MiG-21 modeling discussion.

[+Gepard]

ключ means key, so you can translate включ as switch on or activated

АП – Autopilot

КСИ – (Kurssystem) course system

цд - central damper or smoother, is automatically damping the vibrations of the plane during flight

КАП - (Kursautopilot) course autopilot

I think it are different modes of the autopilot. Some soviet autopilots were able to follow a given course of 3 to 5 waypoints and were able to activate some actions, like weapon release. There is also a "panic system", which brings the plane automaticaly in level flight. This is helpfull if the pilot lost the orientation during flying in fog or clouds. It is said, that it worked very brutal and fast. The central damper or smoother is used when flying in aerodynamic turbulences.