Pneumatics

Question 1

Bleed Air System (BAS)
• Part of the Environmental Control System (ECS)
• Bleed air can be supplied by: (2)
• Systems that use pneumatic power:
(4)

Answer 1

• Part of the Environmental Control System (ECS)
• Bleed air can be supplied by:
o	Engines
o	Auxiliary Power Unit (APU) prior to engine start (ground operations only)
• Systems that use pneumatic power:
o	Air Conditioning & Pressurization
o	Airframe De-icing
o	Air stair door seal 
o	Engine oil cooling ejection system

Question 2

Bleed Air System (BAS)
• Bleed air from the engines is ducted from the ___ and the ___
• ___ and the ___ determine which engine bleed port is to be used
• ECU has a left ___ channel with a left backup ___ channel and a right ___ channel with a right backup ___ channel
o Digital Channels - control the ___
o Analog channels - serve as a backup and are only able to control ___
• ___ Bleed air is use to actuate the “exterior oil cooler door”. Door opens when: (3)

Answer 2

• Bleed air from the engines is ducted from the Low-Pressure (LP) compressor port and the High-pressure (HP) compressor port
• Power lever position and the Environmental Control System ECU (Electronic Control Unit) determine which engine bleed port is to be used
• ECU has a left digital channel with a left backup analog channel and a right digital channel with a right backup analog channel
o Digital Channels - control the LP and HP bleed ports of their respective engines
o Analog channels - serve as a backup and are only able to control LP engine bleed air operations
• P2.7 Bleed air is use to actuate the “exterior oil cooler door”. Door opens when:
o Aircraft is on the ground
o Oil temperature > 100°C
o PLA

Question 3

High Stage Precooler Operation

- How is HP bleed air (P3.0) cooled

Answer 3

• At some higher engine power settings, the HP bleed air (P3.0) can be too hot for use by the ECS, airframe deice system and oil cooler ejectors
• Cooling air from the P2.2 engine bleed port is routed through a High Stage precooler and used to reduce the temperature of the HP bleed air (P3.0)
• When necessary, the ECU opens the P2.2 Shutoff valve to allow the P2.2 bleed air to go through the precooler and then it is vented overboard
• High stage precoolers operate independently on each side of the aircraft

Question 4

Deice Precooler Operation
• Deice precoolers are incorporated in both engine bleed systems to reduce the temperature of the bleed air going to the airframe deice system
• Continuous flow of ___ bleed air is routed through the deice precoolers to reduce the temperature of both LP (___) and HP bleed air before it goes to the deice system
• ___ bleed air is vented overboard once it passes through the deice precoolers
• ___ is always running for use of the de-ice system (boots)

Answer 4

• Deice precoolers are incorporated in both engine bleed systems to reduce the temperature of the bleed air going to the airframe deice system
• Continuous flow of P2.2 bleed air is routed through the deice precoolers to reduce the temperature of both LP (P2.7) and HP bleed air before it goes to the deice system
• P2.2 bleed air is vented overboard once it passes through the deice precoolers
• P2.7 is always running for use of the de-ice system (boots)

Question 5

BAS Abnormal Operations
Bleed Air Overtemperature
• An over temperature switch is installed in the bleed supply duct ___ to monitor the temperature of the bleed air just prior to the ___
• If it senses that the bleed air temperature is too high, it signals the ECU to close the ___ until the temperature returns to normal
• ___ Caution light illuminates

Answer 5

• An over temperature switch is installed in the bleed supply duct downstream of the High Stage Precooler to monitor the temperature of the bleed air just prior to the NSOV (Nacelle Shutoff Valve)
• If it senses that the bleed air temperature is too high, it signals the ECU to close the NSOV until the temperature returns to normal
• “(1) or (2) BLEED HOT” Caution light illuminates

Question 6

BAS Abnormal Operations
Nacelle Duct Leak Overtemperature
• Nacelle Duct Leak Overtemperature switches are installed in the bleed air supply duct downstream ___
• System signals ECU to close the ___ and sends a fault code to the Central Diagnostic System to identify the duct leak
• ___ Caution light illuminates

Answer 6

• Nacelle Duct Leak Overtemperature switches are installed in the bleed air supply duct downstream of the NSOV
• System signals ECU to close the NSOV and sends a fault code to the Central Diagnostic System to identify the duct leak
• “(1) or (2) BLEED HOT” Caution light illuminates

Question 7

BAS Abnormal Operations
Bleed Overpressure
• Overpressure switch is also installed in the bleed supply duct ___
• If bleed air pressure is too high, it signals the ECU to close the ___
• ___ Caution light illuminates

Answer 7

• Overpressure switch is also installed in the bleed supply duct downstream of the NSOV
• If bleed air pressure is too high, it signals the ECU to close the NSOV
• “(1) or (2) BLEED HOT” Caution light illuminates