Flight History
The pilot reported flying the downwind leg for runway 07 when the engine oil pressure caution light illuminated. Shortly after, the engine lost power. The pilot declared an emergency and initiated a landing on runway 13. The aircraft touched down approximately two-thirds down the runway, overran the end, and struck a ditch.
Maintenance History
Eight hours before the accident flight, the owner/operator had attempted to diagnose a low oil quantity and oil venting from the crankcase breather. An airframe and powerplant (A&P) mechanic examined the engine and found no oil leaks. A cylinder compression check was performed per Teledyne Continental Motors' (TCM) Service Bulletin M89-9, "Excessive Crankcase Pressures," and no discrepancies were noted.
Engine Examination
The engine, a Teledyne Continental IO-360-ES (serial number 1393), was disassembled and examined. According to TCM's report, the connecting rod assemblies exhibited thermal discoloration. The connecting rod bearings showed lubrication distress and thermal smearing of the surface babbit, exposing the copper layer. The number four piston head had preignition/detonation damage, with thermal damage penetrating through the interior of the piston. Portions of the piston rings were missing due to thermal damage. The piston pin was intact, but the pin plug was damaged from extreme thermal exposure.
The magnetos were functionally checked and tested satisfactorily. The 12 spark plugs were also tested; core nose cracks were found on five of the 12 plugs, which were attributed to detonation but not considered detrimental to normal engine operation.
TCM's Service Bulletin M89-9 requires only a differential pressure test of the cylinders to check for cylinder preignition/detonation and excessive blow-by. It does not include the procedures outlined in TCM's SB03-3, "Differential Pressure Test and Borescope Inspection Procedures for Cylinders."
Probable Cause
No probable cause was stated in the source.