An operator of a crane should NOT rely on the boom angle indicator for radius accuracy when lifts exceed what percentage of the rated capacity?

The reasoning behind not relying on the boom angle indicator for radius accuracy when lifts exceed 75 percent of the rated capacity centers on safety and the potential for miscalculation. Boom angle indicators provide a general reference for the positioning of the boom but can be subject to inaccuracies, especially under heavy load conditions. As the load approaches the rated capacity, the stresses and dynamics involved in the lift become more complex, and relying solely on the boom angle could lead to unsafe operations if the actual load radius is not accurately assessed.

At 75 percent or more of the crane's rated capacity, operators should use more precise methods to determine the load radius, such as using load charts and taking direct measurements. This mitigates the risks associated with overload situations that could lead to equipment failure or accidents. In heavy lift scenarios, it is crucial to employ the most accurate tools available to ensure safety and operational efficiency.