The KRA-405B (RADALT) is a lightweight, solid-state, airborne altimeter that measures the absolute height of the aircraft above the terrain, this is accomplished by transmitting a signal to the ground and processing the received signal into a period proportional to range.   The transmitted signal is a Frequency-Modulated Continuous-Wave  (FMCW). By the time the transmitted signal has been reflected from the terrain and back to the receiving antenna, the transmitter has shifted to a new frequency.

The KRA-405B system consists of the KRA-405B receiver/transmitter, the KNI-415 or KNI 416 indicator, and two KA-54A antennas. The KRA-405B is a remote mounted receiver/transmitter. The KRA-405B can be rigid, tray or shock mounted. The radar altimeter system provides the pilot a precise 0-2000 feet AGL information. The KRA-405B unit contains 3 PC boards. The KRA-405B provides 3 discrete outputs called Altitude Trip Point #1, Altitude Trip Point #2, and Altitude Trip Point #3. The KRA-405B asserts the discrete output when operating at an altitude below the configured trip point. The factory settings are: Altitude Trip Point #1 at 200 feet, Altitude Trip Point #2 at 500 feet, and Altitude Trip Point #3 at 1200 feet. If any other altitude is desired, a programmed configuration module must be installed with the KRA-405B. 10,000 KRA-405Bs have been produced and sold to date with more than four million service hours, the KRA-405B (RADALT) has proven to be one of the most reliable and industry proven radar altimeters available.