CEN23LA231

The pilot reported that shortly after takeoff on the fourth flight of the day, he leveled the airplane about 500 ft above ground level (agl), and set the engine controls for 2,500 rpm and 25 inHg manifold pressure. Immediately after adjusting the engine controls, the engine speed decreased to idle. The pilot made a forced landing to a field and the airplane sustained substantial damage to the left wing. A postaccident examination revealed that the throttle control lever had fractured, and the throttle control was no longer connected. The associated hardware remained attached to the throttle control cable attachment end. The engine and fuel control valve were recently overhauled, reinstalled in the airplane, and had accumulated 86.3 hours. A postaccident metallurgical examination revealed the throttle control lever attachment point exhibited wear and deformation on the surfaces of the areas that would have been in contact with the rod end attachment hardware. The throttle control lever attachment point also exhibited wear and a shallow impression of the splined collar on the inner surface of the attachment point bore, which was significantly worn. The splines on the collar were worn and uneven. The wear and deformation to the throttle control lever attachment point and the wear in the attachment point’s bore resulted in dimensions that no longer provided enough interference with the rod end attachment hardware to secure the connection. The throttle linkage hardware build-up on the accident airplane was different than specified by the airplane service manual and was missing a washer. The difference likely resulted in the hardware becoming loose over time and allowing excessive wear of the splined collar and lever arm, and ultimately the failure of the lever arm attachment point.

On June 6, 2023, about 1208 central daylight time, a Cessna 207 airplane, N91157, was substantially damaged when it was involved in an accident near Valley International Airport (HRL), Harlingen, Texas. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 aerial application flight. The pilot stated that the purpose of the flight was to distribute sterile fruit flies in the area, and he had already completed three similar flights that morning. After the third flight, the fuel tanks were topped off and additional fruit flies were loaded into the airplane. The pilot departed, proceeded southeast about 500 ft agl, and set the engine controls for 2,500 rpm and 25 inHg manifold pressure. Immediately after adjusting the engine controls, the engine speed decreased to idle. He was unable to fly back to the airport, so he made a forced landing in a field. During the forced landing, the airplane sustained substantial damage to the left-wing spar. A postaccident examination revealed that the throttle control lever had fractured, and the throttle control was no longer connected. The associated hardware remained attached to the rod end. The engine and fuel control valve were overhauled and reinstalled on the airplane April 14, 2023. The engine had accumulated 86.3 hours since overhaul. The fractured throttle control lever and associated hardware were examined by the National Transportation Safety Board Materials Laboratory. The throttle control lever attachment point exhibited plastic deformation on the surfaces of the areas that would have been in contact with the rod end attachment hardware. This deformation resulted in a variable thickness across the attachment point. The throttle control lever attachment point also exhibited wear and a shallow impression of the splined collar on the inner surface of the attachment point bore, which was significantly worn. The splines on the collar were worn and uneven. The plastic deformation to the throttle control lever attachment point and the wear in the attachment point’s bore resulted in dimensions that no longer provided enough interference with the rod end attachment hardware to secure the connection. On January 26, 1996, the airplane manufacturer issued Service Bulletin SEB 95-15 Rev 1, Engine Throttle Control Lever Inspection. The SEB was issued due to wearing at the throttle control cable attachment end, where in some cases the wear progressed through the lever allowing the throttle control end to become disconnected from the lever. The SEB warned that failure to complete the inspection could result in the loss of engine throttle control and an incontrollable reduction in engine power to idle rpm in flight. The SEB and the airplane service manual provided a diagram of the proper throttle linkage hardware build up. The throttle linkage hardware build-up on the accident airplane was different than the service manual and was missing a washer.