WPR17LA174 · Rockwell International S 2R UNDESIGNAT
Rockwell International S 2R UNDESIGNAT · Accident: powerplant system/component malfunction/failure while maneuvering
From Brawley, CA to Brawley, CA
Event
- NTSB case
- WPR17LA174
- 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
- Unknown
- 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
Rockwell International S 2R UNDESIGNAT
- Aircraft type
- Rockwell S-2
- 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
- N4913X
- Operator
- Unknown
- Onboard fatalities
- Unknown
- Route
- From Brawley, CATo Brawley, CA
- Aircraft age
- About 43 years (built 1974)
- 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
- Powerplant system/component malfunction/failure
- 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
Approximate · Coordinates from the NTSB case API, which marks them as estimated or does not say; no uncertainty radius is established.
NTSB narrative
The commercial pilot reported that, while conducting low-level maneuvering over a field during the agricultural application flight, the engine lost partial power . The pilot leveled the wings, and the engine momentarily regained some power; however, shortly after, it started to lose power again. The pilot subsequently initiated an off-airport landing to a field. During the landing roll, the propeller struck the ground, and the landing gear were torn off. Both wings, the engine mounts, and the bottom of the fuselage sustained substantial damage.
Postaccident examination of the engine revealed that three of the supercharger drive gear teeth had broken, one of which was found in the engine oil sump. Examination of the gear teeth fracture surfaces revealed features and topographies consistent with bending overstress separations. Contact patterns and pitting were noted on the pressure faces of the remaining intact gear teeth, which were indicative of heavy loading. No preexisting cracks were found. The thrust bearing exhibited damage consistent with a propeller strike.
A representative from an engine overhaul facility that overhauls the accident engine make and model (but did not overhaul the accident engine) reported that it is unlikely that the gear teeth fractured during the accident sequence given that one of the separated gear teeth was found in the oil sump and not in the supercharger blower section because typically when a gear tooth separates during flight, the oil flow will carry the broken fragment down into the sump. The representative reported that the gear teeth usually break due to either a sudden engine stoppage or fatigue or stress cracking. The fatigue or stress cracking can often be the result of a propeller strike and, if left unchecked, can result in the eventual separation of the affected gear teeth. He stated that it is possible for an engine to continue operating relatively normally with only one gear tooth missing; however, multiple broken gear teeth would result in a decrease in power of the supercharger section.
Maintenance records were not made available for review during the investigation; therefore, it could not be determined if a propeller strike or sudden engine stoppage was reported before the accident.
Probable cause
The partial loss of engine power due to the overstress separation of three supercharger drive gear teeth.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record WPR17LA174
- Event ID
- 20170801X12647
- Case number
- WPR17LA174
- 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, coordinates. 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: 8d12180a8ac365202a3add919109ec214bb71b86270af414a4e1b8fcf961854c; retrieved 2026-09-16T05:38:27.107Z.