# Main rotor drive - Type: NTSB finding section - Path: [Aircraft](https://openairdocs.org/ntsb-findings/01) › [Aircraft propeller/rotor](https://openairdocs.org/ntsb-findings/0104) › Main rotor drive - NTSB code: 010463 - Cases: 44 - In the probable cause: 41 - Fatal cases: 6 - All cases: https://openairdocs.org/ntsb-findings/010463/cases.md - Cases with it in the probable cause: https://openairdocs.org/ntsb-findings/010463/cases.md?cause=1 - Page: https://openairdocs.org/ntsb-findings/010463 ## Cases per year (in the probable cause / all) - 2008: 5 / 6 - 2009: 2 / 2 - 2010: 2 / 2 - 2011: 4 / 4 - 2012: 2 / 2 - 2013: 1 / 1 - 2014: 2 / 2 - 2015: 3 / 4 - 2016: 3 / 3 - 2017: 2 / 2 - 2018: 4 / 4 - 2019: 4 / 4 - 2020: 2 / 2 - 2021: 1 / 2 - 2022: 1 / 1 - 2023: 2 / 2 - 2024: 1 / 1 ## Findings - [Engine/transmission coupling](https://openairdocs.org/ntsb-findings/01046310): 24 cases, 24 in the probable cause - [Main rotor drive, general](https://openairdocs.org/ntsb-findings/01046300): 15 cases, 13 in the probable cause - [Main rotor gearbox](https://openairdocs.org/ntsb-findings/01046320): 2 cases, 2 in the probable cause - [Main rotor brake](https://openairdocs.org/ntsb-findings/01046321): 1 cases, 0 in the probable cause - [Main rotor trans mount](https://openairdocs.org/ntsb-findings/01046330): 1 cases, 1 in the probable cause - [Rotor/drive indicating system](https://openairdocs.org/ntsb-findings/01046340): 1 cases, 1 in the probable cause ## Defining events in these cases - [Sys/Comp malf/fail (non-power)](https://openairdocs.org/ntsb-events/330): 20 cases - [Powerplant sys/comp malf/fail](https://openairdocs.org/ntsb-events/340): 9 cases - [Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342): 5 cases - [Loss of control in flight](https://openairdocs.org/ntsb-events/240): 2 cases - [Miscellaneous/other](https://openairdocs.org/ntsb-events/900): 1 cases - [Off-field or emergency landing](https://openairdocs.org/ntsb-events/440): 1 cases - [Loss of engine power (total)](https://openairdocs.org/ntsb-events/341): 1 cases - [Flight control sys malf/fail](https://openairdocs.org/ntsb-events/333): 1 cases - [Loss of control on ground](https://openairdocs.org/ntsb-events/230): 1 cases - [Fire/smoke (non-impact)](https://openairdocs.org/ntsb-events/150): 1 cases ## Aircraft models (registry) - [Robinson Helicopter R44 II](https://openairdocs.org/model/robinson-helicopter-r44-ii): 4 cases - [Robinson Helicopter R22 BETA](https://openairdocs.org/model/robinson-helicopter-r22-beta): 4 cases - [Robinson Helicopter R44](https://openairdocs.org/model/robinson-helicopter-r44): 3 cases - [Bell 206B](https://openairdocs.org/model/bell-206b): 3 cases - [Hughes Helicopters HUGHES 369D](https://openairdocs.org/model/hughes-helicopters-hughes-369d): 2 cases - [Hiller UH-12E](https://openairdocs.org/model/hiller-uh-12e): 2 cases - [Gaddis Michael EXEC 162-F](https://openairdocs.org/model/gaddis-michael-exec-162-f): 2 cases - [Eurocopter France SA330J](https://openairdocs.org/model/eurocopter-france-sa330j): 1 cases - [Eurocopter AS 350 B2](https://openairdocs.org/model/eurocopter-as-350-b2): 1 cases - [Schweizer HUGHES 269C](https://openairdocs.org/model/schweizer-hughes-269c): 1 cases ## Other findings in the same cases - [Scheduled/routine maintenance](https://openairdocs.org/ntsb-findings/02062010) (Personnel issues): 9 cases - [Aircraft control](https://openairdocs.org/ntsb-findings/02063040) (Personnel issues): 5 cases - [Installation](https://openairdocs.org/ntsb-findings/02062035) (Personnel issues): 4 cases - [Not determined, general](https://openairdocs.org/ntsb-findings/05000000) (Not determined): 3 cases - [Sloped/uneven terrain](https://openairdocs.org/ntsb-findings/03021017) (Environmental issues): 2 cases - [Use of equip/system](https://openairdocs.org/ntsb-findings/02063015) (Personnel issues): 2 cases - [Scheduled/routine inspection](https://openairdocs.org/ntsb-findings/02061520) (Personnel issues): 2 cases - [Incorrect action performance](https://openairdocs.org/ntsb-findings/02041015) (Personnel issues): 2 cases - [Landing flare](https://openairdocs.org/ntsb-findings/01062041) (Aircraft): 2 cases - [Directional control](https://openairdocs.org/ntsb-findings/01062020) (Aircraft): 2 cases ## Newest cases - [NTSB ANC24LA017](https://openairdocs.org/ntsb/ANC24LA017), Feb 27, 2024: MD