When can additional shots or weight be added to the standard configuration of an E-5 barrier?

The correct answer highlights that additional shots or weight can be added to the standard configuration of an E-5 barrier when the aircraft weighs over 20,000 pounds. This guideline is established to ensure proper safety measures and effectiveness of the barrier system in restraining aircraft during emergencies. As aircraft weight increases, the dynamics involved during an arrestment also change, necessitating enhanced barrier capabilities.

In the context of safety and operational efficiency, the standard configuration of the barrier is designed to accommodate typical aircraft weights, but it has thresholds beyond which modifications become essential. By allowing adjustments for aircraft exceeding 20,000 pounds, the guidance optimizes performance and minimizes the risk of failure during critical operations.

The other weight thresholds provided in the options indicate higher increments, which are not aligned with the established safety protocols for barrier modifications. This 20,000-pound threshold is a critical point that balances the need for increased barrier strength with operational realism, ensuring that modifications are made in a timely manner to adequately protect both the aircraft and ground personnel.