What is used to keep the plane at a constant attitude?

Keeping a plane at a constant attitude relies primarily on the control surfaces, such as the ailerons, elevators, and rudder. These surfaces are crucial for managing the aircraft's orientation in the air. The control surfaces adjust the aircraft's pitch, roll, and yaw, allowing the pilot to maintain the desired attitude during flight. By manipulating these surfaces, pilots can counteract any deviations from the intended attitude caused by external factors like turbulence or changes in airspeed.

While power settings can influence altitude and airspeed, they do not directly control the aircraft's pitch or angle of flight. Flight management systems assist with navigation, route planning, and optimizing performance but do not directly influence attitude control. Altitude indicators provide information on the aircraft's height above sea level but do not serve as a tool for maintaining orientation. Thus, the control surfaces are the primary means by which pilots maintain a constant attitude.