Radio Altimeter

Source: Airbus

A Radio Altimeter is used to provide an accurate height above ground level when the aircraft is between 0 and 2,500ft. The Radio Altimeter functions by means of radio waves. It transmits radio wave towards the ground and measures the time taken to receive the reflected wave in return. The time between the emission and reception allows the calculation of the height of the aircraft above ground level. The Radio Altimeter system consists of two (three on the A380) independent systems, each system consisting of a transceiver, a transmission antenna and a reception antenna