Helinet Aviation Services Agusta A109 S accident
Agusta A109 S · Accident: flight control system malfunction/failure during landing
From Grossmont Hospital Heliport (03CA) to an unrecorded destination
Event
- NTSB case
- WPR21LA039
- 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
- Event fatalities
- Unknown
- 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
- Charter & commuter
- 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
Agusta A109 S
- Aircraft type
- Agusta A109
- 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
- N109EX
- Operator
- Helinet Aviation Services
- Onboard fatalities
- Unknown
- Route
- From Grossmont Hospital Heliport (03CA), La Mesa, CATo not recorded
- Aircraft age
- About 11 years (built 2009)
- 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 135: Air Taxi & Commuter
- 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
- Landing
- 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
- Flight control system malfunction/failure
- 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 from the NTSB case API, which marks them as estimated or does not say; no uncertainty radius is established.
NTSB narrative
The pilot established the helicopter in an approach to land on a rooftop helipad. During the approach, as the helicopter was about 40 ft above the helipad, the helicopter began to yaw to the right despite the pilot’s control inputs. As the pilot continued the approach, he experienced a loss of tail rotor control and attempted to land on the helipad as the helicopter’s right yaw increased. A witness videoed the accident sequence which showed the helicopter rotating clockwise about the vertical axis and rolling to the left before it impacted the helipad. Postaccident examination of the helicopter revealed that the ring nut for the tail rotor duplex bearing was backed out of the sleeve, which resulted in the loss of tail rotor control.
During the investigation, the manufacturer provided historical records of four previous cases that involved ring nut failures. These cases resulted in the manufacturer developing changes to maintenance practices, issuance of European Union Aviation Safety Agency Emergency Airworthiness Directive 2012-0195E in September 2012, and the issuance of Federal Aviation Administration Airworthiness Directive (AD) 2014-02-08, in March 2014, which was superseded by AD 2015-11-08, in June 2015, as a result of a fourth occurrence. The AD added, in part, a daily pilot check to enhance detection of an impending failure of a tail rotor duplex bearing ring nut installation. The accident pilot and the previous pilot who was assigned to the helicopter reported visually inspecting the two locking wires and signing off on the inspection.
Probable cause
The loss of tail rotor control due to the separation of the tail rotor duplex bearing ring nut from the thrust sleeve, which resulted in the loss of helicopter control.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record WPR21LA039
- Event ID
- 20201107102246
- Case number
- WPR21LA039
- 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, coordinates, cause areas. 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: 7f76624b4c54e2da52a436192adc206cbbc41957feb70467302a5f1c63ce3150; retrieved 2026-09-16T13:20:44.808Z.