Radar Altimeter

Radar Altimeter (also called radio altimeter or radalt) is an instrument that measures the aircraft's height above the ground directly beneath it by transmitting radio waves downward and timing their return. Unlike barometric altimeters, it gives true height above terrain regardless of pressure settings.

• Accurate from 0 to approximately 2,500 ft AGL
• Essential for Category II and III precision approaches (provides the Decision Height reference)
• Triggers autopilot callouts: "500", "100", "50", "40", "30", "20", "10" feet during approach
• GPWS/EGPWS uses radar altimeter data as a primary input
• Operating frequency: 4.2–4.4 GHz band