*
Schedule 1 maximum is calculated for 440 seats.
*
Schedule 1 minimum is calculated for 348 seats.
Airplanes with less seats use the schedule 1 minimum as the amount of air that the CTC controls to.
The total air flow into the airplane can go above the calculated value for schedule 1 if any of these conditions occur:
* Off or inoperative recirculation fan, total flow increases approximately 67 lb/min for each fan that is not on.
Flow Schedule 2
Flow schedule 2 is related to the maximum number of passenger seats. The calculated rate of air flow is based on 81 percent of the maximum possible number of passenger seats. When the ASCPC commands schedule 2, the actual air flow rate that the CTC controls to is the schedule 2 rate or the schedule 1 rate, whichever is less. One pack can give the total air flow necessary for schedule 2.
For airplanes with seating configurations more that 81 percent of the maximum, schedule 2 limits the amount of air the pack provides into the airplane to a value less than schedule 1.
For airplanes with seating configurations less than 81 percent of the maximum, the actual air flow rates for schedules 1 and 2 are the same.
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AIR CONDITIONING -PACK FLOW CONTROL -FUNCTIONAL DESCRIPTION -PACK FLOW SCHEDULES
Flow Schedule 3
Flow schedule 3 is related to the maximum number of passenger seats. The calculated rate of air flow is based on 50 percent of the maximum possible number of passenger seats.
Flow Schedule 4
Flow schedule 4 gives the minimum flow to pressurize the airplane and to operate the air cycle machine. The flow rate has a relation to the airplane altitude.
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General
The ASCPC sets the flow schedules for the left and right CTCs. The left ASCPC is primary for this function, and the right ASCPC is the backup. The CTCs use the flow schedule data to calculate the amount of air to send to the packs.
The ASCPC has an ARINC 629 interface with other systems and LRUs. These interfaces give the ASCPC data about airplane operating conditions and about other bleed air users. The ASCPC uses these inputs to set the pack air flow schedules.
The ASCPC sends the selected flow schedules to the CTCs through the left and right ARINC 629 systems buses (not shown).
Flow Schedules
Flow schedule 1 gives the greatest airflow to the air conditioning packs and is the usual flow schedule.
Schedules 2, 3, and 4 give less and less air to the packs. In general, these schedules are in effect for one or more of these conditions:
*
The amount of bleed air available is less than usual
*
More than the usual number of bleed air user systems are on
*
Takeoff or single engine operation.
When the APU supplies air to the pack, schedules 3 and 4 are not used. Also, if the forward or aft cargo fire switches are armed, schedules 3 and 4 are not used.
Schedule 0 stops the air flow into the packs. During an engine start on the ground, the packs shut off to make air available to the starter. The packs stay off for 2 minutes to allow time to start the two engines. For a stall warning during takeoff, schedule 0 makes sure the air driven hydraulic pumps get enough air for auto-slat deployment.
Training Information Point
If you start just one engine, the pack does not operate until two minutes after the start. The pack OFF light stays on during the two minutes.
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