Pneumatics

Question 1

What are the different sources of bleed air for the ECS?

Answer 1

The Environmental Control System recieves bleed air from the LP (p2.7) and HP (P3) Compressor Port of the Engines, or the APU.

Question 2

Describe the ECS ECU.

Answer 2

• In the Avionics Bay
• Serves as an interface between Control Inputs and the mechanical and electrical components of the BAS.
• Two redundant digital and analog channels.

Question 3

Describe the Digital Channels of the ECS ECU.

Answer 3

• Control the HP and LP bleed ports.
• They monitor protective sensors to maintain proper temperatures, pressures, flow rates, and positions of various BAS valves.

Question 4

Describe the Analog Channels of the ECS ECU.

Answer 4

• They are the backup.
• They only control the LP Port.
• (The HPSOV will be closed)

Question 5

What dos the BLEED 1 & 2 ON / OFF Switches do?

Answer 5

Selecting these switches ON turns on the respective BAS by energizing the respective NSOV.

Question 6

How does the Rotary Action Bleed Air Selector Knob regulate airflow?

Answer 6

It modulates the NSOVs at MIN, NORM, or MAX levels.

Question 7

Why and how is Bleed Air cooled?

Answer 7

Bleed air, especially from the HP port, may be too hot for ACM or De-Ice use. Therefore it passes through an air-to-air preecooler where P2.2 air is used as a coolant. Each side has a single unit with two stages – A High Stage Preecooler and De-Ice Preecooler.

Question 8

What does a BLEED HOT Caution Light Indicate?

Answer 8

• It indicates that the air just prior to the NSOV is too hot, possibly due to the P2.2 SOV being too restrictive (not enough air on the cooling side of the precooler) or the P3 SOV being opened too much (too much hot air on the other side of the precooler). The ECU will then close the NSOV until the overtemp condition is corrected.
• It could also indicate an overpressure situation past the NSOV.

Question 9

What conditions will cause the ECU to automatically close the NSOV?

Answer 9

• Bleed Air Overtemp Switch, just past the High Stage Precooler.
• Duct Leak Overtemp Switch, just past the NSOV.
• Bleed Overpressure Switch, downstream of the NSOV.

Question 10

What indication will you get with a Duct Leak?

Answer 10

None. The ECU closes the NSOV and sends a fault code to the Central Diagnostic System.