# NTSB CEN14LA174: Bell 47G 3B, N147WT, Oglesby, TX, March 30, 2014 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: March 30, 2014, 11:30 local (16:30 UTC) - Place: Oglesby, TX - Coordinates: 31.311388, -97.361114 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=31.3114&lon=-97.3611&mi=10 - Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping) - Defining event: [Maneuvering-low-alt flying: Powerplant sys/comp malf/fail](https://openairdocs.org/ntsb-events/340) - Highest injury: No injuries - Injuries: 2 uninjured - Status: Completed, report June 1, 2015 - Report: Approved by Office Director - NTSB office: Central Region - Parties: FAA - NTSB case key (mKey): 88989 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CEN14LA174 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/88989/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=88989 - Page: https://openairdocs.org/ntsb/CEN14LA174 ## Probable cause Maintenance personnel’s failure to safety wire the throttle control adapter per maintenance instructions when the carburetor was replaced and to detect that the adapter was not safety wired during the annual inspection, which resulted in the throttle control disconnecting and subsequent loss of engine control. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Maintenance: installation](https://openairdocs.org/ntsb-findings/02062035): Personnel issues › Task performance · Maintenance personnel (probable cause); cases with it: [Bell 47G-3B-1, 1 case](https://openairdocs.org/ntsb-findings/02062035/cases.md?model=1181028), [All aircraft, 371 cases](https://openairdocs.org/ntsb-findings/02062035/cases.md) - [Aircraft](https://openairdocs.org/ntsb-findings/01020000): Aircraft › Aircraft systems · Incorrect service/maintenance (probable cause); cases with it: [Bell 47G-3B-1, 2 cases](https://openairdocs.org/ntsb-findings/01020000/cases.md?model=1181028), [All aircraft, 63 cases](https://openairdocs.org/ntsb-findings/01020000/cases.md) - [Maintenance/inspections](https://openairdocs.org/ntsb-findings/01010500): Aircraft › Aircraft handling/service · Incorrect service/maintenance (probable cause); cases with it: [Bell 47G-3B-1, 1 case](https://openairdocs.org/ntsb-findings/01010500/cases.md?model=1181028), [All aircraft, 103 cases](https://openairdocs.org/ntsb-findings/01010500/cases.md) - [Inspection: scheduled/routine inspection](https://openairdocs.org/ntsb-findings/02061520): Personnel issues › Task performance · Maintenance personnel (probable cause); cases with it: [Bell 47G-3B-1, 1 case](https://openairdocs.org/ntsb-findings/02061520/cases.md?model=1181028), [All aircraft, 167 cases](https://openairdocs.org/ntsb-findings/02061520/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Maneuvering-low-alt flying: Powerplant sys/comp malf/fail](https://openairdocs.org/ntsb-events/340) (defining event); cases with it: [Bell 47G-3B-1, 2 cases](https://openairdocs.org/ntsb-events/340/sequence.md?model=1181028), [All aircraft, 820 cases](https://openairdocs.org/ntsb-events/340/sequence.md) - [Autorotation: Loss of control in flight](https://openairdocs.org/ntsb-events/240); cases with it: [Bell 47G-3B-1, 5 cases](https://openairdocs.org/ntsb-events/240/sequence.md?model=1181028), [All aircraft, 5,002 cases](https://openairdocs.org/ntsb-events/240/sequence.md) - [Landing-flare/touchdown: Roll over](https://openairdocs.org/ntsb-events/097); cases with it: [Bell 47G-3B-1, 2 cases](https://openairdocs.org/ntsb-events/097/sequence.md?model=1181028), [All aircraft, 261 cases](https://openairdocs.org/ntsb-events/097/sequence.md) ## Analysis The pilot reported that, during an en route climb in the helicopter, he increased the throttle and noticed a "slight resistance." Shortly after, the throttle freed up, but it was ineffective; there was no corresponding change in engine power when he moved the throttle control. Both the engine and rotor rpm were indicating in the green, but they began to decrease when he adjusted the collective. When he stopped moving the collective, the engine and rotor rpm increased rapidly and continued to accelerate. The pilot initiated an autorotation and cut off the fuel. The pilot then increased the collective, and the helicopter yawed left, touched down, and rolled over to the right, which resulted in the tailboom separating. A postaccident examination of the helicopter revealed that the throttle control adapter had disconnected from the serrated shaft on the carburetor. The retention screws on the throttle control adapter were not safety wired to the carburetor idle stop lever as required in the helicopter manufacturer's maintenance manual. A review of maintenance records revealed that the carburetor was removed and replaced about 1 1/2 years before the accident and that the helicopter's last annual inspection was conducted about 4 1/4 months before the accident. ## Factual narrative On March 30, 2014, about 1130 central daylight time, a Bell 47G-3B helicopter, N147WT, rolled