What was found
AFTER DEPARTURE AT APPROXIMATELY 1,000 FT A-SYSTEM HYDRAULICS AND FEEL DIFFERENTIAL LIGHT ILLUMINATED, TURNED BACK TO PHX, FLIGHT CONTROLS FELT STIFF BUT FUNCTIONAL. MAINTENANCE FOUND A-SYSTEM FLIGHT CONTROL MODULAR PACKAGE FAULTING, REPLACED MODULAR PACKAGE IAW BMM 27-09-21, OPS CHECK GOOD. FAILURE ANALYSIS TEST OF FLIGHT CONTROL MODULAR PACKAGE AND COULD NOT FIND ANY DEFECTS IN UNIT. A FULL FUNCTIONAL TEST WAS ACCOMPLISHED PER BOEING DWG 65-44891 REV. E, WITH NO DEFECTS NOTED. UNIT WAS DISASSEMBLED AND THE ONLY DEFECT FOUND WAS A SWOLLEN, SLIGHTLY DISTORTED O-RING SEAL ON POPPET ASSEMBLY FOR COMPENSATOR UNIT. (CLOSED)