What was found
AT 10K FEET B AUTO PILOT WAS ENGAGED. AFTER A FEW SECONDS A FULL LEFT DEFFLECTION OF THE YOKE OCCURED WITH THE B AUTO PILOT DISENGAGING AND THE A/P P/RST RED LIGHTS FLASHING AND AURAL WARNING TONE SOUNDING. GROUNDED - YES. VERIFIED LAST LEG CHAN "B" VNAV SPD LNAV ENG AIL SYNC INV.4 SEC. SUSPECT LRU AIL POS SEN-2 AIL ACT -2 FLT MSG 22-11190. ACCOMP. LRU TEST 20.31 TEST PASS. ALSO ACCOMP. LAND VERIFY TEST, TEST PASS REF. B737-900 M/M 22-11-00-700-801.