Accident Overview
On July 22, 2023, at approximately 1113 central daylight time, a Grumman G-164A, registration N9892, experienced a loss of engine power during an agricultural application flight. The aircraft was substantially damaged following a forced landing in a corn field near Patoka, Illinois. The pilot reported no injuries.
Flight and Landing
The pilot was conducting the fourth pass of a chemical spray load when the engine lost power. Due to the low altitude and decreasing airspeed, the pilot executed a forced landing into the corn field. Post-accident examination confirmed flight control continuity. The airplane was retained for further examination.
Engine Examination
The turboprop engine was examined at the manufacturer's facility. The examination revealed rotational scoring, hard body impact damage, and missing material throughout the compressor turbine (CT) and power turbine (PT) sections. Multiple CT blades were fractured above the blade platform, and approximately 75% of the PT blades were fractured at various lengths above the blade platform. Metallurgical analysis of two CT blades showed material necking near fracture surfaces, microstructural rafting, creep voids, and localized microstructure alteration consistent with heat-related material degradation.
Fuel Control Unit Findings
Examination of the fuel control unit (FCU) found that the maximum Ng speed adjustment screw had been adjusted to the maximum fuel flow position and was lock wired in place. Additionally, the FCU housing was missing a bolt and exhibited a fatigue fracture that created a gap between the FCU housings. Movement of the power control linkage caused a reactive opening and closing of this gap.
Maintenance Records
The operator reported the engine's time since new (TSN) as 14,092 hours. The time since overhaul (TSO) was 6,738.5 hours, and the time since inspection was 226 hours. A review of engine logbooks showed that the aircraft had undergone an annual inspection approximately two months before the accident. The recorded TSN at that annual inspection was 14,217 hours. A corresponding airplane logbook entry showed the airplane TSN as 12,475 hours. The engine manufacturer's recommended time between overhauls (TBO) is 3,600 hours.
Damage Summary
The substantial damage included both wings, the fuselage, and the empennage.