Are you talking about a turn coordinator? That doesn't show "down." The sum of forces acting in a coordinated turn will keep the ball centered even though the a

Are you talking about a turn coordinator? That doesn't show "down." The sum of forces acting in a coordinated turn will keep the ball centered even though the airplane is banked. Also I'm not sure what you're talking about with using the real horizon as a backup to the artificial horizon. It's not meant to be a redundant setup. Artificial horizons aren't required for visual (looking outside) flight, and relying primarily on the instruments in visual flight is an error. In clouds/poor visibility, the cross-check for the artificial horizon is provided by the other flight instruments: airspeed, altimeter, turn coordinator, vertical speed indicator, and directional gyro (or their equivalents on an electronic display).