R R R R R R R R R R R R R The Residual Pressure Control Unit (RPCU) 9HL controls the residual pressure in the cabin if: - There is a failure in the two automatic control parts of the CPCS - The CPCS is set to the manual mode. The RPCU opens the outflow valve automatically after landing if: - The outflow valve is not fully open - The CPCS is in manual mode or there is a failure of the two CPCs - The crew did not open the outflow valve in the manual mode. The RPCU is installed in the right-hand side of the avionics compartment. It uses the external relay 21HL to supply power directly to the manual motor of the outflow valve.
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B. Pressure Schedules The pressure schedules work with a dedicated rate limit to guarantee passenger comfort and safety at each flight phase. The control modes generate the operational phases for the cabin pressure schedules.
(1) Control Mode Logic (Ref. Fig. 002, 003) The system operates with the following control modes: GN - Ground, TO - Take-off, AB - Abort, CI - Climb, CR - Cruise, DI - Descent,
(2) Mode Logic
(a) Function (Ref. Fig. 004) The function of the mode logic is to determine the actual system mode using the various inputs.
(b) Switching Conditions (Ref. Fig. 003) The logic will switch to a specific mode depending on the condition of the aircraft.
(c) Mode Logic Switching (Ref. Fig. 002) Different mode logic switchings are possible:
Mode Logic Switching Figure 002
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Mode Logic Table Figure 003
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System Operation Logic Figure 004
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-'A' shows the complete mode logic switching range,
-'B' shows the mode logic switching for normal flight,
-'C' shows the mode logic switching for a flight where due to flight conditions (or air traffic control instructions). It is necessary to switch back from cruise to climb (or descent to climb). Switching from descent to cruise does not apply, because a change of the aircraft's cruise altitude can be done completely in FMGS in the cruise mode. If a descent is started, the cabin pressure starts to descend. It continues to descend (even if the aircraft descent is stopped because of a hold), until it gets to the maximum delta-P or the landing-field elevation (whichever is the lowest pressure).
-'D' shows the mode logic switching to give a realistic cabin pressure, if it is necessary to abort a takeoff or flight. It is also possible to return from the ground mode or the abort mode to the internal climb mode. This gives a good system performance under any conditions.
(3) Pressure Schedules and Rate Limits
(a)
Ground Mode (GN) The cabin pressure on the ground can never reach the scheduled pressure. This is because the scheduled pressure is always lower than actual cabin pressure. Therefore, the outflow valve is driven fully open.
(b)
Take-off Mode (TO) To avoid a pressure surge during aircraft rotation, the CPC prepressurizes the aircraft. At lift-off the CPC changes into the climb mode.
(c)
Climb Mode (CI) (Ref. Fig. 005, 006) In this mode the cabin pressure is controlled in relation to ambient pressure and aircraft climb speed. The control is based on a preprogrammed schedule, which schedules the change in cabin pressure to a change in ambient pressure. It is ensured that maximum differential pressure will not be reached during climb. A basic schedule is stored in a permanent memory.
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