# Tail rotor gearbox - Type: NTSB finding subsection - Path: [Aircraft](https://openairdocs.org/ntsb-findings/01) › [Aircraft propeller/rotor](https://openairdocs.org/ntsb-findings/0104) › [Tail rotor drive system](https://openairdocs.org/ntsb-findings/010465) › Tail rotor gearbox - NTSB code: 01046520 - Cases: 12 - In the probable cause: 12 - Fatal cases: 1 - All cases: https://openairdocs.org/ntsb-findings/01046520/cases.md - Cases with it in the probable cause: https://openairdocs.org/ntsb-findings/01046520/cases.md?cause=1 - Page: https://openairdocs.org/ntsb-findings/01046520 ## Cases per year (in the probable cause / all) - 2008: 2 / 2 - 2012: 2 / 2 - 2013: 2 / 2 - 2015: 2 / 2 - 2016: 1 / 1 - 2020: 1 / 1 - 2021: 1 / 1 - 2022: 1 / 1 ## Defining events in these cases - [Part(s) separation from AC](https://openairdocs.org/ntsb-events/338): 5 cases - [Sys/Comp malf/fail (non-power)](https://openairdocs.org/ntsb-events/330): 3 cases - [Miscellaneous/other](https://openairdocs.org/ntsb-events/900): 1 cases - [Aircraft structural failure](https://openairdocs.org/ntsb-events/337): 1 cases - [Flight control sys malf/fail](https://openairdocs.org/ntsb-events/333): 1 cases - [Loss of tail rotor effectiveness](https://openairdocs.org/ntsb-events/242): 1 cases ## Aircraft models (registry) - [Hiller UH-12E](https://openairdocs.org/model/hiller-uh-12e): 2 cases - [Sikorsky S-76A](https://openairdocs.org/model/sikorsky-s-76a): 1 cases - [Robinson Helicopter R44 II](https://openairdocs.org/model/robinson-helicopter-r44-ii): 1 cases - [Robinson Helicopter R44](https://openairdocs.org/model/robinson-helicopter-r44): 1 cases - [Robinson Helicopter R22 MARINER](https://openairdocs.org/model/robinson-helicopter-r22-mariner): 1 cases - [Garlick Helicopters UH-1H](https://openairdocs.org/model/garlick-helicopters-uh-1h): 1 cases - [Bell UH-1E](https://openairdocs.org/model/bell-uh-1e): 1 cases - [Bell UH-1H](https://openairdocs.org/model/bell-uh-1h): 1 cases - [Bell-Continental Copters 47G2](https://openairdocs.org/model/bell-continental-copters-47g2): 1 cases ## Other findings in the same cases - [Tail rotor blade](https://openairdocs.org/ntsb-findings/01046410) (Aircraft): 3 cases - [Not determined, general](https://openairdocs.org/ntsb-findings/05000000) (Not determined): 1 cases - [Object/animal/substance, general](https://openairdocs.org/ntsb-findings/03022000) (Environmental issues): 1 cases - [Mountainous/hilly terrain](https://openairdocs.org/ntsb-findings/03021010) (Environmental issues): 1 cases - [Repair](https://openairdocs.org/ntsb-findings/02062015) (Personnel issues): 1 cases - [Scheduled/routine maintenance](https://openairdocs.org/ntsb-findings/02062010) (Personnel issues): 1 cases - [Descent rate](https://openairdocs.org/ntsb-findings/01062037) (Aircraft): 1 cases - [Tail rotor drive system, general](https://openairdocs.org/ntsb-findings/01046500) (Aircraft): 1 cases ## Newest cases - [NTSB WPR22LA084](https://openairdocs.org/ntsb/WPR22LA084), Jan 23, 2022: Bell UH-1E (N333XL), Gustine, CA, substantial damage. Probable cause: Failure of the 90° gearbox due to the lack of lubricating oil, which resulted in a loss of rotational drive to the tail rotor and a subsequent loss of control of the helicopter. - [NTSB ERA21LA386](https://openairdocs.org/ntsb/ERA21LA386), Sep 29, 2021: Hiller UH-12E (N430NR), Millen, GA, substantial damage. Probable cause: The improper reassembly of the tail rotor gearbox following maintenance, which resulted in fatigue failure of the input pinion gear shaft, and the subsequent loss of tail rotor drive. - [NTSB ERA20LA310](https://openairdocs.org/ntsb/ERA20LA310), Sep 6, 2020: Robinson R22 (N194HC), Fort Myers, FL, substantial damage. Probable cause: Foreign object damage of the turning tailrotor by a soft-bodied object, which resulted in the sudden stoppage of the tailrotor and the catastrophic failure of the tailrotor assembly and its mount… - [NTSB WPR17LA002](https://openairdocs.org/ntsb/WPR17LA002), Oct 5, 2016: Tamarack Helicopters UH-1H (N175SF), Gila Bend, AZ, substantial damage. Probable cause: The separation of the 90° tail rotor gearbox assembly as a result of fatigue to the tail rotor gearbox input quill assembly attachment studs due to the helicopter experiencing highly repetitive… - [NTSB ANC15LA073](https://openairdocs.org/ntsb/ANC15LA073), Sep 19, 2015: Robinson Helicopter R44 (N7162R), Fort Glenn, AK, substantial damage. Probable cause: The separation of the tail rotor gearbox from the tailboom attachment point due to overstress loads imposed by a tail rotor blade imbalance as the result of impact with an undetermined object during… - [NTSB CEN15LA379](https://openairdocs.org/ntsb/CEN15LA379), Aug 25, 2015: Robinson Helicopter R44 II (N444KD), Ketchum, OK, substantial damage. Probable cause: The separation of the tail rotor gearbox from the tailboom aft bulkhead due to overstress loads imposed by a blade imbalance from an in-flight impact with an undetermined object. - [NTSB ANC13TA076](https://openairdocs.org/ntsb/ANC13TA076), Aug 8, 2013: Bell UH-1B (N70NW), Tok, AK, substantial damage. Probable cause: The failure of the tail rotor crosshead bearing, which resulted in a loss of tail rotor control. - [NTSB CEN13FA192](https://openairdocs.org/ntsb/CEN13FA192), Mar 15, 2013: Sikorsky S-76A++ (N574EH), Grand Lake, LA, destroyed, 3 fatal. Probable cause: Fracture of the red tail rotor blade spar, which resulted in the separation and departure of the red tail rotor blade from the helicopter and subsequent compromised tail gearbox. The red tail rotor… - [NTSB WPR13FA006](https://openairdocs.org/ntsb/WPR13FA006), Oct 7, 2012: Garlick Helicopters UH-1H (N1577), Shady Cove, OR, substantial damage. Probable cause: The separation of the tail rotor gearbox and tail rotor assembly as a result of fatigue to the tail rotor gearbox input quill assembly attachment studs. - [NTSB CEN12LA120](https://openairdocs.org/ntsb/CEN12LA120), Jan 1, 2012: Continental Copters 47G2 (N9021R), Lohn, TX, substantial damage. Probable cause: The improper installation of the tail rotor gearbox by maintenance personnel, which led to accelerated wear of the ring and pinion gears, resulting in the loss of tail rotor effectiveness and… 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.