Helicopter 369E/500E (N633JH), Kekaha, HI, substantial damage. Probable cause: Maintenance personnel’s noncompliance with maintenance manual procedures that required the removal of the overrunning clutch output bearing during the regreasing procedure, which resulted in… - [NTSB WPR24LA067](https://openairdocs.org/ntsb/WPR24LA067), Dec 24, 2023: Bell 206B (N111PM), El Centro, CA, substantial damage. Probable cause: An in-flight failure of the engine-to-transmission driveshaft due to a fatigue fracture of the forward-most flex plate in the forward KAflex coupling that resulted from a loose bolt attachment… - [NTSB ERA23LA293](https://openairdocs.org/ntsb/ERA23LA293), Jul 9, 2023: Hughes 369D (N5027P), Waldorf, MD, substantial damage. Probable cause: Fatigue failure of the overrunning clutch outer race and a subsequent inflight loss of power due to abnormal bending loads as a result of improper reassembly of the clutch subassembly following… - [NTSB ERA22LA256](https://openairdocs.org/ntsb/ERA22LA256), May 26, 2022: Robinson Helicopter R44 (N132TC), North Myrtle Beach, SC, substantial damage. Probable cause: The fractured attachment lug on the forward clutch shaft yoke due to fatigue failure with multiple origins. - [NTSB WPR21LA320](https://openairdocs.org/ntsb/WPR21LA320), Aug 14, 2021: Robinson Helicopter R22 Beta (N226WM), West Jordan, UT, substantial damage. Probable cause: The pilot receiving instruction’s improper application of forward cyclic in a low rotor rpm condition and the instructor’s delayed remediation, which resulted in an impact with terrain. - [NTSB ANC21LA038](https://openairdocs.org/ntsb/ANC21LA038), May 9, 2021: Enstrom F-28F (N8627J), Palmer, AK, substantial damage. Probable cause: A loss of drive to the rotor system due to the disengagement of the main belt drive tensioning system, which resulted in a forced landing. The disengagement was due to inadequate clearance between… - [NTSB CEN20LA330](https://openairdocs.org/ntsb/CEN20LA330), Aug 8, 2020: Robinson R44 (N89LA), Logan, IA, substantial damage. Probable cause: The failure of the lower actuator bearing support brackets, which resulted in the misalignment of the clutch actuator, a loss of belt tension on the main rotor drive system, and a subsequent forced… - [NTSB WPR20LA228](https://openairdocs.org/ntsb/WPR20LA228), Jul 20, 2020: Md Helicopter 600 (N745BW), San Andreas, CA, destroyed. Probable cause: The failure of the output shaft of the overrunning clutch inner race due to frictional overheating of the shaft, which resulted from the failure of the output bearing’s stainless-steel grease seal. - [NTSB ERA20LA054](https://openairdocs.org/ntsb/ERA20LA054), Dec 14, 2019: Robinson R44 (N440AH), San Antonio, TX, substantial damage. Probable cause: Maintenance personnel’s failure to complete all necessary steps of a service bulletin and subsequent failure to identify the loose lower actuator bearing support bracket during inspections, which… - [NTSB CEN19LA240](https://openairdocs.org/ntsb/CEN19LA240), Jul 27, 2019: Robinson R44 (N7508Z), Blair, NE, substantial damage. Probable cause: The failure of the lower actuator bearing support bracket, which resulted in the misalignment of the clutch actuator, the loss of belt tension on the main rotor drive system, and the subsequent… NTSB has coded findings and defining events since 2008; earlier cases used its older occurrence and cause codes and aren't counted. Findings: https://openairdocs.org/ntsb-findings.md. Defining events: https://openairdocs.org/ntsb-events.md. Phases of flight: https://openairdocs.org/ntsb-phases.md. Every investigation, filtered by finding, event, phase, state, year or model: https://openairdocs.org/ntsb.md (for example ?state=MI&fatal=1). NTSB's definitions: Accident and incident, 49 CFR 830.2 (https://www.ecfr.gov/current/title-49/subtitle-B/chapter-VIII/part-830/subpart-A/section-830.2), CICTT occurrence categories (PDF) (https://www.ntsb.gov/safety/data/Documents/datafiles/OccurrenceCategoryDefinitions.pdf), CICTT phases of flight (PDF) (https://www.ntsb.gov/safety/data/Documents/datafiles/PhaseofFlightDefinitions.pdf), and NTSB coding manual, before 2008 (PDF) (https://www.ntsb.gov/GILS/Documents/codman.pdf). NTSB publishes no definitions for its findings, only their names. --- 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.