http://www.baumhedlundlaw.com/aviation2/helicopter.php

This animation shows the cross-sections of the tail rotor yoke. The cross-sections are of reduced thickness to allow for flexure (bending). The yoke is designed to bend within fixed parameters without losing its strength. If a force strikes the tail rotor large enough to bend it beyond its design tolerance, it may result in “static overload” damage, which creates a loss of residual compressive stress and a resulting fatigue fracture. Static overloads occur when the tail rotor is stationary, not when a helicopter is in flight. Static overload can be caused by improper ground handling (such as using the tail rotor blade as a handhold to move the helicopter), collision with a vehicle, improper bearing removal while the yoke is off the helicopter, and wind gust or jet blast. The animation shows the flexure of the yoke 1) within its design tolerance; and 2) outside of its design tolerance.

Baum Hedlund had this animation prepared as one of several to be shown as evidence during the 2006 product liability trial at Los Angeles Superior Court against Bell Helicopter Textron, Inc., and Bell Technical Services, Inc. The trial was conducted by Baum, Hedlund, Aristei & Goldman.

History: A Bell Model 205A-1 helicopter, owned and operated by the LAFD crashed in Griffith Park during an airlift rescue operation in Los Angeles on March 23, 1998. The helicopter was airlifting an injured child from a car accident when the helicopter’s tail rotor yoke failed and caused the aircraft to crash, destroying the helicopter and killing the child, two LAFD paramedics and an LAFD helicopter apparatus operator.

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