[Peetwo]

NTSB release FR into LA Augusta chopper prang - 

Very graphic video footage, courtesy Aviation Accidents/This day in history, via Youtube:

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and the issuance of Federal Aviation Administration Airworthiness Directive (AD) 2014-02-08, in March 2014, which was superseded by AD 2015-11-08, in June 2015, as a result of a fourth occurrence.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.

Very lucky the chopper came to rest on the rooftop helipad, literally centimetres from falling off the edge of the building...coming to a vertiport near you??  

MTF...P2