What was found
DURING CLIMB OUT, HYD PRESSURE DROPPED TO ZERO, AILERON AND MANUAL REVERSION LIGHTS ILLUMINATED. THE CREW ACCOMPLISHED ALL PROCEDURES IAW QRH, NO LOSS OF HYD QUANTITY. THE CREW RETURNED TO DEPARTURE WITHOUT FURTHER INCIDENT. MX INSPECTED AND REPLACED DUAL FILTERS AND RELIEF VALVE. OPS CHECK GOOD IAW WD 29-01-05, MM 29-10-5, 29-10-18 AND 29-10-16. ACFT WAS RETURNED TO SERVICE.