NTSB Factual Report

On June 15, 2005, at 0900 eastern daylight time, an amateur-built Thomas Zenith CH701, N613DT, sustained substantial damage during a forced landing to a golf course near Redford, Michigan, after a loss of engine thrust. The private pilot was not injured. The Title 14 Code of Federal Regulations Part 91 personal flight departed Harsens Island (Z92), Michigan, at 0800 and was en route to Defiance, Ohio. Visual meteorological conditions prevailed at the time of the accident. No flight plan was filed.

The pilot reported that he had purchased the airplane on the morning of the accident. The airplane was issued a Special Airworthiness Certificate on July 22, 2004. The first 40 hours of operation was signed off on October 11, 2004. The last conditional inspection was conducted on March 24, 2005. The airplane had a total time of 58.2 hours at the last inspection.

The pilot reported that he departed Z92 and climbed to 2,000 feet mean sea level and obtained flight following from the Detroit Approach Control. He reported that he had flown for about one hour when he heard and felt a loud "bang" from the front of the airplane. The engine quit. He reported he immediately declared a "MAYDAY" to approach control. He executed a forced landing to a golf course. During landing rollout he encountered rough terrain, and the airplane sustained substantial damage to the engine firewall. The pilot reported that all three wooden propeller blades had separated from the propeller hub.

A Federal Aviation Administration airworthiness inspector examined the airplane. The inspector reported that the engine exhibited continuity and thumb compression. The two carburetors were found separated from their respective rubber couplers. Two of three propeller blades were recovered. The propeller hub and the two propeller blades were sent to the National Transportation Safety Board's Materials Laboratory for inspection.

The NTSB Material's Laboratory reported that the fracture surfaces of the wood on the root ends of the number 2 and number 3 propeller blades were uniform with a small amount of splintering. Small discontinuities in the fracture surface also occurred in the transitions between layers of wood. The wood of the root ends was not discolored and did not show any evidence of excess moisture or rot. Both blades appeared to be in good condition, with only a few small, shallow dents on the surface and no splintering or other damage to the blade tip or leading edge. The mating wooden fracture surface, inside the plastic insert, showed a similarly small incidence of splintering. The fracture of the wood of the three propeller blade root ends appeared to have fractured in shear stress.

Calculations indicted that normal operation of the engine would produce a shear stress of 741 psi on the propeller blades. In the manufacturer's product testing, the blade retention had not failed until the application of about 2,200 psi.

The number 1 propeller blade was not recovered which precluded its inspection for failure or defects.

NTSB Probable Cause

The total loss of engine thrust was the result of the propeller blades overstress separation from the propeller hub for an undetermined reason. An additional cause was the unsuitable terrain encountered during the forced landing.