As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
BWI - FLT 1555 - THE AIRCRAFT LOST THE 'A' SYSTEM HYDRAULIC QUANTITY SHORTLY AFTER TAKEOFF FROM BWI. THE AIRCRAFT WAS RETURNED TO BWI WHERE IT LANDED WITHOUT INCIDENT. MAINTENANCE FOUND THE 'A' SYSTEM HYDRAULIC MANUAL SHUT-OFF VALVE IN THE TAIL COMPARTMENT LEAKING. THE VALVE WAS REMOVED AND REPLACED. LEAK AND OPERATIONAL CHECKS WERE GOOD. (X)