- Date
- July 20, 2003, 01:30 local (08:30 UTC)
- Place
- Porterville, CA
- Injuries
- 1 uninjured
- Damage
- Substantial damage
- Phase of flight
- Maneuvering
- Aircraft
- N4774SBell 47G-2A
- Weather
- Visual (VMC) · Night/dark
- Status
- Completed · report October 28, 2004
- Report
- Approved by Office Director
- Parties
- Federal Aviation Administration
- Case key
- 57536
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
Fatigue-induced failure of bolts in the helicopter's rotor drive flange, which resulted in a total loss of torque to the rotor drive shaft.
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
During an agricultural spray flight, when the helicopter's drive system disconnected from the engine, the helicopter yawed and descended about 10 feet into the underlying cotton field. The helicopter rolled upon impacting the uneven terrain. Prior to the event, the pilot heard the transmission make a loud noise and the engine oversped. The helicopter's drive system was examined, and 12 bolts on the planetary gear flange were found broken due to fatigue.
Factual narrative
On July 20, 2003, about 0130 Pacific daylight time, a Bell 47G-2A, N4774S, experienced a mechanical malfunction while maneuvering during an agricultural spray flight about 10 miles west of Porterville, California. The helicopter descended 10 feet, impacted the cotton field, rolled over, and was substantially damaged. The commercial pilot was not injured. The helicopter was operated by John Slykerman Ag Aviation, Inc., Bakersfield, California, under the provisions of 14 CFR Part 137. Visual meteorological conditions prevailed. The flight originated from the field about midnight.
The pilot reported to the National Transportation Safety Board investigator that during the flight he heard the engine's transmission make a loud noise and "disengage." Thereafter, the engine oversped as the helicopter suddenly yawed left. The pilot stated that he immediately attempted to land. The helicopter impacted the underlying field that had an uneven surface, and the helicopter rolled over.
The helicopter rotor drive system was subsequently examined. The Federal Aviation Administration investigator verbally reported that the examination revealed 12 bolts on the planetary gear flange were found broken due to fatigue.
Aircraft
- Registration
- N4774S
- Reported as
- Bell 47G-2A
- Category
- Helicopter
- Serial number
- WAV182
- Airframe hours
- 2,800
- Engine
- Lycoming VO-435-A1F, 265 horsepower, reciprocating
- Damage
- Substantial damage
- Flight
- Aerial application · Part 137
- Operator
- Johns Aerial Spraying
- Registered owner
- Sky Tech Corp. of Minnesota, Inc.
- Airworthiness certificate
- Standard, Normal
- Last inspection
- Annual · July 17, 2002 · 78 hours before
- Departed
- Porterville, CA
- Destination
- Porterville, CA
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
- 38
- Injuries
- None
- Certificates
- Flight instructor, Commercial
- Airplane ratings
- Single-engine land
- Medical
- Class 2, Valid Medical--no waivers/lim.
- Last flight review
- January 5, 2003
- Seat
- Center
- Flight hours
- 5,500 total · 3,000 in this make and model · 5,400 as pilot in command · 120 in the last 90 days · 30 in the last 30 days · 4 in the last 24 hours
Weather
- Conditions
- Visual (VMC) · Night/dark
- Wind
- 140° at 6 knots
- Visibility
- 10 statute miles
- Lowest ceiling
- None
- Temperature
- 75 °F, dew point 59 °F
- Altimeter
- 29.90 inHg
- Observed at
- PVT, 10 nm away
Other investigations on N4774S · 2
Matched to the same aircraft by N-number and date.