# NTSB LAX03LA236: Bell 47G-2A, N4774S, Porterville, CA, July 20, 2003 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: July 20, 2003, 01:30 local (08:30 UTC) - Place: Porterville, CA - Coordinates: 36.131668, -119.214996 - Nearby events: https://openairdocs.org/map.md?lat=36.1317&lon=-119.2150&mi=10 - Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report October 28, 2004 - Report: Approved by Office Director - Parties: Federal Aviation Administration - NTSB case key (mKey): 57536 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=LAX03LA236 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/57536/pdf - Page: https://openairdocs.org/ntsb/LAX03LA236 ## 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 In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Airframe/component/system failure/malfunction, maneuvering - aerial application - rotor drive system,main gearbox/transmission - fatigue (cause) - rotor drive system,main gearbox/transmission - failure,total (cause) - In flight collision with terrain/water, descent - uncontrolled - terrain condition - rough/uneven - Roll over, descent - uncontrolled ## 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](https://openairdocs.org/deregistered/N4774S-2018-03-15), registration cancelled 2018-03-15, S/N WAV182, built 1965 (OpenAirDocs) - Reported make and model: Bell 47G-2A - Registry model: [Bell 47G-2A](https://openairdocs.org/model/bell-47g-2a) (registry code 1181012) (OpenAirDocs) - Registry engine: [Lycoming VO-435 series](https://openairdocs.org/engine/lycoming-vo-435-series) (registry code 41525, reciprocating) (OpenAirDocs) - Category: Helicopter - Serial number: WAV182 - Airframe hours: 2800 - Engines: 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 ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 38; injuries: none; 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) From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. - [NTSB WPR15LA116](https://openairdocs.org/ntsb/WPR15LA116), Feb 27, 2015: Bell 47G 2A (N4774S), Ivanhoe, CA, substantial damage. Probable cause: The pilot’s failure to maintain clearance from a power line while maneuvering at low altitude. - [NTSB MIA77DLD51](https://openairdocs.org/ntsb/MIA77DLD51), Apr 19, 1977: EL Tomcat MK6A (N4774S), Lake Wales, FL, substantial damage From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.