ERA23LA327 · Air Tractor AT502 B
Air Tractor AT502 B · Accident: loss of engine power (total) while maneuvering
From Ruhes Airport (R47) to an unrecorded destination
Event
- NTSB case
- ERA23LA327
- Event typeAccident: someone killed or seriously injured, or the aircraft substantially damaged (NTSB definition). Incident: an occurrence that affected or could have affected safety, short of that. Glossary
- Accident
- InvestigationHow far the investigation had got when the record was published: preliminary, ongoing, final or completed. Unknown where the source does not say. Glossary
- Completed
- API-reported fatalities
- 0 · all aircraft and ground
- Ground fatalities
- 0
- OperationWhat kind of flying it was, grouped by the rules it flew under: airline (US Part 121), air taxi and commuter (Part 135), general aviation (Part 91 and similar), military or government. Glossary
- General aviation
- WeatherVisual meteorological conditions (VMC): good enough to fly by looking outside. Instrument conditions (IMC): cloud or low visibility, flying by instruments. Glossary
- Visual Meteorological Cond
Air Tractor AT502 B
- Aircraft type
- Air Tractor AT502
- Category
- Airplane
- RegistrationThe aircraft's tail number, such as N12345 or G-ABCD. Registrations are reissued, so the same one years apart can be a different aircraft. Glossary
- N5048S
- Operator
- Unknown
- Onboard fatalities
- Unknown
- Route
- From Ruhes Airport (R47), Leipsic, OHTo not recorded
- Aircraft age
- About 25 years (built 1998)
- Flight rulesThe regulations the flight operated under: in the US, Part 91 (general aviation), Part 121 (airlines), Part 135 (air taxi and commuter) and others; for flights abroad, the NTSB's coarser commercial or non-commercial code. Glossary
- Part 137: Agricultural
- Phase of flightThe stage of the flight when things started to go wrong: standing, taxi, takeoff, initial climb, en route, maneuvering, approach or landing. Glossary
- Maneuvering · low-altitude flying
- Defining eventThe single coded event the NTSB judges best describes what happened (records from 2008 on). Older records name the first occurrence in the sequence instead. Glossary
- Loss of engine power (total)
- DamageDestroyed: beyond practical repair. Substantial: damage that affects the structure, performance or handling and normally needs major repair. Minor: less than that. Glossary
- Substantial
Cause areas
- Aircraft › Aircraft power plant
- Organizational issues › Support/oversight/monitoring
Approximate · Coordinates as recorded by the NTSB; no uncertainty radius is established.
NTSB narrative
During the first aerial application flight of the day, the pilot noted no engine performance anomalies. After starting the second flight over the intended field, the pilot heard a “pop” and observed flames emitting from the engine exhaust ducts; then the engine sustained a total loss of power. He performed a forced landing to a field and the airplane sustained substantial damage to the left wing. About 8½ years before the accident, the engine was overhauled and reinstalled on the airplane. The records for the engine overhaul work order were no longer available. Since the overhaul, the airplane and engine received nine annual inspections and had accumulated 563.3 hours of service. Postaccident examination of the engine revealed that the reduction gear box (RGB) second-stage ring gear was assembled incorrectly in front of the retaining plates instead of the retaining plates being fixed within the dedicated slot on the ring gear. The incorrect assembly allowed the second-stage ring gear to migrate forward into the RGB front housing. This allowed reduction in the second-stage ring gear axial meshing spline engagement, to the point where the remaining contact surface could no longer sustain the ring gear load. The small overlapping region sheared off circumferentially, allowing the ring gear to spin freely and resulting in the decoupling of the power turbine (PT) disc from the propeller shaft. The reduced support by the second-stage ring gear resulted in an increase in movement of the second-stage carrier assembly. That movement then transmitted to the RGB first-stage carrier sun gear, where damage was observed on the mating teeth; the movement also resulted in excessive loads on the No. 3 bearing outer ring that resulted in its fracture. The loss of support from the No. 3 roller bearing resulted in an imbalance of the PT disc assembly that resulted in the blades fracturing. The PT vane previously had a repair performed that was not approved by the manufacturer; however, it likely did not influence the initial engine malfunction.
Probable cause
The incorrect assembly of the turbine engine’s reduction gear box second-stage ring gear, which resulted in an internal failure of multiple engine components and a total loss of power.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record ERA23LA327
- Event ID
- 20230807192812
- Case number
- ERA23LA327
- Dataset
- full-current
- Source SHA-256
- 5cf380f0061817c0331a6b2d8cc7e0ee3a79bea469a1001dc5c10e56f35f5ab3
Source notes (4)
- Unreviewed is an editorial label, not an investigation status. API-sourced is not report-checked or human-reviewed. Explicit event totals are used without summing aircraft injury tables; onboard allocation is withheld. Unknown values remain unknown. The operation category is mapped from the NTSB-reported FAR part and has not been reviewed.
- Filled from the NTSB case API where the bulk record had no value: investigation status, cause areas. Values present in the bulk record are kept.
- The date is the local date, which is the same as the UTC date the NTSB stores.
- API snapshot SHA-256: e4f899acf351ea850a829a105ab224a7fe492ee255a7accfee43e034e84c7de7; retrieved 2026-09-16T17:58:17.997Z.