As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: LOSS OF YELLOW HYD SYSTEM INFLIGHT. FOUND BLOWN O-RING ON PTU ISOLATION COUPLING. EMERGENCY DECLARED; AIRCRAFT LANDED OVERWEIGHT WITHOUT INCIDENT. MAINTENANCE REPLACED BOTH PTU ISOLATION COUPLING HALVES IAW AMM 29-13-15.