Under what circumstance can train crew members be near the top of MU equipment?

When crew members are near the top of MU (Multiple Unit) equipment, it is a specific action that usually requires careful consideration of safety protocols. Being authorized by supervision for grounding the equipment is the correct circumstance because it involves a specific task that needs to be completed, which often requires crew members to safely access the top of the train. This action is generally performed to ensure that the equipment is properly grounded to prevent electrical hazards while maintenance or troubleshooting is conducted.

Grounding the equipment is a critical safety measure that ensures the crew can work without the risk of electrocution from the electrical systems on board. Under normal operations and even during emergencies, crew members are typically not allowed on the tops of trains unless they have been specifically authorized for tasks like grounding. The context of supervision authorization emphasizes the importance of a safety-first approach and the need for training and protocols to minimize risks associated with working in difficult or potentially dangerous areas.