Accident Overview
On an unspecified date in 1999, a Cessna T206H, operated as a public aircraft, suffered a loss of engine power while in cruise flight at approximately 1,150 feet above ground level. Spectrum analysis of air traffic control transmissions indicated a propeller speed of 1,669 revolutions per minute following the power loss. Visual meteorological conditions prevailed, with recorded surface winds from the northeast.
Witness Observations
Witnesses reported hearing several attempted engine restarts as the pilot maneuvered the airplane for a forced landing on a 500-foot-long fallow agricultural field north of a house. During each start attempt, black smoke was observed emanating from the airplane. The Airframe & Powerplant Mechanics Handbook states that black smoke indicates a mixture that is "too rich."
Impact and Fire
During the forced landing, the airplane's wing and horizontal stabilizer contacted trees near the house, resulting in a steep descent into the adjacent garage. A post-crash fire and explosion ensued.
Examination of the Airplane
Post-accident examination of the airplane's systems and components revealed that the turbocharger could not be rotated, and a hydraulic press was required to remove the turbocharger turbine wheel. The engine crankcase halves exhibited fretting, and the nut of one crankcase thru-bolt was not in place. Maintenance records indicated that the crankshaft had been replaced in response to airworthiness directives and service bulletins. No other anomalies that would have precluded normal operation were found.
Emergency Procedures and Recommendations
In 1994, the National Transportation Safety Board issued recommendation A-94-081, relating to emergency procedures for turbocharger failures to be included in airplane pilot operating handbooks (POHs) and airplane flight manuals. The Cessna T206H POH does not list emergency procedures for turbocharger failures. Under emergency procedures, the POH advises advancing the mixture control to the rich position if restart does not occur. The manufacturer's airplane pilot safety supplement, reissued in 1998 to incorporate turbocharger failures, states that "If a turbocharger failure results in a loss of power, it may be further complicated by an overly rich mixture."
Emergency Egress Considerations
A review of emergency exit procedures for Cessna 206 models indicates that with flaps lowered, the forward portion of the cargo door can only be opened approximately 4 inches to allow the aft portion of the cargo door to be opened during emergency egress. The distance between the cabin roof and seat back was measured to be approximately 11 inches.