WPR12LA426 · Bell 206 - B
Chesapeake Bay Helicopters Bell 206 - B · Accident: loss of lift while maneuvering
From Mammoth Yosemite Airport (MMH) to Mammoth Yosemite Airport (MMH)
Event
- NTSB case
- WPR12LA426
- 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 206 - B
- Aircraft type
- Bell 206
- 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
- N222GR
- Operator
- Chesapeake Bay Helicopters
- Onboard fatalities
- Unknown
- Route
- From Mammoth Yosemite Airport (MMH), Mammoth, CATo Mammoth Yosemite Airport (MMH), Mammoth, CA
- Aircraft age
- About 37 years (built 1975)
- 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 91: General Aviation
- 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
- 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 lift
- DamageDestroyed: beyond practical repair. Substantial: damage that affects the structure, performance or handling and normally needs major repair. Minor: less than that. Glossary
- Destroyed
Cause areas
- Aircraft › Aircraft oper/perf/capability
- Environmental issues › Conditions/weather/phenomena
- Personnel issues › Task performance
Approximate · Coordinates as recorded by the NTSB; no uncertainty radius is established.
NTSB narrative
While performing an aerial survey of transmission structures and wires in mountainous terrain at an elevation of about 7,500 feet mean sea level, the pilot initiated a climb to clear a ridge ahead. When he realized that there was no response to an increase in collective, and, with the torque nearing 100 percent, he chose to maneuver the helicopter left of a set of wires, avoid approaching terrain, and establish an approach for a precautionary landing to a dirt road. The pilot reported that, during the approach, he was unable to arrest the helicopter's descent, and, at the same time, he heard a noise that he assumed was the low rotor rpm warning. The helicopter subsequently impacted terrain just short of the road, rolled over on its left side, and was consumed by the postcrash fire. A postaccident examination of the airframe and engine revealed no mechanical anomalies that would have precluded normal operation. At the time of the accident, the nearest weather reporting facility, which was located 10.5 miles west of the accident site, reported wind at 4 knots, gusting to 14 knots, and a temperature of 24 degrees C. The calculated density altitude for the conditions was about 9,742 feet, which would have affected the helicopter's climb performance.
Probable cause
The pilot’s inability to maintain sufficient main rotor rpm while maneuvering in high density altitude conditions, which resulted in a precautionary landing and subsequent rollover.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record WPR12LA426
- Event ID
- 20120920X05155
- Case number
- WPR12LA426
- 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. 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: efe518b754ffbcca5160d0dd7cbda14b031d7d2fc69c9e4322e9c408cd9d250f; retrieved 2026-09-15T19:55:22.763Z.