# NTSB CEN23LA317: Grumman G-164A, N9892, Patoka, IL, July 22, 2023

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Class 3 · Limited · Final report
- Date: July 22, 2023, 11:13 local (16:13 UTC)
- Place: Patoka, IL · field
- Coordinates: 38.407, -87.5856 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=38.4070&lon=-87.5856&mi=10
- Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping)
- Defining event: [Maneuvering-low-alt flying: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342)
- Highest injury: No injuries
- Injuries: 1 uninjured
- Status: Completed
- Report: Approved by Office Director
- Investigation class: Class 3
- NTSB office: Central Region
- Parties: FAA, Transportation Safety Board of Canada
- NTSB case key (mKey): 192693
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CEN23LA317
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/192693/pdf
- NTSB docket: https://data.ntsb.gov/Docket?ProjectID=192693
- Page: https://openairdocs.org/ntsb/CEN23LA317

## Probable cause

A partial loss of engine power due to the failure of two compressor turbine blades as a result of the engine operating near or above the engine’s operating limits for an undetermined amount of time beyond the recommended engine’s TBO limit, which led to material creep and overload failure.

## Findings

NTSB's coded findings; those marked are part of the probable cause.

- [Engine (turbine/turboprop): compressor section](https://openairdocs.org/ntsb-findings/01057230): Aircraft › Aircraft power plant · Failure (probable cause); cases with it: [Grumman G-164A, 1 case](https://openairdocs.org/ntsb-findings/01057230/cases.md?model=3952704), [All aircraft, 53 cases](https://openairdocs.org/ntsb-findings/01057230/cases.md)
- [Engine (turbine/turboprop)](https://openairdocs.org/ntsb-findings/01057200): Aircraft › Aircraft power plant · Incorrect use/operation (probable cause); cases with it: [Grumman G-164A, 1 case](https://openairdocs.org/ntsb-findings/01057200/cases.md?model=3952704), [All aircraft, 67 cases](https://openairdocs.org/ntsb-findings/01057200/cases.md)

## Sequence of events

The events NTSB coded, in order, by phase of flight. The defining event best describes what happened.

- [Maneuvering-low-alt flying: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342) (defining event); cases with it: [Grumman G-164A, 7 cases](https://openairdocs.org/ntsb-events/342/sequence.md?model=3952704), [All aircraft, 1,858 cases](https://openairdocs.org/ntsb-events/342/sequence.md)

## Analysis

While conducting an aerial application flight, the pilot observed a loss of engine power. Because the airplane was at a low altitude and its airspeed was decreasing, the pilot performed a forced landing in a corn field, which resulted in the airplane sustaining substantial damage to both wings, the fuselage, and empennage. An examination of the airplane’s turboprop engine showed rotational scoring, hard body impact damage, and missing material throughout the compressor turbine (CT) and power turbine (PT) sections of the engine, indicating that the engine was producing some level of power at the time of impact. Multiple CT blades were fractured above the blade platform and about 75% of the PT blades were fractured at various lengths above the blade platform. Metallurgical examination of two of the fractured CT blades showed material necking near the fracture surfaces, microstructural rafting, creep voids, and localized alteration of the microstructure that is consistent with heat-related material degradation. Examination of the fuel control unit showed the maximum Ng speed adjustment screw was adjusted to the maximum fuel flow position and lock-wired in place. Based on the condition of the blades, the loss of engine power was likely due to the failure of two CT blades as a result of the engine being operated near or above the engine’s operating limits for an undetermined amount of time beyond the recommended engine’s time between overhaul (TBO) limit; this led to material creep and the overload failure of the CT blades.

## Factual narrative

On July 22, 2023, about 1113 central daylight time, a Grumman G-164A, N9892, was substantially damaged when it was involved in an accident near Patoka, Illinois. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 137 agricultural flight. The pilot reported that during the 4th pass of the chemical spray load, the the engine lost power. Based on the airplane’s low altitude and decreasing airspeed, the pilot elected to make a forced landing into the corn field. Both wings, the fuselage, and the empennage sustained substantial damage. Flight control continuity was confirmed. The airplane was retained for further examination. The airplane’s turboprop engine was examined at the manufacturer’s facility. The examination showed rotational scoring, hard body impact damage, and missing material throughout the CT and PT sections of the engine. Multiple CT blades were fractured above the blade platform and about 75% of the PT blades were fractured at various lengths above the blade platform. Metallurgical examination of two blades from the CT showed material necking near the fracture surfaces, microstructural rafting, creep voids, and localized alteration of the microstructure consistent with heat related material degradation. Examination of the fuel control unit (FCU) showed the maximum Ng speed adjustment screw was found adjusted to the maximum fuel flow position and was lock wired in place. Additionally, the FCU housing was missing a bolt and showed a fatigue fracture which created a gap between the FCU housings. Movement of the power control linkage was observed to cause a reactive open and close movement of the gap between the two housings. The operator reported the engine’s time since new (TSN) was 14,092 hours. The time since overhaul (TBO was 6,738.5 hours and the time since inspection was 226 hours. A review of the engine logbooks showed the airplane underwent an annual inspection about two months before the accident. The recorded (TSN) at the annual was 14,217 hours. A corresponding airplane logbook entry showed the airplane TSN as 12,475 hours. The engine manufacturer’s recommended TBO is 3,600 hours.

