Special consideration need to be taken for radio altimeter systems utilizing 2 antennas. Radio altimeter antennas such as the Bendix/King KA-54A, Collins ANT-52, or Sensor Systems S67-2002 series should be mounted with the following conditions met:

• Pointing straight down plus or minus 6 degrees when the aircraft is in level flight
• Mount in-line or side-by-side although in-line is preferred
• Angle between the antenna centerlines should be less than 6 degrees
• Mount no less than 20 inches apart
• Mount at a distance not greater than the height above terrain at touchdown
• Mount closer than the antenna height above terrain
• Location should provide 120 degree clearance cone
• Surface area should be free from seams or other discontinuities

Failure to meet any of these installation considerations could result in the following system performance discrepancies:

• Erratic operation on the ground
• Needle fluctuation as much as 20 feet
• Pointer may not stow above 2500 feet
• Terrain area may not be illuminated for ground level operation
• System could lock on to a single altitude
• Loss in system sensitivity
• "Peeking" could occur in which pointer comes into view above 2500 feet AGL