As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PHX - AIR TURNBACK - 6/5/01 - FLT 253 - EN ROUTE TO PHL ECAM MSG DISPLAYED HYD YELLOW SYS LOW LEVEL; YELLOW HYD QUANTITY INDICATED IN THE AMBER BAND; CREW COMPLIED W/ THE ECAM ACTIONS & RETURNED TO PHX MAKING AN UNEVENTFUL LANDING. MX INSPECTED THE A/C AND FOUND THE YELLOW HYD SYS LEAK MEASUREMENT VALVE, PILOT VALVE LEAKING; THE PILOT VALVE WAS REPLACED, THE YELLOW SYS WAS SERVICED AND LEAK CHECKS AND FUNCTIONAL CHECKS WERE GOOD IAW AMM 29-19-51-401.