The KNI-415 radar altimeter indicator converts the Analog Altitude from the KRA-405/KRA-405B Receiver-Transmitter to a visible indication of the aircraft altitude. The KNI-415 consists of a fixed dial and servoed motor driven pointer. The servo-mechanism positions the pointer to the correct altitude by balancing the analog altitude and the voltage developed across precision which is positioned by the servoed motor. A Decision Height (DH) annunciator provides the pilot with a visual alarm when the selected decision height is reached. Any time the DH bug is at an altitude lower than the aircraft altitude during descent, the light will come on as the aircraft descends through the DH.The DH lamp may be turned off after it has come on by depressing the lamp once or turned back on by depressing the lamp a second time. The control logic ensures that the DH lamp will light when the aircraft descends through the decision height. The DH lamp is also photocell controlled so that the lamp does not blind the pilot during the critical stage of an approach if low ambient light conditions exist.

The self-test button functionally tests nearly the entire KRA-405 system, and initiates a complete self-test for the KRA-405B. The calibration loop information is transferred to the signal loop for normal processing and displayed as if it were a true altitude. Self-test forces the failure warning systems, including the indicator flag. It also tests the DH if the DH bug is set greater than 50 feet, and provides a 50 foot altitude indication to the pilot. The failure warning indicator to the pilot is a bright red flag which alerts the pilot of possible failures.