所需目视参考(required visual reference): 飞行员应该看到 目视助航设施的一部分或进近区的一部分，并有充分时间让飞行员评 估航空器相对于预定飞行航径的位置和位置变化率。在盘旋进近中， 所需的目视参考是跑道周围的物体。Required visual reference: The pilot should see part of the visual navigation aids or part of the approach area, and have sufficient time for the pilot to evaluate the position and position change rate of the aircraft relative to the predetermined flight path. In circling approach, the required visual references are the objects around the runway.