AUTO FLIGHT Switch:
Engages ATS and one AP in the FD mode that has been selected. If no FD mode has been selected, the AP engages in HDG/TRK HOLD and either altitude hold (if level) or vertical speed hold (if climbing/descending). After AP engagement, each push alternates the AP between AP1 and AP2. This is displayed on the FMA

Flight manual:
https://www.captainsim.org/forum/csf.pl?num=1704810430/0#0

On the ground before takeoff press the AUTOFLIGHT button, and if the throttle levers are moved to a position greater than 40%, A/T will be activated and the takeoff will begin. After takeoff you must press the AUTOFLIGHT button again and the heading mode will turn on. If you need to maintain the flightplan, you need to press the NAV button.