Narrative:

We were IMC and descending to 8000 ft on vectors to intercept runway 25L localizer. Airplane was in a clean confign and autoplt and autothrottles were engaged. Heading select was lateral mode; level change was vertical mode and autothrottles were at idle and in arm mode. ATC gave a clearance to proceed direct prino to intercept localizer. Captain entered prino in the FMS and selected LNAV. A number of things happened in quick succession and nearly simultaneously: 1) autoplt banked left to comply with prino clearance. 2) autoplt leveled off at 8000 ft and autothrottles began advancing. 3) we entered an area of what felt like moderate wake turbulence and the airspeed rolled back 20 KTS to 190 KIAS. 4) stick shaker activated followed shortly by stall buffet. 5) aircraft continued to roll sharply left to about 60 degrees bank. This was exacerbated by the fact that the #2 engine spun up much faster than #1 engine (we had noted this on takeoff roll) as the autothrottles tried to regain the 210 KT bug speed.supplemental information from acn 643095: aircraft had #2 anti-ice cowl valve wired open. I was PF. We were solid IMC in icing regime. I was attempting to maintain 60% N1 due to open valve. We descended from 9000 ft MSL to 8000 ft MSL on vectors to las runway 25L localizer; about 20-25 NM out; clean confign; 210 KIAS; autoplt on and; I believe; autothrottle on (level change mode). Aircraft went into 30 degree left bank (I believe it was turning to princ). Suddenly there were several quick jolts in pitch and roll; as if we were in moderate wake turbulence. At the same time; I saw 190 KIAS (clean speed is approximately 180 KIAS); in quick succession (as I remember) I added power to regain 210 KIAS. The aircraft then quickly rolled further in a left bank to 60 degrees. Stick shaker briefly activated twice with some buffet. As this was happening; I overrode autoplt with right aileron. Aircraft was in a slight descent and I applied some pitch to limit loss to 250 ft without reactivating stick shaker. The aircraft quickly rolled wings level and accelerated to approximately 230 KIAS as we climbed back to 8000 ft. Causes/guesses: I had to divert attention to navigating as mode control unit is on captain's side only. I did not see initial airspeed decrease from 210 KTS to 190 KIAS at 30 degrees bank; wake turbulence coupled by left roll from engine spool up increased bank to 60 degrees to probably increased stall warning speed. Leading to stall warning during recovery maneuver.

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Original NASA ASRS Text

Title: A B737-300 CREW EXPERIENCED STALL WARNING WHILE ENCOUNTERING WAKE TURB ON THE FINAL APCH INTERCEPT TURN.

Narrative: WE WERE IMC AND DSNDING TO 8000 FT ON VECTORS TO INTERCEPT RWY 25L LOC. AIRPLANE WAS IN A CLEAN CONFIGN AND AUTOPLT AND AUTOTHROTTLES WERE ENGAGED. HDG SELECT WAS LATERAL MODE; LEVEL CHANGE WAS VERT MODE AND AUTOTHROTTLES WERE AT IDLE AND IN ARM MODE. ATC GAVE A CLRNC TO PROCEED DIRECT PRINO TO INTERCEPT LOC. CAPT ENTERED PRINO IN THE FMS AND SELECTED LNAV. A NUMBER OF THINGS HAPPENED IN QUICK SUCCESSION AND NEARLY SIMULTANEOUSLY: 1) AUTOPLT BANKED L TO COMPLY WITH PRINO CLRNC. 2) AUTOPLT LEVELED OFF AT 8000 FT AND AUTOTHROTTLES BEGAN ADVANCING. 3) WE ENTERED AN AREA OF WHAT FELT LIKE MODERATE WAKE TURB AND THE AIRSPD ROLLED BACK 20 KTS TO 190 KIAS. 4) STICK SHAKER ACTIVATED FOLLOWED SHORTLY BY STALL BUFFET. 5) ACFT CONTINUED TO ROLL SHARPLY L TO ABOUT 60 DEGS BANK. THIS WAS EXACERBATED BY THE FACT THAT THE #2 ENG SPUN UP MUCH FASTER THAN #1 ENG (WE HAD NOTED THIS ON TKOF ROLL) AS THE AUTOTHROTTLES TRIED TO REGAIN THE 210 KT BUG SPD.SUPPLEMENTAL INFO FROM ACN 643095: ACFT HAD #2 ANTI-ICE COWL VALVE WIRED OPEN. I WAS PF. WE WERE SOLID IMC IN ICING REGIME. I WAS ATTEMPTING TO MAINTAIN 60% N1 DUE TO OPEN VALVE. WE DSNDED FROM 9000 FT MSL TO 8000 FT MSL ON VECTORS TO LAS RWY 25L LOC; ABOUT 20-25 NM OUT; CLEAN CONFIGN; 210 KIAS; AUTOPLT ON AND; I BELIEVE; AUTOTHROTTLE ON (LEVEL CHANGE MODE). ACFT WENT INTO 30 DEG L BANK (I BELIEVE IT WAS TURNING TO PRINC). SUDDENLY THERE WERE SEVERAL QUICK JOLTS IN PITCH AND ROLL; AS IF WE WERE IN MODERATE WAKE TURB. AT THE SAME TIME; I SAW 190 KIAS (CLEAN SPD IS APPROX 180 KIAS); IN QUICK SUCCESSION (AS I REMEMBER) I ADDED PWR TO REGAIN 210 KIAS. THE ACFT THEN QUICKLY ROLLED FURTHER IN A L BANK TO 60 DEGS. STICK SHAKER BRIEFLY ACTIVATED TWICE WITH SOME BUFFET. AS THIS WAS HAPPENING; I OVERRODE AUTOPLT WITH R AILERON. ACFT WAS IN A SLIGHT DSCNT AND I APPLIED SOME PITCH TO LIMIT LOSS TO 250 FT WITHOUT REACTIVATING STICK SHAKER. THE ACFT QUICKLY ROLLED WINGS LEVEL AND ACCELERATED TO APPROX 230 KIAS AS WE CLBED BACK TO 8000 FT. CAUSES/GUESSES: I HAD TO DIVERT ATTN TO NAVING AS MODE CTL UNIT IS ON CAPT'S SIDE ONLY. I DID NOT SEE INITIAL AIRSPEED DECREASE FROM 210 KTS TO 190 KIAS AT 30 DEGS BANK; WAKE TURB COUPLED BY L ROLL FROM ENG SPOOL UP INCREASED BANK TO 60 DEGS TO PROBABLY INCREASED STALL WARNING SPD. LEADING TO STALL WARNING DURING RECOVERY MANEUVER.

Data retrieved from NASA's ASRS site as of January 2009 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.