Incident Overview
On March 1, 2015, at 0940 Pacific standard time, a Piper PA-46-310P, registration N9133G, executed a forced landing into Roberts Field Airport in Redmond, Oregon. The airplane was operated by a private pilot under 14 CFR Part 91. The pilot was not injured. The airplane sustained substantial damage to both wings. Visual meteorological conditions prevailed, and an instrument flight plan had been filed. The flight originated from Oak Harbor, Washington, at 0800.
Pilot Report
The pilot reported cruising at 23,000 feet mean sea level (msl) when he noticed the engine running rough as he passed Portland, Oregon. He observed that the number 5 cylinder head temperature (CHT) was lower than normal. He cycled the magnetos and found that the engine ran rougher when the left magneto was selected. Enriching the mixture smoothed the engine. He continued monitoring and adjusting the mixture. About 30 minutes later, engine power dropped completely. The pilot diverted to Roberts Field using GPS. Approximately 2 miles from the airport, he sighted the field but lacked altitude to align with a runway. He performed a forced landing into the airport infield, resulting in a collapsed nose landing gear and wing spar damage at both main landing gear mounts.
Post-Accident Examination
On March 3, 2015, an airframe and power plants (A&P) mechanic examined the airplane under Federal Aviation Administration (FAA) supervision. He documented the airframe structural damage but found no obvious reason for the loss of engine power. The airplane was then moved to a facility in Greeley, Colorado, for further examination.
Engine Data Analysis
The airplane was equipped with an EDM 930 engine data monitoring system. On April 14, data from the EDM 930 was downloaded and sent to the National Transportation Safety Board (NTSB) Investigator-in-Charge (IIC). The data showed that about 25 minutes before the power loss, the number 5 cylinder head temperature began trending about 50°F below its previous steady 300°F, then fluctuated twice between 300°F and 250°F during the final 12 minutes. The exhaust gas temperature (EGT) for cylinder 5 remained steady throughout. All other cylinders displayed steady EGT and CHT values.
Engine Test and Findings
On May 13, 2015, the NTSB IIC and a technical representative from the engine manufacturer examined the airplane. A fuel sample from the fuel strainer was light green, tested negative for water or kerosene/jet fuel contamination, and chemical analysis confirmed it was consistent with 100LL avgas. The engine was examined externally: cylinders were borescoped, spark plugs inspected, internal magneto timing verified, and internal continuity confirmed by rotating the propeller/crankshaft. The number 5 cylinder fuel injection nozzle was removed, examined, and found in good condition with no blockages. An external fuel tank was plumbed into the right-wing fuel outlet with an external priming pump inline. The engine started on the first attempt, ran smoothly at idle, passed a magneto check, and was run up to red line producing full power. No anomalies were noted except that the number 5 cylinder head temperature was 50°-70°F cooler than all other cylinders.