WPR16LA134 · Bell OH 58A
Farm Aviation Bell OH 58A · Accident: loss of engine power (partial) while maneuvering
From Brawley, CA to Brawley, CA
Event
- NTSB case
- WPR16LA134
- 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
Bell OH 58A
- Aircraft type
- Bell OH-58
- Category
- Helicopter
- 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
- N6251G
- Operator
- Farm Aviation
- Onboard fatalities
- Unknown
- Route
- From Brawley, CATo Brawley, CA
- Aircraft age
- About 46 years (built 1970)
- 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 (partial)
- 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 handling/service
- Aircraft › Aircraft power plant
- Personnel issues › Task performance
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, after departing for the agricultural flight, he maneuvered the helicopter to line up with the field to be sprayed. Shortly after lining up with the field, the engine started to surge, and he saw the torque meter needle "bouncing rapidly." The pilot initiated a precautionary landing to an open field. The helicopter landed hard, which resulted in substantial damage to the tailboom and tail rotor drive shaft.
A test run of the engine revealed that the bleed valve did not close at any speed and that the engine produced less than 250 horsepower (hp). The bleed valve was disassembled, and the diaphragm was found to have several holes and cracks, and the poppet valve located in the bleed valve assembly had radial play, consistent with worn bushings. The damaged bleed valve was replaced with an overhauled bleed valve, and during a subsequent test run, the engine produced about 380 hp, which is about 7% below minimum allowable power for a serviceable engine. Given these results, the excessive wear of the bleed valve likely prevented it from closing during the accident flight, which resulted in the engine's degraded performance.
According to the operator, the compressor, turbine, and bleed valve assemblies were overhauled about 2 years before the accident and then reassembled on the engine. The engine had operated about 766 hours since overhaul at the time of the accident. The engine manufacturer reported that the bleed valve assembly should be overhauled every 1,500 hours. No component log cards or historical information for the bleed valve was located during the investigation.
According to the engine manufacturer, the bleed valve exhibited wear that was not consistent with a bleed valve with comparable service time. Therefore, it is likely that the bleed valve was likely not overhauled 2 years before the accident as reported by the operator and that it was beyond the overhaul period of 1,500 hours, which resulted in the observed wear that ultimately prevented the engine from producing sufficient power during takeoff.
Probable cause
The engine's degraded performance due to excessive wear of the engine bleed valve, which prevented it from closing during the accident flight. Contributing to the accident was the operator's failure to overhaul the bleed valve within the manufacturer-recommended interval.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record WPR16LA134
- Event ID
- 20160702X94036
- Case number
- WPR16LA134
- 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: 3471d1013bf4079808c93125227cf8e625a3ab53458de39444f9cd0fde437936; retrieved 2026-09-16T03:36:04.091Z.