As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
JFK INFLIGHT T1881/17MAR - CREW REPORTED LOSS OF YELLOW HYDRAULIC SYSTEM DURING CLIMB. RETURNED TO JFK AND LANDED WITHOUT INCIDENT. REPLACED NUMBER TWO ENGINE YELLOW SYSTEM HYDRAULIC PUMP AND CASE DRAIN FILTER. SYSTEM GROUND CHECKED NORMAL OPERATION.