18 Questions
What happens when the ISOLATION switch is selected to 'ON'?
It allows the bleed air isolation valve to open, permitting a crossflow of bleed air between the left and right systems.
What are the three sources that supply air to the pneumatic system?
Compressor section of the left and right engines, Auxiliary Power Unit (APU) bleed air, external air cart
How is the temperature and pressure of the air supplied by the engines regulated?
By Bleed Air Controllers (BACs) that monitor the air supply via sensors within the ductwork
What is used to regulate the temperature of the supply air and which stage of the compressor sections do the BACs draw air from?
Precooler heat exchanger; 5th (mid-stage) or 8th (high stage) of the compressor sections of the engines
How can the BAC be reset during flight if multiple BAC processor corrections are required?
By cycling electrical power to the BAC off and on
What happens when the BLEED AIR CTL CMD is selected to ON?
When selected to ON, essential 28V DC bus power is provided to the associated system, and the associated Bleed Air Controller performs a BIT check and establishes operational parameters.
What is the function of the APU bleed air primarily used for?
Air conditioning and engine starting on the ground
How is the crossflow of bleed air between the left and right systems achieved when one side of the ECS system is inoperative?
By selecting the ISOLATION switch to 'ON'
Which systems are supplied with modulated pneumatic source from the pneumatic system?
Air conditioning and pressurization, Pressurization safety valve, Wing anti-ice, Engine starting, Aircraft water system, Total Air Temperature (TAT) probe airflow (ground only)
From which compressor stages do the Bleed Air Controllers (BACs) draw air for regulating the temperature and pressure of the air supplied by the engines?
5th (mid-stage) or the higher temperature 8th (high stage) of the compressor sections of the engines
How is the temperature of the air regulated for the supply air from the engines?
By selective switching between compressor stages for a source of supply air and by passing the supply air through a precooler heat exchanger that uses ambient air drawn into the engine at the fan intake stage of the compressor
What is the purpose of the fan air valve in the bleed air system?
To control the amount of fan air through the precooler to limit the temperature of the air in the bleed air manifold.
What is the power source for the left and right Bleed Air Controllers (BACs), and how are they reset during flight?
The left BAC is co-powered by 28V DC from the left Essential DC bus through circuit breakers, and the right BAC is co-powered by 28V DC from the right Essential DC bus through circuit breakers. The BACs can be reset by cycling electrical power to the BAC off and on.
How is the temperature of the supply air regulated during wing anti-ice on modes?
The high-stage provides temperature augmentation by mixing the high-stage air with mid-stage air and changes the temperature control set point at the precooler inlet to 630°F (332°C).
What is the purpose of the APU bleed air in relation to engine bleed air?
The purpose of the APU bleed air is to be inhibited when sufficient engine bleed air is available.
What is the effect of selecting the BLEED AIR CTL CMD to OFF?
When selected to OFF, the associated manifold pressure regulator valve closes and power is removed from the associated system.
How can the APU be used for starter-assisted main engine starts?
The APU may be used for starter-assisted main engine starts at and below 30,000 ft if required.
What are the limitations on the use of the APU for supplying pressurization airflow in flight?
The APU cannot be used to supply pressurization airflow in flight.
Test your knowledge of aircraft bleed air control units and their functions in regulating bleed air supply pressure and temperature for various aircraft systems. This quiz covers the operation and components of the BACs, including torque motors, fan air valves, and wing anti-ice valves.
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