Pressurization Flashcards
what system controls the pressurization system
Cabin Pressure Control System
how many automatic controllers are there in the Cabin Pressure Control System
2 (1 AUTO, 1 ALTN)
what are the 2 primary valves used for pressurization control
- outflow valve
- overboard exhaust valve
how many pressure relief valves are there
- 2 positive pressure relief valves
- 1 negative pressure relief valve
what differential pressure do the positive pressure relief valves relieve to
9.1psi
what does the negative pressure relief valve prevent
prevents outside air pressure > cabin pressure
what are the 3 modes of operation for the pressurization system
- 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
what cabin altitude does the aircraft usually operate to at 41,000’
8,000’
what data inputs do the automatic controllers receive to use AUTO/ALTN
- ADIRU data:
- ambient static pressure
- non-corrected baro altitude
- corrected baro altitude
- CAS
- stall management computer:
- throttle position
- air/ground sensing
what are all of the sources of pressurization outflow
- outflow valve
- overboard exhaust valve
- small amounts via:
- LAV and GALLEY vents
- misc vents
- seal leakage
where is air that arrives at the outflow valve from
1) cabin foot level grills; THEN
2) around AFT cargo compartment lining (heats AFT cargo)
how does the overboard exhaust valve operate
- 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
- however: the valve is driven open if:
- full closed normally
how often are each of the auto controllers sequenced as the primary controller
each flight
what 2 settings may be set by the flight crew to control the auto pressurization
- FLT ALT
- LAND ALT
what position is the outflow valve in on the ground with low power setting
full open
when does the aircraft first begin pressurizing the aircraft
outflow valves begins to close at high power settings
when is the cruise mode activated
pressure within 0.25psi of FLT ALT selected
how is the pressure controlled in cruise mode
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
when is descent mode activated
pressure 0.25psi below FLT ALT selected
how is the pressure controlled in descent mode
cabin altitude reduces proportional to the aircraft altitude to slightly below the LAND ALT
how is the pressure controlled in descent mode
cabin altitude reduces proportional to the aircraft altitude to slightly below the LAND ALT
when taxiing in what happens to the outflow valve
slowly driven to full open
what does an ‘AUTO FAIL’ light indicate
- 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]
what happens to the system if the AUTO FAIL light illuminates
- automatically switches to the ALTN controller
- selecting the ALTN position will remove the AUTO FAIL light
how is manual mode operation indicated
MANUAL light illuminates on overhead panel
when is manual mode of operation used
- both AUTO and ALTN modes are inoperative
- non-normal situations
how is cabin pressure controlled in manual mode of operation
flight crew manually select the position of the outflow valve via the outflow valve position switch
is the operation of the outflow valve faster or slower in manual mode of operation compared to AUTO/ALTN
manual = faster (20s for full outflow valve range)
what does the ‘OFF SCHED DESCENT’ light illuminate for
aircraft descended before reaching the intended FLT ALT
what effect does the OFF SCHED DESCENT light have on the system
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
‘AUTO FAIL’ light
- automatic pressurization system failure:
- single controller failure when ‘ALTN’ light illuminated too
- dual controller failure when illuminated alone
‘OFF SCHED DESCENT’ light
airplane descended before reaching the planned cruise altitude set in the LFT ALT indicator
‘FLT ALT’ indicator
- indicates selected cruise altitude (500’ increments)
- set before takeoff
‘LAND ALT’ indicator
- indicated altitude of intended landing field (50’ increments)
- set before takeoff
‘MANUAL’ light
pressurization system operating in manual mode of operation
‘ALTN ‘ light
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
