Systems - Pneumatics and Pressurization

Question 1

Describe pack valve operational logic.

Answer 1

Packs will automatically close if any of the following conditions occur:
[LIPP EEGO]
1 Pack Shuts Down:           
- Loss of bleed source
- Icing below 24,600'
- Pack overload
- Pack overheat

2 Packs Shut Down:

• Essential power
• Engine start
• Go around
• One engine inop below 9,700’

Question 2

Where is engine bleed air supplied from?

Answer 2

High pressure compressor stages 9 and 14

Question 3

When does the high stage valve automatically open?

Answer 3

• low engine thrust ops
• engine cross bleed start
• anti-ice operations

Question 4

In flight, with both PACKS off, how does the cabin receive air?

Answer 4

Via the ram air inlets. Ram air valves open allowing ram air to be routed to the distribution lines.

Question 5

What is the purpose of the automatic takeoff pressurization sequence?

Answer 5

Avoid pressure bumps after takeoff.

Question 6

Can you turn the gasper fan off on the ground?

Answer 6

No because the avionics compartment uses the gasper fan for cooling.

Question 7

Describe theoretical cabin altitude.

Answer 7

Keeps the cabin pressure as low as possible following takeoff while maintaining a rate of change to hit 7.8 psid at 37,000’.

Question 8

When does the aircraft begin to pressurize on the ground?

Answer 8

As soon as the engine 1 thrust lever is set to THRUST SET position or above.
(Causes cabin altitude to descend toward an altitude equivalent to 0.2 psi below takeoff altitude.)

Question 9

What is the duration of the pressurization takeoff sequence?

Answer 9

15 minutes or until theoretical cabin altitude becomes greater than actual cabin altitude, whichever occurs first.

Question 10

Where does the pressurization system receive static pressure from?

Answer 10

Pressurization static ports on the aft fuselage

Question 11

How are the Environmental Control Units (ECUs) of the PACKs cooled in flight?

Answer 11

External air drawn by the air cycle machine fans, supported by ram air from the NACA inlets.

Question 12

Where are indications of cabin altitude, differential pressure, and cabin rate of change found?

Answer 12

EICAS

Question 13

With the pressurization system in AUTO, when will the cabin altitude increase upon landing?

Answer 13

Opening the main cabin door or turning off the air conditioning.