our cruise altitude of FL340 with minor deviations around the weather in the ZZZ area. The ride at FL340 was intermittent light chop but degraded to continuous light chop occasional light to moderate turbulence as we began our descent into ZZZ1.I was the PF (pilot flying) on this leg and the ZZZ1 ATIS indicated that instrument approaches were in use. I briefed the runway xxr Z ILS which was indicated as the approach in use. Courses were set and localizer frequencies were tuned and in the primary position on the navigation radios. We were slowed to 210 knots and given descent from 11;000 feet to eventually to 3;000 feet. I called for flaps 5 to aid in descent. We were told to expect a ten-mile final. It appeared we were next for the approach. Cloud tops were somewhere in the vicinity of 5;000 feet. Intercept heading for the localizer and approach clearance were issued as I was slowing to 170 knots on the base leg. VOR/localizer was armed and I verbalized this. As we intercepted the localizer; the aircraft turned inbound on course; shortly followed by an amber cws-right (control wheel steering-roll) indication on the navigation display. We both saw this immediately and I selected heading mode and a slight left heading adjustment to steer back to the localizer as we were drifting slightly right of course. We were perhaps two to three miles outside the FAF at this point. We both looked to try to identify why the autopilot disconnection had occurred and I noticed that my navigation frequency had been flipped to the standby frequency. The ILS xxr Z frequency was flipped back to primary as we approached the FAF still in heading mode. Approach was selected and; to aid in capture of the localizer/glideslope. I disconnected the autopilot and autothrottles. I called for landing gear down; flaps 15 and V/south (vertical speed) mode down 500 to catch the glideslope as we were trending high. We were also left of course.we started down and descended perhaps 800 feet when the pm (pilot monitoring) stated that we were left of course. I made a heading correction back to the right; but shortly thereafter stated that this was not going to work and called go-around; flaps 15 and advanced the thrust. Landing gear was retracted; flaps retracted on schedule and a climb to 3;000 feet was initiated. We notified the tower of our go-around and they asked for the reason. We stated an instrumentation error. We were given instructions to climb to 4;000 feet and given a right crosswind heading and told to contact departure.I climbed to 4;000 feet and re-engaged the autopilot. After checking in with approach; we were instructed this was 'vectors for the ILS xxr Z - confirm Z...' we received a downwind heading and 210 knots speed assignment. Base turn and descent to 3;000 feet were issued and 3;000 feet was set and confirmed in the MCP (mode control panel). As I recall; I selected lvl chg and verbalized setting 180 knots as we descended. I must have been manually operating the thrust levers as we descended because later we realized the autothrottles were not engaged.vector to intercept and approach clearance was issued. VOR/localizer was armed and verbalized. As we began to level at 3;000 feet the pm said something to the effect of; 'hey; we need some flaps' and I immediately called for flaps 5 (I must have neglected to call for flaps when I set speed to 180 in lvl chg). As the aircraft was leveling and intercepted the localizer in the turn; almost coincident with flap extension; thestick-shaker went off. I immediately applied firewall thrust; called for emergency thrust and disconnected the autopilot and autothrottles. As the flaps deployed and power rapidly came in; we climbed 800 feet to 900 feet on-course; on the localizer. The stick shaker was activated for perhaps 2-3 seconds. As I reacted to the startle of the moment; I stated 'I think we may need to go around again;' but after quickly discussing it with the pm we determined we were still seven to eight miles from the FAF and on-course; slightly above the gsia.thrust was reduced to maintain altitude; the autopilot and autothrottles were re-engaged and appch was selected. At this moment I looked out the L1 window to see a significant amount of mixed ice; perhaps 1-1/2 inch on my windshield wiper (engine anti-ice was on but wing anti-ice was not; as I was unaware of any icing reports in cloud). I immediately turned on wing anti-ice. Localizer and G/south were captured; normal configuration/approach/landing were accomplished on runway xxr. Additionally; large chunks of ice flaked off from the windshield wiper and radome as we exited the base of the clouds.after shutting down at the gate we attempted to reconstruct what happened. The entire sequence of events had started with the loss of localizer guidance after intercept. I couldn't understand how my localizer frequency was not tuned correctly (and no amber localizer indication on either of our pfds indicating mistuning). I know for a fact that I tuned it and transferred to the active position during my brief. However; after physically touching the transfer button on my radio head while at the gate; I realized that if the button was touched just slightly - not pressed to the detent - that the frequency would flip! Simply brushing your hand across the button changed the frequency. All I can figure is that when the aircraft intercepted the localizer and was decelerating; I must have brushed my hand across the button - perhaps re-trimming the rudder; which is not unusual for me to do as the aircraft is re-configured.pm was out of his element on this trip. He is a total pm flyer and admitted having great difficulty being alert on this am trip which included very early am show times.

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Original NASA ASRS Text

Title: B737 flight crew reported that the stick-shaker went off during flaps extension on descent; while the radio frequency switched and the autopilot disconnected on approach.

