Beech E35 N3315C accident near Okeechobee, Florida

Probable cause

The separation of the throttle control cable from the carburetor throttle control lever resulting in the near total loss of engine power. Contributing to the separation of the throttle cable was the lack of proper securing hardware by unknown maintenance personnel.

NTSB analysis

While climbing on course shortly after takeoff on a cross-country flight, the engine briefly ran roughly before losing partial power. The private pilot maneuvered the airplane and executed an off airport forced landing with the landing gear retracted. A postimpact fire on the right side of the airplane ensued after it came to rest, and the airplane was destroyed.

Examination of the engine following accident revealed the throttle control cable was separated from the intact carburetor throttle control lever. Examination of a bolt with an attached washer, a separate washer, and a castellated nut found in the engine compartment revealed the nut was not self-locking and the tare torque was no greater than 0.2 pound-force-inch. There were no remains of a cotter pin in the recovered drilled bolt. Although the mixture control cable remained attached to the intact mixture control lever, a castellated nut and cotter pin were not attached to the bolt. Further examination of the engine and its systems otherwise revealed no evidence of preimpact mechanical failure or malfunction; Given this evidence, it is likely that the loss of engine power was due to the separation of the throttle control cable from the carburetor, which rendered sustained flight impossible.

A review of the maintenance records indicated that more than 13 months before the accident, the pressure carburetor was overhauled then reinstalled. It was the subject of two scheduled inspections before the accident. The maintenance records did not document any subsequent work to the throttle or mixture control cables. The mechanic indicated that he was certain that the proper hardware to secure the throttle cable to the throttle control lever was installed at carburetor installation and during both subsequent scheduled inspections. Although the nut lacked any appreciable tare torque, it could not be determined when it separated or if the mechanic failed to install a cotter pin to secure the throttle cable to the throttle control lever more than 13 months and a minimum of 192 flight hours earlier. Although possible, it is unlikely that the mechanic would have twice overlooked the lack of proper securing hardware during the subsequent scheduled inspections.

Text from the NTSB. Open the NTSB docket for ERA20LA044 for the full record.