21-30 Ventilation Flashcards
Ventilation is provided for?
1) Avionics
2) Batteries
3) lavatories and galleys
4) cargo ventilation (if the aircraft has it)
What are the three configurations of the avionics ventilation system?
1) open circuit
2) closed circuit
3) intermediate
What is open circuit configuration?
Air enters via the skin air inlet valve, it is drawn by the blower fan. Its passes over the avionics equipment, extracted by the extractor fan and overboard through the skin air outlet valve.
When is the ventilation system in the open circuit configuration?
1) The A/c is on the ground
+
2) throttle is not set to TO thrust
+
3) Skin temperature is greater than on the ground threshold
What is the on ground temperature threshold that the skin needs to be above to go into open configuration?
+12 degrees and increasing
Or \+9 degrees and decreasing
What is the closed circuit configuration?
The skin air inlet and outlet valves are closed and the avionics air is cooled by the skin heat exchanger. The skin exchange isolation valve and the skin exchanger inlet and outlet bypass valves open to enable air to circulate between the avionics bay and the space under the cargo compartment floor.
When does the aircraft go into the closed circuit configuration on the ground?
1) before TO thrust is set
+
2) skin temperature is below:
\+ 12 degrees increasing
\+ 9 degrees decreasing
OR
1) thrust levers are set to take off power
\+
2) skin temperature is below:
\+ 35 degrees increasing
\+ 32 degrees decreasing
When does the aircraft go into closed circuit configuration in the air?
skin temperature is below:
\+ 35 degrees increasing
\+ 32 degrees decreasing
What are the skin exchange bypass valves used for?
If the AEVC (avionics equipment ventilation computer) detects airflow greater than required part of the hot air is ducted below the floor of the forward cargo compartment and the avionics bay
What is the intermediary configuration?
It is like the closed circuit except due to high skin temperature some of the air is extracted through a small flap in the skin air extract valve.
When does the aircraft go into the intermediary configuration?
1) in flight
\+
2) skin temperature is above:
\+35 degrees and increasing
OR
\+ 32 degrees and decreasing
What happens when you press OVRD during a blower fan fault?
The system operates in the closed circuit configuration and and the blower fan stops. Air conditioned air is passed through the air conditioning inlet valve.
What happens then the OVRD button is pressed when you have an extract fan fault?
Both fans run but the AEVC no longer controls the extract fan. Air conditioning air is added to the system and it operates in the closed circuit configuration.
What happens when the smoke detector detects smoke in the avionics bay and you select the Blower and extract fan to override?
The air conditioning system supplies cooling air, the blower fan stops. The extract fan continues to run, all valves close except the small flap in the skin air extract valve.
What happens when both controllers fail?
Air conditioned air is added.
The blower stops, the skin exchange inlet bypass valve closes, the small skin air inlet flap opens.
The skin air inlet valve, skin exchange isolation valve and the outlet bypass valve remain in the last position checked before the failure occurred.
See graphic
