When the IR mode selectors on the ADIRS panel are in the ATT position, they provide attitude and heading information using internal gyroscopes and accelerometers, even without external data.
The ADIRS (Air Data Inertial Reference System) panel, when set with the IR mode rotary selectors in the ATT (attitude) position, supplies attitude and heading information to the aircraft's systems.
This mode is typically used when the aircraft's air data is unreliable or not necessary, such as when on ground prior to takeoff.
The ADIRS utilizes gyroscopes and accelerometers in this mode to provide an accurate representation of the aircraft's orientation relative to the earth's horizon, independent of external references.