What was found
FIRST OFFICER AND SIC WERE CONDUCTING A REPOSITION FLIGHT FROM KGKY TO KADS. ON APPROACH AND CONFIGURED AIRCRAFT FOR LANDING, AN EICAS MESSAGE INDICATED HYD QTY A SYS LOW. IMMEDIATELY AFTER, SIC OBSERVED PTU MAKING ABNORMAL NOISE. FO THE PIC TO RUN THE APPROPRIATE CHKLST WHILE FO IMMEDIATELY PULLED THE PTU CIRCUIT BREAKER. FOLLOWING, ADDITIONAL EICAS MESSAGES APPEARED, INCLUDING HYD PTU FAIL, HYD PUMP FAIL A, & AILERON RATIO LOW. HYD SYS SYNOPTIC CONFIRMED SYS A PRESSURE AT 0 PSI WITH QTY REDUCED TO 2. DIVERTED TO KAFW. CONTACTED ADDISON TOWER, BROKE OFF THE APPROACH, & DECLARED AN EMERGENCY. HANDED OFF TO APPROACH CONTROL & RECEIVED RADAR VECTORS TOWARD KAFW. LANDED SAFELY WITH NO FURTHER ISSUES. ACFT INSPECTED ON THE RUNWAY, SECURED, & TOWED CLEAR FOR FURTHER INSPECTION AND REPAIR.