Aero Commander S2R N5553X accident near Vinton, Iowa

Probable cause

Loss of throttle control input due to a failure in the throttle control system. Contributing to the accident was the inadequate inspection and reinstallation of worn parts by maintenance personnel.

NTSB analysis

The pilot stated that on final approach, he slowed the airplane for landing. When the airplane crossed the end of the runway, he reduced the throttle back, but the airplane would not slow, so he executed a go-around. During the go-around, the engine lost partial power and would not respond to the pilot’s throttle inputs. The pilot then executed a forced landing in a cornfield, and the airplane sustained substantial damage to the fuselage and empennage.

Examination of the throttle control system revealed that the interlocking teeth mechanisms between the carburetor lever stop assembly and the throttle control lever were worn and lost integrity to interconnect. The teeth on the lever stop assembly were severely worn. Thus, it is likely that during the accident flight, when the pilot actuated the throttle control lever, the throttle control system failed when the worn-down teeth on the lever stop would not engage the teeth on the mating throttle control lever. This caused a loss of the throttle lever input, which allowed the engine to enter a low rpm condition. The material examination also noted a mismatch in hardness of the associated parts; although the hardness values were typical for the respective part compositions and microstructures, the mismatch in hardness lent itself to higher wear rates. A review of the airplane’s maintenance records revealed that the carburetor had been removed for overhaul and reinstalled 135 hours before the accident. It is likely that maintenance personnel reinstalled the worn parts without thoroughly inspecting them.

Text from the NTSB. Open the NTSB docket for CEN18LA278 for the full record.