Definition

An Attitude and Heading Reference System (AHRS) provides the same information as traditional mechanical gyros that are found in attitude indicators and heading indicators. However, an AHRS provides more accurate data through the use of electromechanical gyros, accelerometers, and a magnetometer or flux valve.

Description

An AHRS system, like traditional gyroscopic instruments, senses roll, pitch, and yaw. Solid-state components react to changes as the aircraft maneuvers, and input from the components is aggregated to produce accurate attitude and heading readings. AHRS equipment originally appeared mainly in commercial and military aircraft. However, as the technology has matured and become less expensive, it has become more common in general aviation (GA) aircraft.

Unlike traditional gyroscopic instruments, AHRS-driven instruments are not subject to precession error and do not require periodic manual adjustments. In addition to the primary role of supporting flight instrumentation, AHRS systems can also send data to autopilots and flight directors as well as yaw dampers, flight data recorders, and other components.

On startup, AHRS systems automatically conduct an alignment as the unit determines the initial attitude of the aircraft. Depending on the AHRS model, this can take anywhere from a few seconds to a few minutes. It is important not to move the aircraft during AHRS alignment. Moving the aircraft during this time can induce errors that are not readily apparent on the ground, but may become more pronounced in flight. Most AHRS units also allow for an in-flight alignment in the event of power loss or other malfunction.

In the event of complete AHRS failure, pilots can revert to traditional standby flight instruments.