# NTSB DEN05LA137: Bell 47G-3B-1, N24SD, Rock Springs, WY, September 13, 2005 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: September 13, 2005, 11:50 local (17:50 UTC) - Place: Rock Springs, WY - Coordinates: 41.602779, -109.074996 - Nearby events: https://openairdocs.org/map.md?lat=41.6028&lon=-109.0750&mi=10 - Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 2 uninjured - Status: Completed, report August 29, 2006 - Report: Approved by Office Director - Parties: FAA Flight Standards Field Office, FAA Flight Standards District Office - NTSB case key (mKey): 62448 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=DEN05LA137 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/62448/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=62448 - Page: https://openairdocs.org/ntsb/DEN05LA137 ## Probable cause the pilot's failure to maintain control of the helicopter during the attempted autorotation after he experienced an engine overspeed that occurred for reasons undetermined. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Airframe/component/system failure/malfunction, maneuvering - reason for occurrence undetermined (cause) - Forced landing, descent - emergency - autorotation - attempted, pilot in command - Hard landing, descent - emergency - flare - improper, pilot in command (cause) - terrain condition - ground ## Analysis According to the pilot, he was maneuvering at approximately 25 feet agl. The pilot stated that he heard a grinding noise and the "helicopter yawed to the right a couple of times." He stated that the engine began to overspeed and he initiated an autorotation. The pilot stated that the helicopter impacted the ground hard, resulting in substantial damage. An examination, revealed that all six shearbolts had failed. Examination of the fracture faces of the six shear bolts revealed signatures consistent with a shearing action. The examination of the helicopter airframe, engine, transmission, and remaining systems revealed no anomalies. ## Factual narrative On September 13, 2005, approximately 1150 mountain daylight time, a Bell 47G-3B-1, N24SD, operated by Helicopter Roundup Services LLC, and piloted by a commercial pilot, was substantially damaged when it impacted terrain during an autorotation near Rock Springs, Wyoming. Visual meteorological conditions prevailed at the time of the accident. The aerial herding flight was being operated under the provisions of Title 14 CFR Part 91 without a flight plan. The commercial pilot and his passenger were not injured. The local flight departed Rock Springs, approximately 1100. According to the Pilot/Operator Aircraft Accident Report form submitted by the pilot, "he was maneuvering near the trap with some horses at approximately 25" feet agl. The pilot stated he heard a grinding noise and the "helicopter yawed to the right a couple of times." He stated that the engine began to overspeed and he initiated an autorotation. The pilot stated that the helicopter impacted the ground hard, bending the landing skids and rocking the helicopter forward. The main rotor contacted the tail boom, separating the tail rotor and tail skid from the helicopter. The helicopter was recovered and relocated to a hangar in Boise, Idaho, for further examination. The helicopter airframe, engine, transmission, and remaining systems were examined under the auspices of an airworthiness inspector from the Federal Aviation Administration, Boise, Idaho, Flight Standards District Office. During the examination, it was noted that all six shearbolts had failed. These bolts were sent to the NTSB laboratory for further examination and testing. The examination of the helicopter airframe, engine, transmission, and remaining systems revealed no anomalies. Examination of the fracture faces of the six shear bolts revealed a thin crescent shaped portion with surface lines aligned in the direction indicated by the tips of the crescent. The adjacent surface displayed a rough grainy surface also displaying surface lines aligned in the direction indicated by the tips of the crescent. The shank of the bolt adjacent to the fracture face had been deformed in the direction indicated by the tips of the crescent. The features are consistent with a shearing action. Information received from the aircraft manufacturer revealed that the shear bolts should be heat treated to a hardness of 91-98 HRB (Hardness, Rockwell, "B" scale). The hardness of all the shear bolts satisfied the hardness requirement. ## Aircraft - Registration: [N24SD](https://openairdocs.org/deregistered/N24SD-2008-07-14), registration cancelled 2008-07-14, S/N 3671, built 1967 (OpenAirDocs) - Reported make and model: Bell 47G-3B-1 - 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: 3671 - Airframe hours: 8856 - Engines: Lycoming TVO-435-B1A 270 horsepower reciprocating - Damage: Substantial damage - Flight: Other work use, Part 91 - Registered owner: Helicopter Roundup Service LLC - Airworthiness certificate: Standard, Normal - Last inspection: 100 hour, August 1, 2005, 1,224 hours before - Departed: RKS, Rock Springs, WY - Airport: Na ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 42; injuries: none; commercial; medical: class 2, without waivers/limitations; last flight review June 1, 2005; seat: left; flight hours: 2,940 total, 1,540 in this make and model, 2,900 as pilot in command, 309 in the last 90 days, 116 in the last 30 days, 1 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: variable at 3 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 52 °F, dew point 21 °F - Altimeter: 30.17 inHg - Observed at: RKS, 30 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 20050913020519A](https://openairdocs.org/incident/20050913020519A), Sep 13, 2005: Bell 47G3B1, Rock Springs, WY, Substantial damage. (-23) Inspection of the aircraft revealed that the upper planetary gear in the transmission failed, this caused an engine overspeed and emergency landing.… ## Other investigations on N24SD (1) 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 LAX08LA097](https://openairdocs.org/ntsb/LAX08LA097), Apr 11, 2008: Bell 47G-3B-1 (N24SD), Denio, NV, substantial damage. Probable cause: The pilot's inadvertent hard landing induced by a perceived loss of power and a main transmission anomaly while maneuvering at low altitude. ## Docket (2 files) The files NTSB released with the investigation on June 8, 2006, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=62448. 273 KB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 244 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40466865&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Master.PDF - Supplement E (item 2, .PDF, 29 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40258696&FileExtension=.PDF&FileName=Supplement%20E-Master.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.