What is the fuel reserve requirement for a turbo-propeller flag air carrier airplane upon arriving at the most distant airport?

The correct answer regarding the fuel reserve requirement for a turbo-propeller flag air carrier airplane upon arriving at the most distant airport incorporates both a contingency plan and compliance with regulatory standards. Specifically, the requirement of "30 minutes plus 15% of total time required or 90 minutes at normal cruise" reflects a comprehensive strategy to ensure sufficient fuel is available for unforeseen circumstances such as delays in landing or diversions to alternate airports.

This approach ensures that aircraft are prepared for variability in flight conditions, allowing for a safety cushion beyond just reaching the destination. The provision of 30 minutes addresses direct fuel needs to manage unexpected holding patterns or other disruptions after arrival, while the additional 15% of total flight time enhances this security by considering potential unplanned increases in travel time. Meanwhile, the alternative of 90 minutes at normal cruise provides a substantial segment of fuel that is more than adequate to accommodate possible delays or emergencies.

In contrast, the other options primarily focus on fixed time frames without incorporating the flexibility of fuel consumption patterns or specific contingency measures needed in aviation operations, which makes them less aligned with established safety practices and operational protocols.