CHI91DER13 · Bell 47G-3B-1
Bell 47G-3B-1 · Accident: partial loss of engine power (mechanical failure) en route
From Crystal Airport (MIC) to MN (no airport)
Event
- NTSB case
- CHI91DER13
- 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
Bell 47G-3B-1
- Aircraft type
- Bell 47
- 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
- N73998
- Operator
- Churchill, Scott · private individual
- Onboard fatalities
- Unknown
- Route
- From Crystal Airport (MIC), Minneapolis, MNTo MN (no airport)
- Aircraft age
- Not recorded
- 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
- En route · cruise
- First occurrenceThe 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
- Partial loss of engine power (mechanical 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
- Pilot in command › Aircraft control, not maintained
Approximate · Coordinates as recorded by the NTSB; no uncertainty radius is established.
NTSB narrative
THE PLT SAID HE HAD COMPLETED AERIAL APPLICATION OF MOSQUITO CTL TREATMENT & WAS RTRNG TO THE LOAD SITE. THE HELICOPTER WAS IN CRUISE FLT AT 300 FT ABV THE GND WHEN THE PLT '...NOTICED IT WAS REQUIRING MORE RIGHT CYCLIC CONTROL TO KEEP THE HELICOPTER LEVEL, ALSO BEGAN TO EXPERIENCE A LOSS IN ALTITUDE.' THE PLT NOTED THE ROTOR RPM HAD DROPPED TO 90%, BUT THERE WERE NO WARNING LIGHTS OR HORNS. THE ENG OUT AUDIO WARNING WAS PLACARDED 'INOPERATIVE' & THE PLT WAS AWARE THE OIL CHIP WARNING LIGHT WAS INOP. THE PLT MADE A FORCED LANDING IN AN ALFALFA FIELD. HE STATED '...DUE TO THE RIGHT CYCLIC INPUT I HAD TO LAND WITH A DRIFT TO THE RIGHT...THE RIGHT SKID GEAR SNAPPED, ROLLING OVER TO THE RIGHT.' AN INV REVEALED THE LEFT HOPPER WAS BLOCKED & STILL CONTAINED AN ESTD 100 TO 300 LBS OF MOSQUITO CONTROL AGENT. THIS LOAD RESULTED IN AN IMBALANCE WHICH WAS COUNTERED BY EXTREME CYCLIC INPUT. EXAM OF THE ENG REVEALED 'SEVERE EROSION' OF THE COMPRESSOR BLADES, AND HORSEPOWER PRODUCTION 'SIGNIFICANTLY BELOW PRODUCTION TEST SPECIFICATIONS.'
Probable cause
THE PILOT'S FAILURE TO MAINTAIN DIRECTIONAL CONTROL OF THE HELICOPTER DURING THE FORCED LANDING. RELATED FACTORS ARE THE LOSS OF ENGINE POWER, LOSS OF ROTOR RPM, THE ERODED COMPRESSOR BLADES, THE PILOT'S OPERATION WITH KNOWN DEFICIENCIES IN EQUIPMENT AND INADEQUATE AIRCRAFT PREFLIGHT, AND THE BLOCKED SPRAY EQUIPMENT.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record CHI91DER13
- Event ID
- 20001212X17795
- Case number
- CHI91DER13
- Dataset
- historical-pre2008
- Source SHA-256
- 89e2df6d848e7ab3b42e7d7c7a03ff403303057a26ca04c95b3ea67201c3ce74
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: 3f8ef2abc9970959e070cd5530bc8f477915515f44d9d43d580374f8530452b9; retrieved 2026-09-23T03:49:27.522Z.