Pilot Noticed A Slight Yaw To The Right That Continued Despite Full Left Pedal Application
Location: Los Angeles, CA Accident Number: WPR21LA039
Date & Time: November 6, 2020, 15:00 Local Registration: N109EX
Aircraft: Agusta A109 Injuries: 1 Minor, 2 None
Flight Conducted Under: Part 135: Air taxi & commuter – Non-scheduled
On November 6, 2020, about 1500 Pacific daylight time, an Agusta A109S helicopter, N109EX, was substantially damaged when it was involved in an accident at the University of Southern California (USC) Keck Medical Center (USC Keck), Los Angeles, California. The pilot sustained minor injuries, and the two passengers were uninjured. The helicopter was operated as a Title 14 Code of Federal Regulations Part 135 Helicopter air ambulance flight.
The pilot reported that he established the helicopter in a steep approach, to land on the rooftop helipad of a multi-story medical building. The pilot had offset his heading to the left to gain greater visibility to the landing zone. He observed the absence of any wind indication from the windsock and no movement on nearby trees. When the helicopter had decelerated to about 45 knots, he increased the engine and rotor RPM to 102%. About 40 feet above the helipad, the pilot noticed a slight yaw to the right that continued despite full left pedal application. He thought to fly away from the helipad when the helicopter aligned in the direction he just approached from. As the helicopter rotated to about 90° from his approach heading, it suddenly and very violently made a dramatic increase in right yaw. Realizing the helicopter was going to be uncontrollable, the pilot “dumped the collective” and tried to stay over the helipad. He stated that after the helicopter struck the helipad, it rolled left and continued spinning on its side, and eventually came to a stop. The pilot performed an emergency shut down of the engines and exited the helicopter unassisted. The passengers exited unassisted.
A review of a witness video, taken from an adjacent building, revealed the helicopter approached the rooftop helipad while slowly rotating clockwise about the vertical axis. The helicopter stopped descending and rotated 360°. The helicopter then descended while rotating an additional 180° and rolled to the left before impacting the helipad. The main rotor blades contacted the helipad, followed by the left main landing gear and the fuselage. The helicopter descended out of view of the camera.
The helicopter came to rest on its left side, on the helipad. The four composite blades of the main rotor system fragmented and separated, spreading debris throughout the rooftop and down to the ground. The tail rotor and 90° gearbox separated and were found on the rooftop. The left main landing gear separated and remained near the attachment points of the fuselage.