Final answer:
When the SYS Selector Knob on the ADIRS panel is turned to OFF, the Inertial Reference units (IRs) are not powered and will not operate until power is restored by selecting an operational position.
Step-by-step explanation:
The ADIRS (Air Data Inertial Reference System) panel on an aircraft is used to manage the air data and inertial reference systems which provide critical flight information. If the SYS (System) Selector Knob is rotated to OFF, the Inertial Reference units (IRs) are not powered. The IR units, part of the ADIRS, require electrical power to operate and provide inertial reference data. Turning the SYS Selector to OFF would therefore stop the flow of power to the IR units, making them inoperative until power is restored by setting the SYS Selector to an active position.