What was found
WHILE ON, A-A/P, SELECTED B-A/P. AFTER A FEW SECONDS B-A/P DISENGAGED. THEN A-A/P WOULD NOT ENGAGE. B-A/P WILL ENGAGE BUT DISENGAGE AFTER A FEW SECONDS. NO OTHER SYS PROBLEMS NOTED. ACFT GROUNDED. FAULT REVIEW LAST LEG, BOTH FCC A & B LOGGED SEVERAL ELEVATOR PRESSURE SWITCH-1, FAULTS, 22-11127 AND 22-11535. R & R ELEVATOR PRESSUE SWITCH S771, REF AMM 22-11-40. LEAK & OPS CHECKS NORMAL IAW SAME. ACCOMPLISHED ADDITIONAL LWMP BITE TEST GRP 49 AND HGS SYSTEM TEST, REF AMM 34-36-00, BOTH CHECK NORMAL.