What is the appropriate action when a whistle is sounded during aircraft movement?

When a whistle is sounded during aircraft movement, the appropriate action is to stop immediately. This signal typically indicates a safety concern or an emergency that requires all personnel to halt their activities to prevent accidents or injuries. Stopping ensures that all personnel have a moment to assess the situation, maintain safety protocols, and allow for any necessary instructions or communications to take place.

Resuming normal operations would ignore the urgency of the whistle signal, potentially leading to dangerous situations. Slowing down may not be sufficient in ensuring that all movement ceases and could still pose risks if the situation requires an immediate and complete halt. Increasing speed is contrary to safety protocol and could further complicate the scenario. Hence, stopping immediately is the most prudent and effective response to a whistle during aircraft operations.