NTSB Identification: DFW05IA048.
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Incident occurred Wednesday, December 29, 2004 in Natchitoches, LA
Probable Cause Approval Date: 06/28/2006
Aircraft: Beech A36, registration: N920GL
Injuries: 4 Uninjured.

NTSB investigators used data provided by various sources and may not have traveled in support of this investigation to prepare this aircraft incident report.

The 15,000-hour commercial pilot reported that while he was in cruise flight at 12,000 feet mean sea level (msl) during an IFR cross country flight, he began to smell smoke and noticed the engine began to surge. After requesting a lower altitude, the air traffic controller advised him of the nearest airport. During the descent, at an altitude of approximately 9,000 feet msl, "the engine lost oil pressure" and the pilot shut the engine down using the mixture control. The "engine continued to turn over" as he heard "several loud explosions and observed fireballs at the propeller hub" before the propeller stopped turning. After realizing he was unable to make it to the airport, the pilot elected to land in a field approximately 1/2 mile south of his intended airport. After maneuvering the airplane under a set of power lines, the pilot landed in an open field. A detailed examination of the engine was completed at the facilities of the engine manufacturer. The examination revealed that the crankshaft and counterweights assembly exhibited lubrication distress of a varying degree to all connecting rod journals and bearings. The number six piston head exhibited detonation and pre-ignition damage. The examination concluded that a turbo-normalizing system had been installed and the installation of a turbo-normalizing system on an engine originally certificated as a normally aspirated model containing high compression pistons is contrary to the recommendations in TCM Service Bulletin M64-18 and can reduce the engine's detonation margins.

The National Transportation Safety Board determines the probable cause(s) of this incident to be:

The loss of engine power due to pre-ignition and detonation. Contributing factors were the lack of suitable terrain available for the forced landing and the unapproved installation of a turbocharger.

Full narrative available

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