What is the proper uniform for ground crew members conducting sling load operations?

For ground crew members conducting sling load operations, the appropriate uniform is Kevlar with the chinstrap fastened. This choice is correct because the use of a Kevlar helmet is critical for safety during these operations. Sling load operations can involve significant risks, including the potential for falling objects and rotor wash, which can create hazardous conditions. The chinstrap helps to ensure that the helmet remains securely in place, offering protection to the individual in case of sudden movements or when operating in close proximity to aircraft.

The other options do not provide adequate protection for the ground crew. Casual clothing would offer no protection at all, and shorts and a T-shirt would leave the crew vulnerable to injuries. Parkas may provide warmth but would not provide the necessary protective features needed in such an operational context. The proper gear is essential for ensuring personnel safety and maintaining situational awareness during the complex and potentially dangerous scenarios presented during sling load operations.