after 2 hours I solved this problem on my own. I just put the fps_max and ph_fps_max_lock equal to 50, now almost everything works fine. Yet I have a new question. Every plane has its center of mass where its engine is set, since engine is the heaviest part. But in my plane, the center of mass is just at the center of the plane, so it does not properly fall down, not lke normal planes. I have PH_BOX, so it behaves as if it is a box, how to make the engine understand that the plane's tale is lighter than its engine part? I cannot make it PH_POLY, since it is a moving object.