What was found
(CAN) ON DECENT NR1 A SYS LOW PRESSURE LIGHT ILLUMINATED. SHORTLY, NR 2 A SYS LOW PRESSURE LIGHT ILLUM. CREW ACCOMPLISHED QRH FOR LOSS OF SYS A. EMERGENCY DECLARED & LANDED. MAINT CHECKED SERVICEABLE HYD SYS RES STANDPIPE & PRESSURE. ENG RAN AND HYD PRESSURE SERVICEABLE AT 3000 PSI. MAINT SUSPECTED PRESSURE RELIEF VALVE IN A SYS PRESSURE MODULE TO BE AT FAULT. A SYS PRESSURE MODULE REPLACED AND GROUND RUNS SATISFACTORY. AC RELEASED FOR SERVICE. TO PERFORM A FULL INSP AND FUNCTION OF RESERVOIR AIR PRESSURE SYS TO ENSURE FAULT WAS NOT CAUSED BY CAVITATING PUMPS DUE TO HEAD PRESSURE LOSS.