Brief Description: ARINC Output From EFIS to Autopilot - Part 1
Today I added the ARINC differential serial output from the EFIS system to the Autopilot to provide Lateral and Vertical steering for the Autopilot system. This data is significantly better than just the standard GPS NEMA 0183 feed for a variety of reasons (although the GPS has this data feed to as a backup). Note that the "low" speed ARINC mode must be selected on the GRT EFIS to correctly couple to the TruTrak Autopilot.
Basic directional control to the Autopilot (NAV Mode) is provided by digital selection of a GPS track to be flown from the standard NEMA 0183 data link.
In the GPS NAV mode of operation (via the ARINC differential serial data link) the system responds to Digital Flight Plan Guidance information so as to fly a complex navigation program. This function is referred to as GPS Steering (GPSS mode).
The vertical portion of the system contains a digital altimeter and associated altitude selector capable of selection in increments as small as fifty feet. Altitude transitions can be made either by airspeed or vertical speed selection. If an upward vertical speed is selected which is beyond the capability of the aircraft, there will be no stall. Instead, the Autopilot will cause the aircraft to climb at a pre-set minimum safe airspeed.
When and ILS approach is initiated and the CDI becomes active, the GPSV button on the Autopilot can be pushed and the unit will enter the GPSV mode (GPS Vertical Steering). As the VDI passes through center, the Autopilot will couple to the virtual glide slope, and the display will show that the Autopilot is now coupled to the virtual glide slope and fly the ILS approach.
