Which situation does NOT require a preflight check?

A preflight check is an essential part of aviation safety and protocol, ensuring that an aircraft is in optimal condition before any flight operation. The situation that does not require a preflight check is when passengers are entering the aircraft.

This is primarily because the preflight check is intended to assess the aircraft's operational status, safety equipment, and any necessary safety protocols related to flight preparations. Once the aircraft is deemed ready for flight through the proper procedures, boarding passengers does not necessitate an additional check under routine procedures.

The other situations, such as before any scheduled flight, with changes in the aircraft, or before boarding the first flight of the day (FFOD), are critical moments that require thorough inspection to ensure that the aircraft is safe and adheres to all aviation regulations. This helps prevent any issues that could compromise the safety and efficiency of the flight.