What computers control operation of the bleed air system?
The BACs are installed on the aft side of the baggage compartment bulkhead. The units are digital, microprocessor-based and are designed to automatically regulate bleed air manifold supply pressure and temperature. They are capable of controlling bleed air for all systems utilizing bleed air within the capacity of the engine over the entire aircraft operating envelope.
One function of the bleed air system is temperature regulation. To avoid high temperatures inside the aircraft, fan air is used as a cooling medium together with a bleed air precooler located in each pylon.
There are only three sources of air on ground.
External, APU and engine air. Airflow is supplied to aircraft systems through a bleed air manifold connected to both engines and the APU. The manifold also has a connection to allow an external cart to provide pressurized air for engine starting or air conditioning on the ground.
As long as the engine is operating, bleed air is always available for the TAI system, even when the respective bleed air system is selected OFF.
What are the aircraft systems that require a modulated pneumatic source?
What are the requirements for APU load control valve to open in-flight?
When the APU is running and APU bleed air pressure is higher than engine bleed air pressure, the APU check valve opens to allow _____. When engine bleed air pressure exceeds APU bleed air pressure, the APU check valve closes, preventing the reverse flow of air into the APU.
When the L ENG or R ENG switch (BLEED AIR panel, COP) is selected 'ON', the PRSOV opens and allows HP 8 bleed air to flow to the respective side ECS and to the air starter ducting. The Pressure Regulating and Shutoff Valves (PRSOV) controls the supply of bleed air to the Environmental Control System (ECS) from the engine.
When the L ENG or R ENG switch (BLEED AIR panel, COP) is selected 'ON', the PRSOV opens and allows HP 5 bleed air to flow to the respective side ECS and to the air starter ducting. When ECS system demand is greater than HP 5 supply, the HPSOV opens, allowing HP 8 air to supplement the bleed air system. The HPSOV is regulated by a sense line downstream of the servo pressure regulator / torque motor.
The APU can be operated on the ground, during takeoff, in flight and during landing. In flight it is an optional source of electrical power via the APU GEN instead of one or both engine-driven generators. The APU cannot be used to supply pressurization airflow in flight. The APU may be used for starter assisted main engine starts at and below _____ if required.
Air supplied by the APU or a ground cart is not regulated.
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