Terrain following (TF).

A basic guidance mode, providing vertical guidance to maintain an operator selected radar altitude above the terrain. Flight such that the aircraft tries to maintain a constant height above the terrain, usually in the range of 100-1,000 ft; Uses a g-command from the Multi-Mode Radar to generate a flight director cue. This controls the aircraft flight path so that the set clearance altitude is achieved over major high points in the terrain with zero flight path angle. Compare: nap-of-the-earth flight;