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R  Each air conditioning pack has a flow control valve which gives 
R  variable flow and shut off control. These valves are 
R  electro-pneumatically operated. 
R  They will open when the PACK 1 (2) pushbutton switches are pushed in 
R  (the OFF legends go off) if the conditions which follow exist: 
R  - the engines are not in a starting sequence, 
R  - an ENGINE FIRE pushbutton switch is in the normal position (the 
R  light in the pushbutton switch is off), 
R  - the DITCHING pushbutton switch 13HL is released (the ON legend is 
R  off), 
R  - the bleed air pressure is more than the minimum pressure needed to 
R  open the flow control valves. 
R  (2) Normal Operation (packs running on engine bleed supply) 
R  When the PACK 1 (2) pushbutton switches 7HB (6HB) are pushed in (the 
R  OFF legends go off) the flow control valves open. 
R  The crew selects the PACK FLOW selector 5HB to the LO, NORM or HI 
R  position. 
R  - This position selects the flow control reference in the ACSC 47HH 
R  (57HH) to 80%, 100% or 120%. 
R  - The ACSC calculates the necessary flow and then sets the flow 
R  control valves 23HB (24HB) to the demanded position. 
R  When the PACK FLOW selector is set to the LO position, and the 
R  temperature demand cannot be reached, the ACSC will increase the 
R  normal airflow of the flow control valve from 80% to 100%. 
R  (3) APU in Operation (packs running on APU bleed air supply) 
R  When the PACK 1 (2) pushbutton switches 7HB (6HB) are pushed in (the 
R  OFF legends go off) the flow control valves open. 
R  The ACSC 47HH (57HH) receives the APU bleed valve open signal. 
R  The flow control reference in the ACSC is set to 120% and the flow 
R  control valves are commanded to the fully open position. 
R  (4) Single Pack Operation (pack running on engine or APU bleed air 
R  supply) 
R  When a pack pushbutton switch is pushed in (the OFF legend goes off) 
R  the respective flow control valve opens. 
R  Irrespective of which position the PACK FLOW selector is set to, the 
R  ACSC will modulate the pack to the 120% (HI) mode. Thus the flow 
R  control valve is commanded to the fully open position. 

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R  (5) Operation with Failures 
R  (a) Single Pack Failure 
R  When the PACK FLOW selector is set to the NORM or LO position and 
R  there is a failure in one pack, the ACSC modulates the other pack 
R  to the 120% (HI) mode. Thus the flow control valve is commanded 
R  to the fully open position. 
R  (b) Engine Fire 
R  If there is an engine fire, and you push the applicable FIRE 
R  pushbutton switch, the respective flow control valve closes. This 
R  stops the hot bleed air flow in order to prevent damage to the 
R  components of the air conditioning system and to prevent entry of 
R  smoke into the cabin. 
R  (c) Ditching 
R  In case of landing on water the DITCHING pushbutton switch must 
R  be pushed. This closes the flow control valves which prevents the 
R  entry of water into the cabin through the air conditioning 
R  system. 
R  (d) Air-Cycle Machine Compressor Overheat 
R  If the compressor of an air-cycle machine exceeds 215 deg.C 
R  (419.00 deg.F), the ACSC and flow control valve will start to 
R  reduce the pack flow independent of the flow demand till the 
R  minimum flow demand is reached. 
R  When the compressor temperature reaches 260 deg.C (500.00 deg.F) 
R  (overheats) on ground, the ACSC will shut off the pack (flow 
R  control valve is closed). 
R  (e) Pack Shut-down in the Engine-Start Sequence 
R  In the engine-start sequence (the EIU gives an engine rpm-signal 
R  of N1<50%), normally both air-packs close. 
R  To prevent the complete pack shut-down in flight because of a 
R  wrong EIU-signal, the crossbleed valve indication relay 7HV 
R  monitors the position of the Cross Bleed Valve (CBV) 6HV: 
R  - If the CBV is in the closed position, only one pack instead of 
　
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