CEN16LA047 · Eurocopter EC120B B
Hanscopter Eurocopter EC120B B · Accident: system/component malfunction/failure (non-power) en route
From Elkhart Municipal Airport (EKM) to Elkhart Municipal Airport (EKM)
Event
- NTSB case
- CEN16LA047
- Event typeAccident: someone killed or seriously injured, or the aircraft substantially damaged (NTSB definition). Incident: an occurrence that affected or could have affected safety, short of that. Glossary
- Accident
- InvestigationHow far the investigation had got when the record was published: preliminary, ongoing, final or completed. Unknown where the source does not say. Glossary
- Completed
- API-reported fatalities
- 0 · all aircraft and ground
- Ground fatalities
- Unknown
- OperationWhat kind of flying it was, grouped by the rules it flew under: airline (US Part 121), air taxi and commuter (Part 135), general aviation (Part 91 and similar), military or government. Glossary
- General aviation
- WeatherVisual meteorological conditions (VMC): good enough to fly by looking outside. Instrument conditions (IMC): cloud or low visibility, flying by instruments. Glossary
- Visual Meteorological Cond
Eurocopter EC120B B
- Aircraft type
- Eurocopter EC120
- Category
- Helicopter
- RegistrationThe aircraft's tail number, such as N12345 or G-ABCD. Registrations are reissued, so the same one years apart can be a different aircraft. Glossary
- N88HA
- Operator
- Hanscopter
- Onboard fatalities
- Unknown
- Route
- From Elkhart Municipal Airport (EKM), Elkhart, INTo Elkhart Municipal Airport (EKM), Elkhart, IN
- Aircraft age
- About 5 years (built 2010)
- Flight rulesThe regulations the flight operated under: in the US, Part 91 (general aviation), Part 121 (airlines), Part 135 (air taxi and commuter) and others; for flights abroad, the NTSB's coarser commercial or non-commercial code. Glossary
- Part 91: General Aviation
- Phase of flightThe stage of the flight when things started to go wrong: standing, taxi, takeoff, initial climb, en route, maneuvering, approach or landing. Glossary
- En route · cruise
- Defining eventThe single coded event the NTSB judges best describes what happened (records from 2008 on). Older records name the first occurrence in the sequence instead. Glossary
- System/component malfunction/failure (non-power)
- DamageDestroyed: beyond practical repair. Substantial: damage that affects the structure, performance or handling and normally needs major repair. Minor: less than that. Glossary
- Substantial
Cause areas
- Aircraft › Aircraft propeller/rotor
Approximate · Coordinates as recorded by the NTSB; no uncertainty radius is established.
NTSB narrative
The flight instructor and helicopter-rated pilot were returning from an instructional flight in the helicopter. The flight instructor reported they heard a noise come from somewhere in the helicopter. They diverted to a nearby airport for a precautionary landing. As they approached the airport, the noise level increased. The instructor took the controls, and, about 15 ft above ground level and 25 knots, the helicopter began an uncommanded left yaw. The instructor responded with corresponding right pedal input; however, it did not stop the left yaw. The instructor immediately reduced engine power and initiated a hovering autorotation.
A postaccident examination revealed the tail rotor drive system's Thomas coupling interface with the main gear box tail rotor output shaft failed. The Thomas coupling was part of the installation of an after-market air conditioning system approved under a supplemental type certificate (STC). Laboratory examinations revealed that while the pulley within the tail rotor drive system was made to the STC holder's requirements, those requirements deviated significantly from the original equipment output flange. Changes were made to the spline profile, manufacturing method, and lubrication regimen. Any of these changes, either independently or collectively, likely contributed to the increased wear and failure of the Thomas coupling. After the accident, the manufacturer issued a service bulletin and the Federal Aviation Administration issued an emergency airworthiness directive that called for an immediate and repetitive inspection of the coupling every 25 flight hours or deactivating the air conditioning system by removing the STC's Thomas coupling and reinstalling the original equipment manufacturer's Thomas coupling half.
Probable cause
The failure of the Thomas coupling at the interface with the main gear box tail rotor output shaft, which resulted in the helicopter's loss of tail rotor control.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record CEN16LA047
- Event ID
- 20151120X64809
- Case number
- CEN16LA047
- Dataset
- full-current
- Source SHA-256
- 5cf380f0061817c0331a6b2d8cc7e0ee3a79bea469a1001dc5c10e56f35f5ab3
Source notes (4)
- Unreviewed is an editorial label, not an investigation status. API-sourced is not report-checked or human-reviewed. Explicit event totals are used without summing aircraft injury tables; onboard allocation is withheld. Unknown values remain unknown. The operation category is mapped from the NTSB-reported FAR part and has not been reviewed.
- Filled from the NTSB case API where the bulk record had no value: investigation status. Values present in the bulk record are kept.
- The date is the local date, which is the same as the UTC date the NTSB stores.
- API snapshot SHA-256: c47cc930ec0ce5c7172cc6c114a86a4ca9acc2043a8699bba36cdcd72d28f46f; retrieved 2026-09-16T02:58:55.229Z.