Final answer:
Flight crew members on flight deck duty should have their seat belts and shoulder harnesses fastened during critical phases of flight such as taxiing, takeoff, and landing to ensure safety and prompt response to any incidents.
Step-by-step explanation:
The question asks at which point a flight crew member who is on flight deck duty should remain at their duty station with their seat belt, including their shoulder harness, fastened. While the case study presented does not directly answer this question, it does highlight the importance of movement for passengers to maintain good health during a flight, as demonstrated by Ahaya, the man sitting next to Antônio, moving around to prevent blood clots. In general, flight regulations require crew members, particularly pilots and copilots, to have their seat belts and shoulder harnesses fastened during critical phases of flight, typically including taxiing, takeoff, landing, and any other times as instructed by the pilot-in-command. This ensures their safety and readiness during moments when the likelihood of encountering sudden turbulence or other incidents is higher.