# NTSB CEN18LA306: Bell 47G 3B, N347BH, Custer, SD, August 2, 2018 - Type: NTSB accident investigation - Classification: Accident · Minor injuries · Class 3 · Limited · Final report - Date: August 2, 2018, 09:20 local (15:20 UTC) - Place: Custer, SD - Coordinates: 43.825, -103.63583 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=43.8250&lon=-103.6358&mi=10 - Phase of flight: [Approach](https://openairdocs.org/ntsb-phases/500) (OpenAirDocs' grouping) - Defining event: [Approach: Loss of control in flight](https://openairdocs.org/ntsb-events/240) - Highest injury: Minor injuries - Injuries: 1 minor, 2 uninjured - Status: Completed - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Central Region - Parties: FAA - NTSB case key (mKey): 97971 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CEN18LA306 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/97971/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=97971 - Page: https://openairdocs.org/ntsb/CEN18LA306 ## Probable cause The pilot’s mismanagement of rotor RPM and subsequent forced landing on uneven terrain which led to a dynamic rollover. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Action: delayed action](https://openairdocs.org/ntsb-findings/02041025): Personnel issues › Action/decision · Pilot (probable cause); cases with it: [Bell 47G-3B, 1 case](https://openairdocs.org/ntsb-findings/02041025/cases.md?model=1181026), [All aircraft, 894 cases](https://openairdocs.org/ntsb-findings/02041025/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Approach: Loss of control in flight](https://openairdocs.org/ntsb-events/240) (defining event); cases with it: [Bell 47G-3B, 7 cases](https://openairdocs.org/ntsb-events/240/sequence.md?model=1181026), [All aircraft, 5,002 cases](https://openairdocs.org/ntsb-events/240/sequence.md) - [Landing: Dynamic rollover](https://openairdocs.org/ntsb-events/231); cases with it: [Bell 47G-3B, 1 case](https://openairdocs.org/ntsb-events/231/sequence.md?model=1181026), [All aircraft, 161 cases](https://openairdocs.org/ntsb-events/231/sequence.md) ## Analysis The commercial-rated pilot and flight instructor were completing familiarization training in the accident helicopter. After successful training flights the morning of the accident, the flight instructor decided to remove the dual controls from the helicopter, and one additional passenger was loaded before practicing hovering and a low-rpm recovery. On approach to land during the accident flight, about 100 feet above ground level (agl), the pilot noticed the rotor rpms drop below the normal operating range. The pilot increased throttle but was unable to recover rotor rpms within the normal range. The flight instructor stated that the helicopter lost a lot of altitude quickly and there was no time to recover. The pilot attempted a forced landing on the side of a roadway but caught the right skid on uneven ground, which led to a dynamic rollover and substantially damaged the tail section and tail rotor. The flight instructor stated that the engine had no mechanical anomalies before the flight and that the engine had “performed well” during both the accident flight and previous flights. The helicopter likely lost power and altitude due to the pilot’s mismanagement of rotor rpm resulting in the pilot having to attempt a forced landing on uneven terrain and a subsequent dynamic rollover. ## Factual narrative On August 2, 2018, about 0920 mountain daylight time, a Bell 47G 3B helicopter, N347BH, was substantially damaged when it was involved in an accident near Custer, South Dakota. The pilot and passenger were not injured; the flight instructor received minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. The commercial-rated pilot and flight instructor completed several training flights in the accident helicopter before the accident flight to familiarize the pilot with Bell 47 helicopters. On the morning of the accident, the pilot completed hover practice and three circuits in the pattern at Crazy Horse Heliport (0SD9), Custer, South Dakota. Because the instructor did not intervene during the pattern work, the dual flight controls were removed to allow for additional occupants and for the accident pilot to practice flying with a heavier load like the pilot would encounter during future tour flight operations. After picking up a passenger, the pilot and flight instructor practiced hovering and a low-rpm recovery. The