FO OF A JETSTREAM 3100 (LTT) LOST CTL MOMENTARILY WHEN ENCOUNTERING WAKE TURB DURING A VISUAL APCH FOLLOWING A BOEING 737-200 (MLG) 5 MI AHEAD.

Narrative

ON APCH TO MDW (VISUAL TO RWY 31L BACKED UP BY ILS TO RWY 31L) IN A BA 3100 JETSTREAM; VIOLENT ENCOUNTER WITH WAKE TURB FROM PRECEDING BOEING 737-200. THERE WAS A 5 MI SEPARATION BTWN US AND THE 737. THIS WAS CONFIRMED BOTH VISUALLY BY MYSELF AND THE CAPT AND MDW RADAR. WE WERE APPROX 2 MI OUTSIDE THE OM AND ON LOC AND GS. WE COULD SEE THE 737 IN FRONT OF US LOOKED HIGH IN RESPECT TO THE GLIDE PATH. ABOUT THIS TIME; WE ENCOUNTERED A SLIGHT BUFFET. SECONDS LATER; I HAD FULL AILERON DEFLECTION TO THE L AND WAS STILL ROLLING R AT APPROX 10-15 DEGS PER SECOND. ONLY AFTER ABRUPTLY PULLING UP ON THE YOKE TO CLB OUT OF THE ENCOUNTER WAS ACFT CTL ABLE TO BE REGAINED. THE REST OF THE APCH WAS FLOWN APPROX 2 DOTS HIGH ON THE GS AND WE LANDED WITHOUT INCIDENT. FACTORS LEADING TO THIS ARE (IN MY OPINION) AS FOLLOWS: THE B-737 IN QUESTION WAS HIGH ON THE APCH. THE WINGTIP VORTICES WOULD THEN BE ALLOWED TO DSND INTO THE GLIDE PATH WHERE WE ENCOUNTER THEM. TO CORRECT THIS PROB; ACFT -- ESPECIALLY LARGE JET TRANSPORTS -- MUST STAY ON THE PRESCRIBED GLIDE PATH EVEN IN VISUAL CONDITIONS!