What is the procedure for severe turbulence according to the flight protocol?

The procedure for severe turbulence emphasizes the importance of safety and communication within the aircraft. The correct answer highlights that the captain, as the pilot in command, will make an announcement instructing both flight attendants and passengers to sit down and fasten their seatbelts. This is a critical safety measure because it helps to minimize the risk of injury to individuals who might be moving about the cabin during turbulent conditions. The captain's announcement serves not just as a command but also as a means to assure everyone onboard of the necessary steps to take during a potential hazard.

In contrast, other options do not align with established protocol for handling severe turbulence. Serving drinks during turbulence, for instance, poses significant safety risks, as it could lead to spills and injuries. Notifying only the cabin without properly instructing passengers and crew also fails to prioritize safety. While calming passengers is important in a general sense, it does not specifically address the immediate needs for safety during severe turbulence, which requires prompt action to secure everyone onboard.