- A special radar that permits aircraft to be flown safely at a preset clearance level. A normal PPI (plan position indicator) radar enables the terrain to be avoided in azimuth rather than in elevation. A specialist terrain avoidance radar, on the other hand, only displays terrain that penetrates above a preset clearance level.The target spot represents the path with the aircraft should be following to clear the ground ahead by the required amount and the aiming mark is its present path. These representations are enlargements of head-up displays.
Aviation dictionary. 2014.
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