Pressurization

Question 1

what system controls the pressurization system

Answer 1

Cabin Pressure Control System

Question 2

how many automatic controllers are there in the Cabin Pressure Control System

Answer 2

2 (1 AUTO, 1 ALTN)

Question 3

what are the 2 primary valves used for pressurization control

Answer 3

• outflow valve
• overboard exhaust valve

Question 4

how many pressure relief valves are there

Answer 4

• 2 positive pressure relief valves
• 1 negative pressure relief valve

Question 5

what differential pressure do the positive pressure relief valves relieve to

Answer 5

9.1psi

Question 6

what does the negative pressure relief valve prevent

Answer 6

prevents outside air pressure > cabin pressure

Question 7

what are the 3 modes of operation for the pressurization system

Answer 7

• AUTO = AUTO control, normal mode of operation, uses DC motor
• ALTN = AUTO control, alternate mode of operation, uses DC motor
• MAN = MANUAL control of the system, uses DC motor

Question 8

what cabin altitude does the aircraft usually operate to at 41,000’

Answer 8

8,000’

Question 9

what data inputs do the automatic controllers receive to use AUTO/ALTN

Answer 9

• ADIRU data:
  
  • ambient static pressure
  • non-corrected baro altitude
  • corrected baro altitude
  • CAS
• stall management computer:
  
  • throttle position
• air/ground sensing

Question 10

what are all of the sources of pressurization outflow

Answer 10

• outflow valve
• overboard exhaust valve
• small amounts via:
  
  • LAV and GALLEY vents
  • misc vents
  • seal leakage

Question 11

where is air that arrives at the outflow valve from

Answer 11

1) cabin foot level grills; THEN
2) around AFT cargo compartment lining (heats AFT cargo)

Question 12

how does the overboard exhaust valve operate

Answer 12

• on ground/in-flight with low diff pressure:
  
  • full OPEN (E + E air sent overboard)
• in flight with large differential pressure:
  
  • full closed normally
    
    • however: the valve is driven open if:
      
      • either pack switch is in high; and
      • the right recirculation valve is OFF

Question 13

how often are each of the auto controllers sequenced as the primary controller

Answer 13

each flight

Question 14

what 2 settings may be set by the flight crew to control the auto pressurization

Answer 14

• FLT ALT
• LAND ALT

Question 15

what position is the outflow valve in on the ground with low power setting

Answer 15

full open

Question 16

when does the aircraft first begin pressurizing the aircraft

Answer 16

outflow valves begins to close at high power settings

Question 17

when is the cruise mode activated

Answer 17

pressure within 0.25psi of FLT ALT selected

Question 18

how is the pressure controlled in cruise mode

Answer 18

maintains lowest cabin altitude based on max cabin differential pressure as follows:
- FLT ALT at or below 28,000’ = 7.45psi
- FLT ALT 28,000’ to 37,000’ = 7.80psi
- FLT ALY > 37,000’ = 8.35psi

Question 19

when is descent mode activated

Answer 19

pressure 0.25psi below FLT ALT selected

Question 20

how is the pressure controlled in descent mode

Answer 20

cabin altitude reduces proportional to the aircraft altitude to slightly below the LAND ALT

Question 21

how is the pressure controlled in descent mode

Answer 21

cabin altitude reduces proportional to the aircraft altitude to slightly below the LAND ALT

Question 22

when taxiing in what happens to the outflow valve

Answer 22

slowly driven to full open

Question 23

what does an ‘AUTO FAIL’ light indicate

Answer 23

• loss of DC power
• controller failure
• outflow valve control fault
• excessive dpsi (8.75) [controller not responding properly]
• excessive cabin rate (2,000 mean sea level ‘/min [controller not responding properly]
• high cabin alt - 15,800’ [controller not responding properly]

Question 24

what happens to the system if the AUTO FAIL light illuminates

Answer 24

• automatically switches to the ALTN controller
• selecting the ALTN position will remove the AUTO FAIL light

Question 25

how is manual mode operation indicated

Answer 25

MANUAL light illuminates on overhead panel

Question 26

when is manual mode of operation used

Answer 26

• both AUTO and ALTN modes are inoperative
• non-normal situations

Question 27

how is cabin pressure controlled in manual mode of operation

Answer 27

flight crew manually select the position of the outflow valve via the outflow valve position switch

Question 28

is the operation of the outflow valve faster or slower in manual mode of operation compared to AUTO/ALTN

Answer 28

manual = faster (20s for full outflow valve range)

Question 29

what does the ‘OFF SCHED DESCENT’ light illuminate for

Answer 29

aircraft descended before reaching the intended FLT ALT

Question 30

what effect does the OFF SCHED DESCENT light have on the system

Answer 30

the controller programs the cabin to land at the takeoff field elevation without further pilot inputs unless the FLT ALT indicator is changed then it will abort this process

Question 31

‘AUTO FAIL’ light

Answer 31

• automatic pressurization system failure:
  
  • single controller failure when ‘ALTN’ light illuminated too
  • dual controller failure when illuminated alone

Question 32

‘OFF SCHED DESCENT’ light

Answer 32

airplane descended before reaching the planned cruise altitude set in the LFT ALT indicator

Question 33

‘FLT ALT’ indicator

Answer 33

• indicates selected cruise altitude (500’ increments)
• set before takeoff

Question 34

‘LAND ALT’ indicator

Answer 34

• indicated altitude of intended landing field (50’ increments)
• set before takeoff

Question 35

‘MANUAL’ light

Answer 35

pressurization system operating in manual mode of operation

Question 36

‘ALTN ‘ light

Answer 36

pressurization system operating in alternate mode of operation:
- if ‘AUTO FAIL’ also illuminated = single controller failure and automatic transfer
(AUTO FAIL’ disappears after selected to ALTN)
- pressurization mode sel in ALTN