What is the angle between the longitudinal axis and the horizon?

The correct answer, pitch attitude, refers specifically to the angular relationship between the aircraft's longitudinal axis and the horizon. This angle is crucial in determining how the aircraft is oriented in space relative to the ground.

When the aircraft is climbing, descending, or maintaining level flight, the pitch attitude will change accordingly. Measuring pitch attitude helps pilots understand how the nose of the aircraft is oriented with respect to the Earth's horizon, which is essential for effective flight control and navigation.

In contrast, the angle of attack measures the angle between the chord line of the wing and the relative wind, which is different from how the aircraft is positioned relative to the ground. The angle of incidence denotes the fixed angle between the wing and the aircraft's longitudinal axis in its static configuration, not the dynamic pitch attitude during flight. Groundspeed refers to the speed of the aircraft relative to the ground and does not concern attitude at all.

Understanding pitch attitude is vital for pilots as it directly influences the aircraft's lift and drag characteristics, which in turn affects performance during various flight maneuvers.