When should a helicopter pilot consider using a running takeoff?

A helicopter pilot should consider using a running takeoff when gross weight or density altitude prevents a sustained hover because these factors directly impact the aircraft's performance capabilities. In situations where the helicopter is operating near its maximum gross weight or in a high-density altitude environment, the available lift is reduced, making it difficult to achieve and maintain a hover.

In such cases, a running takeoff allows the helicopter to transition to forward flight while gaining lift gradually, rather than relying solely on the vertical lift capacity. This method takes advantage of the rotor system's efficiency at forward speed and can help the aircraft clear obstacles more safely and effectively.

While the other options may present scenarios relevant to helicopter operations, they do not encapsulate the critical relationship between gross weight, density altitude, and the limitations these pose regarding hovering, which makes using a running takeoff the appropriate decision in those circumstances.