Which unit is primarily used for determining aircraft attitude and heading?

The primary unit used for determining aircraft attitude and heading is the Attitude Heading Reference Unit (AHRU). This unit combines both attitude and heading information, providing pilots with essential data regarding the aircraft's orientation in three-dimensional space relative to the Earth's surface. It utilizes various sensors and data inputs, such as gyroscopes and accelerometers, to maintain accurate readings, even in various flight conditions.

The AHRU is vital for navigation and helps pilots maintain control, especially during maneuvers that require precise spatial awareness. By processing information from its sensors, it can provide real-time updates on the aircraft's lateral and vertical positioning, ensuring that pilots have the necessary information to make informed decisions during flight.

Other options like Gyro Stabilization Units and Heading Direction Indicators may contribute to heading data but do not provide the comprehensive attitude information that the AHRU does. Altitude Reference Units, while critical for altitude data, are not involved in determining aircraft orientation or heading. Thus, the AHRU stands out as the essential system for this function in aviation navigation.