The Bell 205A-1 tail rotor yoke is heat treated, forged 15-5 PH (precipitation hardened) stainless steel with an ultimate tensile strength of 170-200 KSI. The yoke has cross-sections of reduced thickness to allow for flexure, and cadmium plating for corrosion resistance.

After the yoke in this case was machined, it underwent a process called "shot peening." This animation depicts the shot peening process - tiny beads are blasted onto the yoke. This process induces residual compressive stresses that impart greater fatigue strength to the yoke. One of the issues in the case was whether this Bell 205A-1 tail rotor yoke had been subjected to shot peening that did not conform to Bell Helicopter Process Specification (BPS) 4409. Inadequate shot peening reduces the residual compressive stress and fatigue strength of the yoke.

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 lead trial counsel Ronald L. M. Goldman and J. Clark Aristei of 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.

View Other Bell Helicopter Crash Animations

Tail Rotor Loss	Yoke Breakdown	Flexure Loss	Cracking Yoke

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