English: Consider a case of a level sensing platform on an aircraft flying due North with its three gimbal axes mutually perpendicular (i.e., roll, pitch and yaw angles each zero). If the aircraft pitches up 90 degrees, the aircraft and platform's Yaw axis gimbal becomes parallel to the Roll axis gimbal, and changes about yaw can no longer be compensated for (see illustration from outer ring to inner, yaw(magenta) ring is pivoted to pitch(green)ring and pitch(green) ring is pivoted to roll(blue) ring). The word lock is misleading: no gimbal is restrained, all three gimbals can still rotate freely about their respective axis of suspension. Nevertheless, because of the parallel orientation of both the yaw and roll gimbal axes, there is no axis available to accommodate yaw rotation.