(1)
If the pack controller 7HH (27HH) primary computer fails the secondary computer controls at a reduced level. The ram-air inlet doors will open to the maximum flight position and no further optimization takes place, (the flow control reference remains at its previous setting). Control of the water-extractor outlet temperature (to the level demanded from the zone controller 8HK) will still take place through modulation of the bypass valve 10HH (30HH). The overheat warning will still be available.
(2)
If the zone controller 8HK (or its communications) fail completely the pack controllers 7HH (27HH) take over control. They will limit the water extractor outlet temperature to 20 DEG.C (68.00 DEG.F) for pack 1 (10HM) and to 10 DEG.C (50.00 DEG.F) for pack 2 (11HM). If there is a failure (of the communications from the zone controller main computer and it remains active), the pack controllers take over control. They will limit the water extractor outlet temperature to 5 DEG.C (41.00 DEG.F) for pack 1 and to 10 DEG.C (50.00 DEG.F) for pack
2. The zone controller can still use the trim-air system (Ref.
21-63-00) to increase the cabin inlet temperature, if necessary. The
pack controllers still get the zone controller status signal from the
zone secondary computer.
A flow priority mode is included in the pack controller primary
computer. At low pack inlet pressure the bypass valve 10HH (30HH)
(and the ram-air inlet doors) are modulated to a more open position
and thus increase pack permeability.
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(3) The pack controller will detect a failure of the bypass valve function when:
-
the bypass valve fails (either because of a valve actuator failure or because of a valve jam),
-
the power output circuit of the primary channel fails.
In both cases the secondary channel of the pack controller takes the
control and opens the ram air inlet doors to a limited position.
If the power output circuit was the faulty function, the temperature
will be controlled by the secondary channel and the bypass valve.
If the bypass valve failure is effective, the ram air inlet doors are
controlled to a limited open position by the secondary channel to
avoid overheating of the compressor.
A failure of the primary channel of the pack controller is indicated
on the CFDS by the message P1 CONT or P2 CONT.
R **ON A/C 401-499,
A. Normal Operation The ACSC computes from the selected temperature, the altitude correction and eventually a FAP offset, a target temperature. The ACSC compares the target temperature with the measured water extractor outlet temperature and determines the bypass valve drive speed and direction. The speed is zero, when the water extractor outlet temperature gets to the required value and the bypass valve to the preferred position. The preferred bypass valve 10HH (30HH) position is normally 21 DEG. but is adjusted when necessary, dependent on pack inlet pressure. The water-extractor outlet temperatures are limited to prevent blockage by icingand too high stress. The upper limit is 70 DEG.C (158.00 DEG.F). The lower limits are as follows:
(1) One or two packs operation
----------------------------------------------------------------------------| 0 to 20000 ft | 5 DEG.C (41 DEG.F) | |--------------------------------------|-------------------------------------| | 20000 to 28000 ft | slope between 5 DEG.C (41 DEG.F) | | | and 0 DEG.C (32 DEG.F) | |--------------------------------------|-------------------------------------| | 28000 ft to 30000 ft | slope between 0 DEG.C (32 DEG.F) | | | and -30 DEG.C (-22 DEG.F) | --------------------------------------|-------------------------------------| above 30000 ft | -30 DEG.C (-22 DEG.F) | --------------------------------------|-------------------------------------
(2) Compressor outlet temperature limits
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