1996-04-02: While in cruise flight, the pilot of a Piper PA31
Navajo noticed a drop in the right engine oil pressure. The pilot shut the engine down and returned to St. Andrews Airport. ERS were called out and aircraft landed without further incident. There was no damage to the aircraft or injury to the 9 SOB. The loss of oil pressure was traced to an oil leak past the piston cup-seal in the turbo charger waste gate valve. The waste gate valve had been newly overhauled and installed on the aircraft. The waste gate valve was returned to the overhaul agency for their evaluation. The company will be submitting and SDR to Transport Canada. The overhaul agency discovered that during overhaul a portion of the rubber lip of the cup-seal had been curled under during installation allowing engine oil to leak past the seal. The overhaul agency will take extra caution when complying with Lycoming Service instruction (SI) 1416 regarding the installation of a new cup seal. They have also amended the test procedure to provide for a higher test pressure when testing newly overhauled waste gate valves. The higher test pressure should identify any cup seals that are inadvertently rolled under.