helicopter departed 0SD9 and followed a left traffic pattern. On the approach to land, about 100 feet agl, the pilot stated she noticed the rotor rpms drop below the normal operating range. She increased throttle but was unable to recover rotor rpms within normal range. The flight instructor stated that the helicopter lost a lot of altitude quickly and there was no time to recover. He also explained that the turbocharger on the engine had “some lag, the rotor rpm does not come back up with only opening the throttle but lowering the collective at that time was not an option due to the low altitude.” The helicopter continued to descend toward the ground with oncoming traffic on the road. The pilot executed a forced landing in a grassy area on the side of a highway. However, the right skid caught on uneven ground and the helicopter rolled over to the right on the sloping terrain, which substantially damaged the tail section and tail rotor. The flight instructor stated that the engine did not “shutter,” “kick,” or demonstrate another anomaly before or during the event and that the engine “performed well.” He also recalled that the engine did not have issues on any of the previous flights. ## Aircraft - Registration: [N347BH](https://openairdocs.org/aircraft/N347BH), registered now, S/N 2771, built 1962 (OpenAirDocs) - Reported make and model: BELL 47G 3B (No Series) - Registry model: [Bell 47G-3B](https://openairdocs.org/model/bell-47g-3b) (registry code 1181026) (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: 2771 - Year built: 1962 - Airframe hours: 1998.1 - Engines: Lycoming TVO-435D1B 270 horsepower reciprocating - Damage: Substantial damage - Flight: Instructional, Part 91 - Operator: Black Hill Aerial Adventure - Registered owner: Dakota Rotors - Airworthiness certificate: Standard, Normal - Last inspection: 100 hour, January 1, 2018, 47.8 hours before - Departed: OSD9, Custer, SD - Destination: Same as departure - Airport: OSD9, Crazy Horse Base ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 32; injuries: none; commercial, flight instructor; instrument ratings: helicopter; medical: class 2, with waivers/limitations; last flight review May 23, 2018; seat: left; restraint: 4-point; flight hours: 1,063 total, 2 in this make and model, 884 as pilot in command, 176 in the last 90 days, 86 in the last 30 days, 7 in the last 24 hours - Pilot-rated passenger; injuries: minor; flight instructor, foreign, commercial; seat: center; restraint: lap only; flight hours: 1,100 total ## Weather - Conditions: Visual (VMC), Day - Wind: 320° at 3 knots - Visibility: 10 statute miles - Temperature: 75 °F, dew point 32 °F - Altimeter: 30.07 inHg - Observed at: KCUT, 405 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 20180802009539A](https://openairdocs.org/incident/20180802009539A), Aug 2, 2018: Bell 47G-3B, Substantial damage. On 08/02/2018 approximatly 0830 a helicopter registered to dakota rotors LLC landed on uneven terrian after the pilot stated the RPM dropped and was unable to… ## Other investigations on N347BH (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 ERA26LA100](https://openairdocs.org/ntsb/ERA26LA100), Jan 29, 2026: Bell 47G-3B (N347BH), Floral City, FL, destroyed. Probable cause: The student pilot’s loss of helicopter control during landing. ## Docket (4 files) The files NTSB released with the investigation on April 19, 2021, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=97971. 13.2 MB in all. - Pilot/operator aircraft accident report, NTSB form 6120.1 (student) (item 1, PDF, 9 pages, 6.6 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11720353&FileExtension=pdf&FileName=CEN18LA306%20Atwater%20completed%206120_Redacted-Rel.pdf - Pilot/operator aircraft accident report, NTSB form 6120.1 (instructor) (item 2, PDF, 11 pages, 2.0 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11720154&FileExtension=pdf&FileName=CEN18LA306%20Bohren%206120%20completed%20w%20blocks-Rel.pdf - Memorandum of record interview with instructor pilot (item 3, PDF, 1 page, 130 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11719631&FileExtension=pdf&FileName=Memorandum%20of%20Record%20Interview%20with%20Instructor%20Pilot-Rel.pdf - Photographs of accident helicopter (item 4, PDF, 2 pages, 4.4 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11757989&FileExtension=pdf&FileName=Photos%20for%20Docket-Rel.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.