What happened
The aircraft arrived from the west and landed on the airstrip. According to the owner of the airstrip, the pilot taxied the aircraft to the west end of the runway before performing a takeoff toward the east. The witness described the initial takeoff as perfect and noted that the engine sounded normal during the departure.
After the aircraft was no longer visible, the witness heard two sounds resembling shots. The witness's wife later reported seeing the aircraft enter a left banking turn, followed by two puffs of smoke and two loud bangs before the aircraft disappeared from view. While the witness expected the pilot to return to the airstable, the aircraft did not return. Approximately 30 minutes later, the witness was informed by a friend that the aircraft had gone down.
The investigation
An examination of the aircraft revealed no mechanical anomalies. However, investigators noted that all engine spark plugs were light brown in color, which is indicative of the engine being operated at a lean fuel-air mixture setting.
A manufacturer's representative stated that when using the installed turbocharger, the operator must maintain a rich mixture setting to achieve the same performance at high elevations as seen at sea level. Any leaning of the mixture could produce backfires and a loss of engine performance. At the time of the event, the calculated density altitude for the area was 11,246 feet MSL. Data regarding the turbocharger indicated that at 13,000 feet MSL and 76 percent horsepower, the aircraft's climb rate was 500 feet per minute.