Which command should be given upon receipt of the evacuation command?

Upon receipt of the evacuation command, the correct action is to open the door. This is critical for facilitating a swift and safe evacuation of passengers and crew from the aircraft in an emergency situation. Opening the door allows for the immediate release of any built-up pressure and provides a clear exit point, ensuring that everyone can evacuate quickly.

The other options, while relevant in a broader safety context, are not appropriate as immediate responses to an evacuation command. The brace position is essential during an impending impact, but once the command is given to evacuate, the focus shifts to enabling a quick escape. Unstrapping from the jumpseat is necessary for the crew to move but does not directly facilitate the evacuation. Additionally, performing the cabin secure checklist would typically happen before the evacuation command is given and serves primarily to ensure safety measures are in place prior to any emergency procedures.