N48485Grumman Acft Eng Cor-Schweizer G-164B · 1976

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 (CFR) 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 it 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.

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. A fuel sample taken from the fuel filter bowl consisted of Jet A fuel and water.

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.

Bench testing determined that the cam moved axially as the compressor inlet pressure (Pt2) was increased. However, at 11 psia, the cam did not move any further. On 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. Additionally, the outer camshaft diameter was larger than the specified diameter near 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 propeller governor assembly was intact and undamaged, the input driveshaft

rotated freely under hand pressure and the control arm rotated normally. Bench testing of the propeller governor resulted in normal operation.

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 hours or 5,400 hours depending on the operator’s chosen engine management program. However, compliance with the engine manufacturer’s 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 for agricultural aircraft.