Ventilation Control Panel
Blower Fan Switch
AUTO - When both avionic equipment blower and extract vent fan switches are in AUTO the avionics equipment ventilation system is configured for the normal operational configuration.
OVRD - When the avionics equipment blower vent fan switch is selected to OVRD (override), this action turns the blower fan off and both the vent air inlet and outlet valves will close, configuring the avionics equipment ventilation system to the abnormal configuration if the extract switch is in AUTO. When both blower and extract vent fans are in OVRD, then the ventilation system changes to the smoke configuration.