What is the best indicator to the pilot of the load factor of the airplane?

The load factor of an aircraft refers to the amount of stress or g-forces acting on it during various maneuvers. It is influenced by the aircraft's speed, altitude, and the types of maneuvers being performed. The best indicator for the pilot regarding the load factor is how firmly the pilot is pressed into the seat during a maneuver.

When the aircraft experiences changes in speed or direction, the load factor increases, causing a sensation of being pushed into the seat. This feeling directly correlates with the g-forces acting on the aircraft and the pilot. As the load factor increases, the pilot will experience greater pressure against the seat, helping them to understand the current aerodynamic forces truly affecting the aircraft.

The other options provide important information but do not directly reflect the load factor as experienced by the pilot. For instance, altitude and the attitude of the aircraft are important for situational awareness, and the airspeed indicator can offer some context regarding performance but does not provide a direct measure of how the aircraft's acceleration affects the pilot's physical state. Thus, the pilot's physical sensation of pressure in the seat serves as the most effective and immediate gauge of the load factor during flight maneuvers.