The system select program pin input sets the system modulation rate and system identification. The modulation rate for the RA 1 system is 145Hz, the RA 2 system is 155Hz.
The aircraft installation delay (AID) program pin is grounded to the 57 feet selection. This calibrates the system so that the radio altitude is 0 feet at touchdown. It makes an allowance for these conditions:
· Length of the antenna cables
· Fuselage to ground distance
· Flare angle.
When grounded, the continuous data program pin selects noninterrupted RA data output at all times.