- Date
- August 9, 1991, 07:50 local (12:50 UTC)
- Place
- Maple Grove, MN
- Injuries
- 1 uninjured
- Damage
- Substantial damage
- Phase of flight
- Enroute
- Aircraft
- N73998Bell 47G-3B-1
- Weather
- Visual (VMC) · Day
- Status
- Completed · report April 23, 1993
- Report
- Approved by Office Director
- FAA report
- 19910809033109A
- Case key
- 14859
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
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.
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
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.'
Aircraft
- Registration
- N73998
- Reported as
- Bell 47G-3B-1
- Category
- Helicopter
- Serial number
- 2902
- Airframe hours
- 6,015
- Engine
- Allison 250-C18C, 260 horsepower, turbo shaft
- Damage
- Substantial damage
- Flight
- Aerial application · Part 137
- Operator
- Churchill, Scott
- Registered owner
- Churchill, Scott
- Airworthiness certificate
- Standard, Normal
- Last inspection
- Annual · April 15, 1991 · 122 hours before
- Departed
- MIC · Minneapolis, MN
- Destination
- NONE · MN
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
- 49
- Certificates
- Flight instructor, Commercial, Private
- Airplane ratings
- Single-engine land
- Instrument ratings
- Airplane
- Medical
- Class 2, Valid Medical--w/ waivers/lim
- Seat
- Left
- Flight hours
- 1,522 total · 1,142 in this make and model · 144 in the last 90 days · 60 in the last 30 days
Weather
- Conditions
- Visual (VMC) · Day
- Wind
- 180° at 5 knots
- Visibility
- 7 statute miles
- Lowest ceiling
- None
- Temperature
- 75 °F
FAA reports on this event · 1
The FAA’s own accident and incident reports, matched to the aircraft by N-number and date.
Other investigations on N73998 · 4
Matched to the same aircraft by N-number and date.