Accident Details
On June 7, 2023, about 1400 central daylight time, a Grumman G-164B airplane, N48485, was substantially damaged when it was involved in an accident near Bloomfield, Nebraska. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 137 aerial application flight.
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.
Aircraft Damage
The upper and lower right wings were damaged during the impact sequence. The engine remained secured to the engine mount. The propeller assembly remained attached to the reduction gearbox. Each propeller blade was deformed, and the outboard portion of one blade was separated consistent with the impact sequence. Continuity of the engine controls was confirmed.
Engine and Fuel Analysis
An engine examination did not reveal any evidence of an uncontained failure or external fire damage. The compressor impellers and turbine rotors/blades were intact. Earthen material was observed from the stage 1 compressor impeller through to the combustion chamber. The stage 2 compressor impeller was intact and exhibited localized rotational scoring damage. Stage 1 turbine rotor blade tips exhibited rotational scoring, and the torsion shaft was fractured. Metallurgical examination determined that the torsion shaft fractured due to torsional overload.
A fuel sample taken from the fuel filter bowl consisted of Jet A fuel and water.
Bench testing determined that the fuel control unit cam moved axially as compressor inlet pressure increased, but at 11 psia, the cam did not move further. On disassembly, 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. Additionally, the outer camshaft diameter was larger than the specified diameter near the depressions. The bushing exhibited corresponding wear and distinct gouges. One gear tooth on the camshaft showed spalling damage and cracking across the entire tooth length.
The propeller governor assembly was intact and undamaged, the input driveshaft rotated freely, and the control arm rotated normally. Bench testing resulted in normal operation.
Maintenance Records
Airplane maintenance records noted that the engine was overhauled in September 1987. The engine logbook did not contain a record of any subsequent engine overhaul. Based on the records, the engine had accumulated about 8,428 hours since overhaul. The engine manufacturer’s time between overhaul (TBO) was either 3,600 or 5,400 hours depending on the operator’s engine management program. Compliance with TBO requirements is not mandated by the Federal Aviation Administration for 14 CFR Part 137 operations.
At the time of the accident, the operator reported the airplane weight at 6,830 lbs. The weight and balance data noted an airplane gross weight of 5,500 lbs. However, regulations may permit agricultural operators to establish a maximum weight as an operating limitation.