Loss of control Accident Agusta A109S Grand N109EX,
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ASN Wikibase Occurrence # 244696
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Date:Friday 6 November 2020
Type:Silhouette image of generic A109 model; specific model in this crash may look slightly different    
Agusta A109S Grand
Owner/operator:Helinet Aviation Services / Prime Healthcare
Registration: N109EX
MSN: 22145
Year of manufacture:2009
Total airframe hrs:1446 hours
Engine model:Pratt & Whitney PW207C
Fatalities:Fatalities: 0 / Occupants: 3
Aircraft damage: Substantial
Location:USC Medical Center Heliport (35CA), Los Angeles, CA -   United States of America
Phase: Landing
Departure airport:Sharp Grossmont Hospital Heliport, CA (03CA)
Destination airport:Los Angeles Co/USC Medical Center Heliport, CA (35CA)
Investigating agency: NTSB
Confidence Rating: Accident investigation report completed and information captured
On November 6, 2020, about 1500 Pacific daylight time, an Agusta (Leonardo) A109S helicopter, N109EX, was substantially damaged when it was involved in an accident at the University of Southern California, Keck Medical Center, Los Angeles, California. The pilot and one passenger sustained serious injuries, and one passenger were uninjured. The helicopter was operated as a Title 14 Code of Federal Regulations Part 135 helicopter air ambulance flight.

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.

Accident investigation:
Investigating agency: NTSB
Report number: WPR21LA039
Status: Investigation completed
Duration: 2 years and 2 months
Download report: Final report




https://www.airport-data.com/images/aircraft/000/554/554429.jpg (photo)



Photos: NTSB

Revision history:

07-Nov-2020 03:42 Captain Adam Added
07-Nov-2020 06:17 RobertMB Updated [Time, Aircraft type, Registration, Cn, Operator, Location, Destination airport, Source, Narrative]
07-Nov-2020 07:33 Geno Updated [Time, Location, Departure airport, Destination airport, Source, Narrative]
07-Nov-2020 08:51 Aerossurance Updated [Narrative]
07-Nov-2020 08:57 Aerossurance Updated [Narrative]
07-Nov-2020 09:04 Aerossurance Updated [Source]
07-Nov-2020 09:36 Aerossurance Updated [Embed code]
07-Nov-2020 13:58 RobertMB Updated [Embed code, Narrative]
07-Nov-2020 14:08 Aerossurance Updated [Source]
07-Nov-2020 16:37 harro Updated [Source, Category]
08-Nov-2020 18:54 Aerossurance Updated [Embed code]
09-Nov-2020 15:07 Aerossurance Updated [Operator, Departure airport, Source, Narrative]
16-Nov-2020 16:10 Geno Updated [Departure airport]
08-Dec-2020 13:39 Aerossurance Updated [Source, Embed code]
27-Feb-2021 18:51 rudy Updated [Embed code, Category]
07-May-2021 14:12 harro Updated [[Embed code, Category]]
25-Jul-2023 20:23 harro Updated [[[Embed code, Category]]]

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