Grumman Acft Eng Cor-Schweizer G-164B N48485 accident near Bloomfield, Nebraska

Probable cause

A partial loss of engine power during takeoff for reasons that could not be determined.

NTSB analysis

The operator reported that the first flight of the day was completed without incident. However, during takeoff for the second flight of the day, the airplane started to lift off the runway but would not climb. The pilot applied full throttle, but the engine did not respond. The airplane went through a fence off the end of the runway and came to rest in a soybean field which resulted in substantial damage to the upper and lower right wings.

An engine examination did not reveal any evidence of an uncontained failure or external fire damage. The engine contained multiple indications of power at the time of impact, such as rotational scoring damage by the compressor impellers and turbine blades and earthen material present within the engine. In addition, the torsion shaft was fractured in torsional overload resulting from sudden stoppage due to impact of the propeller.

Bench testing determined that the fuel control unit (FCU) cam initially moved axially as the compressor inlet pressure (Pt2) was increased but then stopped moving. Upon disassembly of the fuel control unit, the cam gear was seized in position on the shaft. Metallurgical examination of the camshaft found two depressions on opposite corners of the camshaft slot. The outer camshaft diameter was larger than the specified diameter in the area of the two depressions. The bushing exhibited corresponding areas of wear and distinct gouges along the axis of the bushing and on either side of the shaft slot. One gear tooth on the camshaft exhibited signs of spalling damage and cracking across the entire length of the tooth.

The FCU camshaft deformation may have restricted cam translation, which would have reduced metered fuel flow. However, if the camshaft was restricted, the condition would have been present on previous flight(s) since the camshaft translation was a function of altitude changes. It is unlikely that the FCU contributed to the lack of throttle response.

A fuel sample taken from the fuel filter bowl consisted of Jet A fuel and water. However, the quantity of water was not consistent with any degradation of engine performance.

The investigation was unable to determine the reason for the reduction of engine power during the accident takeoff.

Text from the NTSB. Open the NTSB docket for CEN23LA232 for the full record.