Narrative: Our flight was dispatched from ZZZ to ZZZ1. Departure from ZZZ was on [Runway] XXR with an overcast layer and turbulent air due to recent weather passage. Prior to departure; I called Dispatch to discuss the rides and potential for the F/As (Flight Attendants) to be up in cruise and I concluded that this would be ill-advised. F/As were briefed that we would not be serving on this flight and to remain seated due to turbulence. Passengers were briefed of the turbulence and plan of no service. We climbed to our cruise altitude of FL340 with minor deviations around the weather in the ZZZ area. The ride at FL340 was intermittent light chop but degraded to continuous light chop occasional light to moderate turbulence as we began our descent into ZZZ1.I was the PF (Pilot Flying) on this leg and the ZZZ1 ATIS indicated that instrument approaches were in use. I briefed the Runway XXR Z ILS which was indicated as the approach in use. Courses were set and localizer frequencies were tuned and in the primary position on the NAV radios. We were slowed to 210 knots and given descent from 11;000 feet to eventually to 3;000 feet. I called for flaps 5 to aid in descent. We were told to expect a ten-mile final. It appeared we were next for the approach. Cloud tops were somewhere in the vicinity of 5;000 feet. Intercept heading for the localizer and approach clearance were issued as I was slowing to 170 knots on the base leg. VOR/LOC was armed and I verbalized this. As we intercepted the localizer; the aircraft turned inbound on course; shortly followed by an amber CWS-R (Control Wheel Steering-Roll) indication on the NAV display. We both saw this immediately and I selected heading mode and a slight left heading adjustment to steer back to the localizer as we were drifting slightly right of course. We were perhaps two to three miles outside the FAF at this point. We both looked to try to identify why the autopilot disconnection had occurred and I noticed that my NAV frequency had been flipped to the standby frequency. The ILS XXR Z frequency was flipped back to primary as we approached the FAF still in heading mode. APCH was selected and; to aid in capture of the localizer/glideslope. I disconnected the autopilot and autothrottles. I called for landing gear down; flaps 15 and V/S (Vertical Speed) mode down 500 to catch the glideslope as we were trending high. We were also left of course.We started down and descended perhaps 800 feet when the PM (Pilot Monitoring) stated that we were left of course. I made a heading correction back to the right; but shortly thereafter stated that this was not going to work and called go-around; flaps 15 and advanced the thrust. Landing gear was retracted; flaps retracted on schedule and a climb to 3;000 feet was initiated. We notified the Tower of our go-around and they asked for the reason. We stated an instrumentation error. We were given instructions to climb to 4;000 feet and given a right crosswind heading and told to contact Departure.I climbed to 4;000 feet and re-engaged the autopilot. After checking in with Approach; we were instructed this was 'vectors for the ILS XXR Z - confirm Z...' We received a downwind heading and 210 knots speed assignment. Base turn and descent to 3;000 feet were issued and 3;000 feet was set and confirmed in the MCP (Mode Control Panel). As I recall; I selected LVL CHG and verbalized setting 180 knots as we descended. I must have been manually operating the thrust levers as we descended because later we realized the autothrottles were not engaged.Vector to intercept and approach clearance was issued. VOR/LOC was armed and verbalized. As we began to level at 3;000 feet the PM said something to the effect of; 'Hey; we need some flaps' and I immediately called for flaps 5 (I must have neglected to call for flaps when I set speed to 180 in LVL CHG). As the aircraft was leveling and intercepted the localizer in the turn; almost coincident with flap extension; thestick-shaker went off. I immediately applied firewall thrust; called for emergency thrust and disconnected the autopilot and autothrottles. As the flaps deployed and power rapidly came in; we climbed 800 feet to 900 feet on-course; on the localizer. The stick shaker was activated for perhaps 2-3 seconds. As I reacted to the startle of the moment; I stated 'I think we may need to go around again;' but after quickly discussing it with the PM we determined we were still seven to eight miles from the FAF and on-course; slightly above the GSIA.Thrust was reduced to maintain altitude; the autopilot and autothrottles were re-engaged and APPCH was selected. At this moment I looked out the L1 window to see a significant amount of mixed ice; perhaps 1-1/2 inch on my windshield wiper (engine anti-ice was on but wing anti-ice was not; as I was unaware of any icing reports in cloud). I immediately turned on wing anti-ice. LOC and G/S were captured; normal configuration/approach/landing were accomplished on Runway XXR. Additionally; large chunks of ice flaked off from the windshield wiper and radome as we exited the base of the clouds.After shutting down at the gate we attempted to reconstruct what happened. The entire sequence of events had started with the loss of localizer guidance after intercept. I couldn't understand how my localizer frequency was not tuned correctly (and no amber Localizer indication on either of our PFDs indicating mistuning). I know for a fact that I tuned it and transferred to the active position during my brief. However; after physically touching the transfer button on my radio head while at the gate; I realized that if the button was touched JUST SLIGHTLY - not pressed to the detent - that the frequency would flip! Simply brushing your hand across the button changed the frequency. All I can figure is that when the aircraft intercepted the Localizer and was decelerating; I must have brushed my hand across the button - perhaps re-trimming the rudder; which is not unusual for me to do as the aircraft is re-configured.PM was out of his element on this trip. He is a total PM flyer and admitted having great difficulty being alert on this AM trip which included very early AM show times.

Data retrieved from NASA's ASRS site 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.