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Avionics Ventilation System
The avionics ventilation system provides cooling air for the avionics compartment and flight deck instruments. Air is recirculated from the cabin, passes through a ground cooling unit in the case of extremely hot air, and is provided to the avionics equipment before being extracted by an extraction fan. On the ground, with the engines not running:
- air extracted from the avionics equipment is discharged overboard through an OVBD valve
- the ground cooling unit operates when the air in the avionics compartment is too hot, drawing air through a fan and rejecting it overboard through the ground cooling valve
Otherwise:
- air from the avionics equipment is blown through the INBD valve, under the forward cargo compartment, and overboard through the forward outflow valve
The INBD and OVBD valves operate in the opposite sense to each other. With the OVBD valve open, the aircraft will not pressurise due to its size, although it can be partially opened in flight.
The GND COOL indication on the CAB PRESS page provides information on the state of the ground cooling system. The VENT EXTRACT indication represents the overboard valve. On the ground they are normally open, inflight they are closed.
Avionics equipment ventilation controller
The AEVC controls the avionics ventilation system and sends opening and closing signals to the overboard, inboard, and ground cooling valves.
The AEVC also controls a turbofan which ventilates the pack bay area.
Cooling effect detector
The CED triggers an ECAM caution when the cooling capacity (flow and temperature) of the blown air is abnormal.
Failures
| PACK BAY VENT FAULT | - pack bay ventilation turbofan has stopped working - a ground horn sounds after 5 minutes - the pack may still be available in flight using ram air for cooling |
| VENT OVBD VALVE FAULT | - the EXTRACT pb sw must be set to OVRD - if this is unsuccessful inflight, the outflow valves must be closed manually |