Initially when all angles are 0, the aircraft is wings level, nose pointing at the horizon and heading north. Yaw rate is denoted $r$, yaw angle is denoted $\psi$ Pitch rate is denoted $q$, pitch angle is denoted $\theta$ Rotation about the Y-axis is called pitch.
Roll rate is denoted $p$, roll angle is denoted $\phi$ Rotation about the x-axis is called roll.
X-axis is the longitudinal axis pointing out the nose of the aircraft.Roll angle, pitch angle and yaw angle together describe the attitude of an aircraft. Roll, pitch and yaw are rotations about the principle body axis of the aircraft.
