Accident Details
On June 6, 2023, at approximately 1208 central daylight time, a Cessna 207 airplane, registered as N91157, sustained substantial damage during a forced landing near Valley International Airport (HRL) in Harlingen, Texas. The pilot was not injured. The flight was conducted under Title 14 Code of Federal Regulations Part 91 as an aerial application operation.
Pilot Account
According to the pilot, the purpose of the flight was to distribute sterile fruit flies in the area. He had already completed three similar flights earlier that morning. After the third flight, the fuel tanks were topped off and additional fruit flies were loaded. The pilot departed and climbed to about 500 ft above ground level (AGL). He then set the engine controls to 2,500 rpm and 25 inHg manifold pressure. Immediately after adjusting the controls, the engine speed decreased to idle. Unable to return to the airport, the pilot executed a forced landing in a field. During the landing, the left-wing spar sustained substantial damage.
Postaccident Examination
A postaccident examination revealed that the throttle control lever had fractured, resulting in a disconnection of the throttle control. The associated hardware remained attached to the rod end. The fractured lever and hardware were examined by the National Transportation Safety Board Materials Laboratory. The examination showed plastic deformation on the surfaces of the attachment point that would have been in contact with the rod end hardware. This deformation caused a variable thickness across the attachment point. Additionally, the inner surface of the attachment point bore exhibited wear and a shallow impression from the splined collar, which was significantly worn. The splines on the collar were also worn and uneven. The plastic deformation and wear resulted in dimensions that no longer provided sufficient interference to secure the connection.
Maintenance History
The engine and fuel control valve had been overhauled and reinstalled on the airplane on April 14, 2023. At the time of the accident, the engine had accumulated 86.3 hours since the overhaul.
Service Bulletin Information
On January 26, 1996, the airplane manufacturer issued Service Bulletin SEB 95-15 Rev 1, titled "Engine Throttle Control Lever Inspection." The bulletin was prompted by reports of wear at the throttle control cable attachment end, which in some cases progressed through the lever, allowing the throttle control end to become disconnected. The SEB warned that failure to perform the inspection could lead to loss of engine throttle control and an uncontrollable reduction in engine power to idle rpm in flight.
Hardware Build-up Discrepancy
Examination of the accident airplane's throttle linkage revealed that the hardware build-up differed from the diagram provided in the SEB and the airplane service manual. Specifically, a washer was missing from the assembly.