## Aircraft

- Registration: [N9892](https://openairdocs.org/aircraft/N9892), registered now, S/N 1324, built 1974 (OpenAirDocs)
- Reported make and model: GRUMMAN G-164A
- Registry model: [Grumman G-164A](https://openairdocs.org/model/grumman-g-164a) (registry code 3952704) (OpenAirDocs)
- Registry engine: [Pratt & Whitney PT6A series](https://openairdocs.org/engine/pratt-whitney-pt6a-series) (registry code 52034, reciprocating) (OpenAirDocs)
- Category: Airplane
- Serial number: 1324
- Year built: 1974
- Airframe hours: 14217
- Engines: Pratt and Whitney Canada PT6-20A 550 horsepower turbo prop
- Damage: Substantial damage
- Flight: Aerial application, Part 137
- Operator: Redditt Air Service Inc
- Registered owner: Redditt Air Service Inc
- Airworthiness certificate: Special, Restricted (Special)
- Last inspection: Annual, May 9, 2023
- Departed: SLO, Salem, IL
- Destination: SLO, Salem, IL
- Equipment: Stall warning system

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 32; injuries: none; commercial; airplane ratings: single-engine land; medical: class 2, without waivers/limitations; last flight review March 13, 2023; seat: center; flight hours: 16,442 total, 16,261 in this make and model, 1,591 as pilot in command

## Weather

- Conditions: Visual (VMC), Day
- Wind: 360° at 3 knots
- Visibility: 10 statute miles
- Temperature: 79 °F, dew point 64 °F
- Altimeter: 29.97 inHg
- Observed at: KAJG, 14 nm away
- METAR: KAJG 221615Z AUTO 36003KT 10SM SCT080 26/18 A2997 RMK AO2 T02640181

## FAA reports on this event (1)

The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs).

- [Accident 20230722008889A](https://openairdocs.org/incident/20230722008889A), Jul 22, 2023: Grumman G-164A, Potoka, IL, Destroyed. The aircraft accident location is 1.75 miles southeast of Potoka, IL. Lat. 38.43.58 n long. 89.04.26 w. pilot reported that he fueled at salem lockrone airport…

## Other investigations on N9892 (1)

From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model.

- [NTSB CHI08CA217](https://openairdocs.org/ntsb/CHI08CA217), Jul 28, 2008: Grumman G-164A (N9892), Veedersburg, IN, substantial damage. Probable cause: The oil filler cap not reinstalled by the pilot prior to the aerial application flight and the total loss of engine oil during an aerial application. Additional causes were the low altitude of the…

## Docket (5 files)

The files NTSB released with the investigation on July 8, 2025, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=192693. 12.1 MB in all.

- Pilot/operator aircraft accident report, NTSB form 6120.1 (item 1, PDF, 7 pages, 2.6 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16430034&FileExtension=pdf&FileName=6120_Redacted-Rel.pdf
- Photos of airplane (item 2, PDF, 4 pages, 1.8 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16430319&FileExtension=pdf&FileName=Photos%20of%20Airplane-Rel.pdf
- N9892 engine logbook (item 3, PDF, 3 pages, 2.8 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=17497720&FileExtension=pdf&FileName=N9892%20Engine%20Logbook_Redacted-Rel.pdf
- CEN23LA317_powerplant factual_final (item 4, PDF, 46 pages, 4.7 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=18610406&FileExtension=pdf&FileName=CEN23LA317_Powerplant%20Factual_FINAL-Rel.pdf
- Release of aircraft wreckage, NTSB form, airframe (item 5, PDF, 1 page, 171 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=18614456&FileExtension=pdf&FileName=Wreckage%20Release%20N9892_Redacted-Rel.pdf

From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model.

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