As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PHL-DEN - EMERGENCY LANDING - WHILE EN ROUTE PHL-DEN, CREW RECEIVED YELLOW HYDRAULIC SYSTEM LOW PRESSURE AND LOW QUANTITY CAUSED BY PTU RUNNING CONTINUOUSLY. YELLOW QUANTITY DROPPED TO ZERO, CREW DECLARED AN EMERGENCY AND DIVERTED TO PIT. MAINTENANCE REMOVED AND REPLACED THE HYDRAULIC POWER TRANSFER UNIT IAW AIRBUS MAINTENANCE MANUAL 29-23-41.