The radio altimeter (RA) system supplies the pilots and airplane systems with altitude above the terrain. The system operates at low altitude (0 to 2,500 feet).
The system has three transceivers each with its own transmit and receive antennas. The transceivers
calculate the radio altitude, which shows on the primary flight display (PFD).
Each pilot can select a radio minimums altitude on the onside EFIS control panel. The radio minimums show on the onside PFD above the radio altitude display.
When the radio altitude is equal to or less than the radio minimums, the radio minimums display and the radio altitude change color and momentarily flash.
The RA system also supplies radio altitude data to these units:
• Autopilot flight director computers (AFDCs)
• Ground proximity warning computer (GPWC)
• Traffic alert and collision avoidance (TCAS) computer.
The central maintenance computer function (CMCF) of AIMS does a test of the RA system.