As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON CLIMB OUT, NR 1 ENGINE BEGAN TO LOSE OIL PRESSURE. CREW ELECTED TO SHUT DOWN THE ENGINE AND LAND. MX FOUND THE OIL SERVICING CAP NOT INSTALLED. THE CAP WAS FOUND NEAR THE ACCESSORY GEARBOX AND THE CAP'S O-RING APPEARED TO BE EXPANDED. MX REPLACED THE O-RING AND REINSTALLED THE CAP.