I have a strange issue with my NAVAID AP-1 wing leveler. While I am on the ground, my head unit will engage with the servo. I can turn on the wing leveler, fast taxi, give hard left & right rudder and I can feel the servo applying oppisite force as well as see the aileron's oppisite deflection. When I am at altitude, I will engage the wing leveler and get no response. It is obvious the servo is not engaging...no pressure is felt on the stick to keep track. The head unit is getting power since the turn coordinator remains lit at all times. Any thoughts to correct this issue would be GREATLY appreciated. Still loving the RV-9A !!!!!!!!!