Flight History
The flight originated from Mammoth Lakes, California, with a destination of Palo Alto. While en route at 18,000 feet over the Sierra Nevada Mountains, the pilot observed erratic high oil temperature and low oil pressure readings and diverted to Modesto for an engine check. No mechanics were available at the airport. The pilot added oil to the engine and departed for the remaining 65-mile trip to Palo Alto, heading west.
System Anomalies
En route to Palo Alto in actual IFR conditions, the pilot experienced erratic operation of both GPS navigation systems; one failed after losing satellite lock. The pilot noted that this was troubling due to a prior bad experience with navigation system loss in IFR and icing conditions in a non-radar environment. Shortly after, oil pressure and oil temperature indications became erratic, with the temperature flickering near the upper limit and pressure near the lower limit. The pilot reported pushing reset buttons and cycling circuit breakers; the audible alarms for oil temperature and pressure sounded. The ice warning system activated, alerting the pilot to select deice functions. After activating deice, the pilot observed clear ice breaking off the wings. Fuel gauges then gave erratic indications, cycling to near empty and back.
Approach and Landing
The pilot told the TRACON controller she needed to land as soon as possible. The controller suggested two nearby airports, one with an 11,000-foot runway, but the pilot elected to continue to Palo Alto as the original destination was only 8 minutes further. As she approached the airport, oil temperature continued to fluctuate and the warning horn sounded; she repeatedly reset it. The pilot was given winds at Palo Alto (120 degrees at 8 knots) and, concerned about losing the engine over a populated area, requested runway 31 for a straight-in approach. She was cleared to land on the 2,500-foot runway 31. The pilot stated she realized she was high on the approach but did not consider a go-around due to concern about potential engine failure. The airplane landed about halfway down the runway and could not stop before overrunning the runway and colliding with a berm and marshy terrain about 300 yards beyond the runway end.
Post-Accident Examination
The aircraft was equipped with an integrated engine parameter instrument and warning system (EMIS). The Enhanced Digital Indicator (EDI) was placed into exceedance review mode and reported: three oil temperature exceedances (peak 278, average 278 for 11 seconds); one oil pressure exceedance (peak 0, average 0 for 81 seconds); nine manifold pressure exceedances (peak 42.0, average 42.0 for 2 seconds); one turbine inlet temperature exceedance (43 seconds, average 1750). Cylinder head temperature, fuel flow, and propeller rpm showed no exceedances. A functional test of the EMIS system, including probes, analog gauges, and wiring, found no anomalies. Forcible manipulation of the temperature probe electrical connection failed to duplicate a fluctuating indication. A detailed engine examination found no evidence of lubricating system malfunction or lubrication-related damage to the core engine.