# Engine/transmission coupling - Type: NTSB finding subsection - Path: [Aircraft](https://openairdocs.org/ntsb-findings/01) › [Aircraft propeller/rotor](https://openairdocs.org/ntsb-findings/0104) › [Main rotor drive](https://openairdocs.org/ntsb-findings/010463) › Engine/transmission coupling - NTSB code: 01046310 - Cases: 24 - In the probable cause: 24 - Fatal cases: 4 - All cases: https://openairdocs.org/ntsb-findings/01046310/cases.md - Cases with it in the probable cause: https://openairdocs.org/ntsb-findings/01046310/cases.md?cause=1 - Page: https://openairdocs.org/ntsb-findings/01046310 ## Cases per year (in the probable cause / all) - 2008: 1 / 1 - 2010: 1 / 1 - 2011: 2 / 2 - 2012: 1 / 1 - 2013: 1 / 1 - 2014: 1 / 1 - 2015: 3 / 3 - 2016: 2 / 2 - 2017: 1 / 1 - 2018: 2 / 2 - 2019: 4 / 4 - 2020: 1 / 1 - 2021: 1 / 1 - 2022: 1 / 1 - 2023: 1 / 1 - 2024: 1 / 1 ## Defining events in these cases - [Sys/Comp malf/fail (non-power)](https://openairdocs.org/ntsb-events/330): 11 cases - [Powerplant sys/comp malf/fail](https://openairdocs.org/ntsb-events/340): 8 cases - [Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342): 2 cases - [Miscellaneous/other](https://openairdocs.org/ntsb-events/900): 1 cases - [Fire/smoke (non-impact)](https://openairdocs.org/ntsb-events/150): 1 cases - [Controlled flight into terr/obj (CFIT)](https://openairdocs.org/ntsb-events/120): 1 cases ## Aircraft models (registry) - [Robinson Helicopter R44 II](https://openairdocs.org/model/robinson-helicopter-r44-ii): 2 cases - [Robinson Helicopter R22 BETA](https://openairdocs.org/model/robinson-helicopter-r22-beta): 2 cases - [Hughes Helicopters HUGHES 369D](https://openairdocs.org/model/hughes-helicopters-hughes-369d): 2 cases - [Bell 206B](https://openairdocs.org/model/bell-206b): 2 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 - [Robinson Helicopter R44](https://openairdocs.org/model/robinson-helicopter-r44): 1 cases - [Hiller UH-12E](https://openairdocs.org/model/hiller-uh-12e): 1 cases - [Enstrom Helicopter TH-180](https://openairdocs.org/model/enstrom-helicopter-th-180): 1 cases - [Enstrom F-28F](https://openairdocs.org/model/enstrom-f-28f): 1 cases ## Other findings in the same cases - [Scheduled/routine maintenance](https://openairdocs.org/ntsb-findings/02062010) (Personnel issues): 8 cases - [Installation](https://openairdocs.org/ntsb-findings/02062035) (Personnel issues): 3 cases - [Use of equip/system](https://openairdocs.org/ntsb-findings/02063015) (Personnel issues): 2 cases - [Adherence to safety program](https://openairdocs.org/ntsb-findings/04035020) (Organizational issues): 1 cases - [Oversight of maintenance](https://openairdocs.org/ntsb-findings/04032020) (Organizational issues): 1 cases - [Equipment manufacture](https://openairdocs.org/ntsb-findings/04013010) (Organizational issues): 1 cases - [Manufacture/production, general](https://openairdocs.org/ntsb-findings/04013000) (Organizational issues): 1 cases - [Equipment design](https://openairdocs.org/ntsb-findings/04011010) (Organizational issues): 1 cases - [Snowy/icy terrain](https://openairdocs.org/ntsb-findings/03021030) (Environmental issues): 1 cases - [Water](https://openairdocs.org/ntsb-findings/03021020) (Environmental issues): 1 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 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 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 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 CEN19LA106](https://openairdocs.org/ntsb/CEN19LA106), Mar 20, 2019: Robinson R22 (N7782H), Madill, OK, substantial damage. Probable cause: The failure of the V-belts due to improper maintenance, which resulted in the loss of power to the helicopter's rotor system and subsequent forced landing on rough terrain. - [NTSB ERA19FA118](https://openairdocs.org/ntsb/ERA19FA118), Mar 5, 2019: Hughes 369 (N89ZC), Talking Rock, GA, substantial damage, 1 fatal. Probable cause: A fatigue failure of the overrunning clutch subassembly due to abnormal bending loads due to cracks on the center engine mount, which resulted in an inflight loss of power. Contributing to the… - [NTSB CEN18LA334](https://openairdocs.org/ntsb/CEN18LA334), Aug 16, 2018: Schweizer 269C (N3625Z), Kindred, ND, destroyed. Probable cause: The pilot’s failure to adequately inspect the lower coupling driveshaft during his preflight inspection and his non-compliance with an applicable airworthiness directive, which resulted in the… 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.