Pressurisation

Question 1

What components make up the pressurisation system?

Answer 1

-2 CPCs
-Outflow valve (actuator with 3 motors)
-2 safety valves
-One control panel

Question 2

How does the pressurisation system operate?

Answer 2

One CPC functions at a time & they switch 70 seconds after landing. Cabin altitude is controlled by varying the position of the outflow valve which stores of releases pressure from in the cabin supplied by the air conditioning system.

Question 3

Name the 4 modes of a pressurisation cycle?

Answer 3

Ground mode - before TO and 55s after landing, outflow valve fully open
Pre-pressurisation - during TO roll, pre pressurises cabin to 0.1 psi to prevent rotation surge
Pressurisation (CLB, Cruise & DES)
De-pressurisation - Occurs at touchdown which releases any cabin over pressure at +500ft/min and then 55s after landing back into ground mode and outflow valve fully open

Question 4

When does Pressurisation mode become active and how does it function during climb, cruise & descent?

Answer 4

CLB mode becomes active at lift off, cabin is pressurised at a schedule based on climb rate
Cruise mode cabin altitude is maintained at the altitude at level off or LDG elevation whichever is higher
DES mode the system calculates a descent schedule based on LDG elevation and the QNH in MCDU perf page so at landing cab alt is 0.1psi above ambient. Max ROD is 750ft/min

Question 5

When do depressurisation and ground modes activate?

Answer 5

Depressurisation mode occurs at touchdown which released any overpressure at 500ft/min. Ground mode 55s after touchdown and outflow valve fully opens.

Question 6

Max cabin altitude in automatic pressurisation mode?

Answer 6

8000ft

Question 7

What does the pressurisation system use in auto mode as a reference for LDG elevation?

Answer 7

Landing elevation from FMGC and QNH from perf page. If MCDU not available will use captain Baro ref and LDG elevation manually set

Question 8

How is manual pressurisation control achieved?

Answer 8

Pressuring manual override p/b on overhead. Power is cut to the two auto motors connected to outflow valve & 3rd motor for manual mode is energised. Cabin alt now adjusted using toggle switch which adjust outflow valve position. Pressurisation schedule now likely to be displayed on ECAM.

Question 9

What pressurisation system advisories are in the QRH?

Answer 9

Cabin vertical speed >1880ft/min
Cabin altitude >8800ft/min
Cab diff pressure > 1.5 PSI in phase 7