What happened
The flight originated at Mammoth Lakes, California, with a destination of Palo Alto. While en route at 18,000 feet over the Sierra Nevada Mountains, the pilot noted erratic high oil temperature and low oil pressure readings. The pilot diverted to Modesto to seek maintenance; however, because no mechanics were available, the pilot continued toward Palo Alto after adding oil to the engine.
During the flight in actual IFR conditions, the pilot experienced erratic operation of both GPS navigation systems. Shortly thereafter, the oil pressure and temperature indications became unstable again, with temperatures near the upper limit and pressures near the lower limit. The pilot attempted to reset the system by cycling circuit breakers, but the audible alarms for oil temperature and pressure sounded. Additionally, the ice warning system activated, and the pilot observed clear ice breaking off the wings after activating deice functions. Fuel gauge indications also became erratic.
The pilot requested an immediate landing. Although a nearby airport with an 11,000-foot runway was suggested, the pilot elected to continue to Palo Alto, which was only eight minutes away. To avoid the risk of engine failure over a populated area, the pilot requested a straight-in approach on runway 31. The pilot noted being high on the approach but did not execute a go-around due to concerns regarding potential engine failure. The aircraft landed halfway down the 2,500-foot runway and could not stop, resulting in 0 fatalities as the plane overran the runway and struck a berm and marshy terrain approximately 300 yards beyond the end of the runway.
The investigation
The investigation included a review of the integrated engine parameter instrument and warning system (EMIS). When placed into exceedance review mode, the Enhanced Digital Indicator (EDI) showed recorded exceedances for oil temperature, oil pressure, manifold pressure, and turbine inlet temperature.
A functional test of the EMIS system, including all probes, analog gauges, and associated wiring, was performed with no anomalies found. Investigators also attempted to replicate the fluctuating oil temperature by manipulating the electrical connection of the temperature probe, but they were unable to duplicate the fluctuations. A detailed examination of the engine revealed no evidence of a malfunction within the lubrication system or any lubrication-related damage to the core engine.