During a time available-short notice emergency, what command should you shout 30 seconds before landing?

The command "Brace, Brace" is critical during emergencies as it prepares passengers for a sudden impact upon landing. This command is universally recognized and prompts immediate action. By repeating the word "Brace," it reinforces the urgency and seriousness of the situation, ensuring that all passengers understand that they must take protective measures. This can include positioning themselves to minimize injury during impact.

The other options are not as effective in conveying the immediate need for passengers to adopt a protective stance. "Stay seated, brace up," while clear, could create confusion due to its less direct command. "Prepare for landing" doesn't explicitly instruct passengers on how to position themselves, and "Hold onto your seats" may not adequately prepare them for the intense impact they may face. Thus, the clarity and urgency of "Brace, Brace" make it the appropriate choice in such scenarios.