over during an autorotation near Oglesby, Texas. The pilot and passenger were not injured. The helicopter was registered to and operated by Lazy 7 Agricultural Services LLC as a 14 Code of Federal Regulations Part 91 aerial observation flight. Visual meteorological conditions prevailed for the flight, which was not operated on a flight plan. The local flight originated from the Gatesville Municipal Airport (GOP), Gatesville, Texas at 1100. The pilot reported the purpose of the flight was to spot wildlife. He stated that during the flight he initiated a climb to transit from one area to another. As he increased the throttle he noticed a "slight resistance." Shortly thereafter, the throttle freed up, but there was no response to the throttle movements. The pilot stated that both the engine and rotor rpm were indicating in the green, but the rotor and engine rpm decayed when he increased the collective. When he stopped increasing the collective, the rotor and engine rpm increased rapidly and continued to accelerate. The pilot initiated an autorotation, during which time he cutoff the fuel. During the final collective application to cushion the landing, the helicopter suddenly yawed to the left and simultaneously rolled to the right on touchdown. A postaccident examination of the helicopter revealed the throttle control adapter had disconnected from the serrated shaft on the carburetor. The retention screws on the throttle control adapter were not safety wired to the carburetor idle stop lever as required in the Bell Helicopter maintenance manual. Service Bulletin 131SB was issued on December 2, 1960, which addressed the reworking the adapter screw holes and safety wiring of the adapter to the carburetor idle stop lever. This Service Bulletin addressed the Bell 47G-2 and 47J-2 models. The maintenance manual for the 47G-3B was later revised to reflect the information in the Service Bulletin. Maintenance records show the carburetor was removed and replaced on September 25, 2012, and the last annual inspection was performed November 11, 2013. ## Aircraft - Registration: [N147WT](https://openairdocs.org/aircraft/N147WT), registered now, S/N 2920, built 1964 (OpenAirDocs) - Reported make and model: BELL 47G 3B - Registry model: [Bell 47G-3B-1](https://openairdocs.org/model/bell-47g-3b-1) (registry code 1181028) (OpenAirDocs) - Registry engine: [Lycoming TVO-435-GIA](https://openairdocs.org/engine/lycoming-tvo-435-gia) (registry code 41526, turbo-prop) (OpenAirDocs) - Category: Helicopter - Serial number: 2920 - Year built: 1964 - Airframe hours: 3280 - Engines: LYCOMING TVO-435-B1 180 horsepower reciprocating - Damage: Substantial damage - Flight: Aerial observation, Part 91 - Operator: Lazy 7 Agricultural Services LLC - Registered owner: Lazy 7 Agricultural Services LLC - Airworthiness certificate: Standard, Normal - Last inspection: Annual, November 5, 2013, 30 hours before - Departed: GOP, Gatesville, TX - Destination: GOP, Gatesville, TX ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 41; injuries: minor; flight instructor, airline transport; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane; medical: class 2, without waivers/limitations; seat: left; restraint: 3-point; flight hours: 3,800 total, 54 in this make and model, 3,000 as pilot in command, 2 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 170° at 15 knots, gusting 21 - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 72 °F, dew point 46 °F - Altimeter: 30.19 inHg - Observed at: TPL, 11 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 (OpenAirDocs). - [Accident 20140330004939A](https://openairdocs.org/incident/20140330004939A), Mar 30, 2014: Bell 47G-3B-1, Oglesby, TX, Substantial damage. Pilot experienced throttle problems while flying and decided to return to his base of operations. Pilot lost throttle control of aircraft followed by an… ## Docket (5 files) The files NTSB released with the investigation on April 28, 2015, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=88989. 2.4 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 1.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40425618&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1%20-Redacted.PDF - Record of Conversation (item 2, .PDF, 68 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40425619&FileExtension=.PDF&FileName=Record%20of%20Conversation-Master.PDF - Maintenance Record (item 3, .PDF, 109 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40425620&FileExtension=.PDF&FileName=Maintenance%20Record%20%20-Redacted.PDF - Bell 47G-3B Maintenance Manual Excerpt (item 4, .PDF, 207 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40425621&FileExtension=.PDF&FileName=Bell%2047G-3B%20Maintenance%20Manual%20Excerpt-Master.PDF - Service Bulletin (item 5, .PDF, 658 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40425622&FileExtension=.PDF&FileName=Service%20Bulletin%20-Redacted.PDF 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.