The Air Data and Attitude and Heading Reference System (ADAHRS) performs attitude, heading, and vertical acceleration calculations for the AXIS™ System, utilizing GPS, magnetometer, and air data in addition to information from its internal sensors. Attitude and heading information are updated on the PFD while the AHRS receives appropriate combinations of information from the external sensor inputs.

The ADAHRS (GSU) corrects for shifts and variations in the Earth’s magnetic field by applying the Magnetic Field Variation Database. The Magnetic Field Variation Database is derived from the International Geomagnetic Reference Field (IGRF). The IGRF is a mathematical model that describes the Earth’s main magnetic field and its annual rate of change. The database is updated approximately every 5 years. Failure to update this database could lead to erroneous heading information being displayed to the pilot.

Loss of GPS, magnetometer, or air data inputs is communicated to the pilot by message advisory alerts. Any failure of the internal ADAHRS inertial sensors results in loss of attitude and heading information (indicated by red ‘X’ flags over the corresponding flight instruments). If the AXIS flight display senses that the magnetic heading measurement is valid, but possibly outside of the internal accuracy limits, the numeric heading value on the PFD is displayed in yellow.

If GPS input fails, the ADAHRS can continue to provide attitude and heading information to the PFD as long as magnetometer and airspeed data are available and valid.

If the magnetometer input fails, the ADAHRS continues to output valid attitude information; however, the heading output on the PFD Page is flagged as invalid with a red ‘X’.

Failure of the air data input has no effect on the ADAHRS output while ADAHRS is receiving valid GPS information. Invalid/unavailable airspeed data in addition to GPS failure results in loss of all attitude and heading information. Likewise, loss of magnetometer (heading) data, in combination with loss of GPS data results in a loss of all attitude and heading information.

In installations that include multiple AHRS units (AXIS supports up to three AHRS sources) if data from an AHRS source is lost the AXIS will automatically switch sources, when a failure is detected. Reversionary sensor selection is annunciated in a window on the right side of the PFD. These annunciations reflect reversionary sensors selected on the PFD. The GPS sensor cannot be switched manually.

If a standby flight display (such as a Garmin G5 Electronic Flight Instrument) is installed, it will also provide a redundant source of attitude and air data in addition to that provided by the dedicated ADAHRS unit. If the sensor source selection is AUTO and attitude or air data is unavailable from any dedicated ADAHRS unit, the PFD will automatically revert to displaying data from the standby display. This will be annunciated on the PFD with an 'ON AHRS (#)' or 'ON ADC (#)' or 'ON SFD (#)' or 'ON SFD (#) ADC' message.