- Date
- April 18, 1990, 09:30 local (14:30 UTC)
- Place
- Oakdale, MN
- Injuries
- 1 serious
- Damage
- Substantial damage
- Phase of flight
- Enroute
- Aircraft
- N5120BBell 47
- Weather
- Visual (VMC) · Day
- Status
- Completed · report September 28, 1992
- Report
- Approved by Office Director
- FAA report
- 19900418010139A
- Case key
- 34963
From the NTSB’s public API. By law, NTSB reports can’t be used as evidence in lawsuits over the accident.
On this page
Probable cause
A slipping rotor drive clutch assembly due to improper maintenance by company personnel. Contributing factors were static wires in the path.
Sequence of events
NTSB’s coding before 2008: each occurrence and phase of flight, and the causes and factors under it. The codes are defined in NTSB’s coding manual.
Analysis
While ferrying the helicopter to conduct an aerial application operation, the plt said that the engine began to overspeed. The plt entered an autorotation to reduce engine RPM, but had to clear power lines. Using the rotor RPM to clear the power lines, the rotor RPM decayed and the acft dropped in from about 50 to 75 feet AGL. Post accident investigation revealed a malfunctioning main transmission centrifugal clutch. The powerplant test failed to reveal any malfunction. An annual inspection had been performed 6 days and 4 hours of flight time prior to the accident.
Aircraft
- Registration
- N5120B
- Reported as
- Bell 47
- Category
- Helicopter
- Serial number
- 1941
- Airframe hours
- 4,610
- Engine
- Lycoming VO-435-A1F, 260 horsepower, reciprocating
- Damage
- Substantial damage
- Flight
- Aerial application · Part 137
- Operator
- Twin City Helicopters, Inc.
- Registered owner
- Jims Aviation Services, Ltd
- Airworthiness certificate
- Special, Restricted (Special)
- Last inspection
- Annual · April 12, 1990 · 4 hours before
- Airport
- NONE
Matched to the registry by N-number and the event date; the registry’s history has gaps, so older matches can be wrong. Compare the reported make and model.
Flight crew
As NTSB recorded them. NTSB leaves out names.
- Role
- Pilot
- Age
- 43
- Certificates
- Commercial, Flight instructor
- Airplane ratings
- Single-engine sea, Multi-engine land, Single-engine land
- Instrument ratings
- Airplane
- Medical
- Class 2, Valid Medical--w/ waivers/lim
- Seat
- Left
- Flight hours
- 4,100 total · 1,200 in this make and model · 3,900 as pilot in command
Weather
- Conditions
- Visual (VMC) · Day
- Wind
- 220° at 14 knots
- Visibility
- 15 statute miles
- Lowest ceiling
- None
- Temperature
- 48 °F, dew point 19 °F
- Altimeter
- 30.00 inHg
- Observed at
- MSP, 4 nm away
FAA reports on this event · 1
The FAA’s own accident and incident reports, matched to the aircraft by N-number and date.