As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER 4 MINUTES OF FLIGHT, LEFT ENGINE TORQUE WENT TO ZERO AND LOST OIL PRESSURE. AIRCRAFT RETURNED TO FIELD ON RIGHT ENGINE ONLY WITHOUT FURTHER INCIDENT. MAINTENANCE REMOVED AND REPLACED THE LH HYDRO MECHANICAL UNIT, GROUND RUNS CHECKED GOOD AND AIRCRAFT WAS RETURNED TO SERVICE.