AFT CARGO HEATING SYSTEM

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AFT CARGO HEATING SYSTEM
BY 744 FO ALPHA
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System consists of
AFT Cargo Heat

• a control valve
• a override valve
• a temperature selector switch
• two temperature control switches
• an overheat switch.

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System consists of
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Aft Cargo Heat Valve Override Valve
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Aft Cargo Heat Spray Tube
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Functional Description

• Normal Operation
• The override valve is open when
• all of these conditions exist
• - The aft cargo heat switch is on
• - The aft cargo fire switch is normal
• - The overheat switch in the aft cargo
  compartment
• senses a temperature less 90F/32C
• - The CMC ground test is not active.

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Normal Operation
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Normal Operation

• The aft cargo control valve works depend on the
  aft cargo air conditioning system is on or off.

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Normal Operation (continue)

• When the air conditioning system is on, the aft
  cargo air conditioning system puts temperature
  controlled air into the compartment through
  louvers in the ceiling.
• The control valve close

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Normal Operation (continue)

• When the aft cargo air conditioning system is
  off, the control valve cycles to maintain the
  selected switch temperatures.

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Normal Operation (continue)

• But when the compartment is very full of cargo,
  the temperature near the floor of the compartment
  can be too cold. If the underfloor switch senses
  a temperature less than 40F/4C, the control
  valve opens and bleed air heats the floor.

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Underfloor switch
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Under floor Temperature Control Switch

• The underfloor temperature control switch is only
• active when aft cargo air conditioning is on.
  
• Usually, the aft cargo heat control valve is
  closed when aft cargo air conditioning is on.
• But when the cargo compartments are full, the
  floor can be much colder than the rest of the
  compartment. If the temperature under the floor
  decreases to 40F/4C, the aft cargo heat control
  valve opens.

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Temperature Sensor
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Temp. switch set points

• SWITCH OPEN
  CLOSE
• Low 50F (10C) max
  40F (4C) min
• High 75F (24C) max
  65F (18C) min
• OR
• 60F (16C) max
  50F (10C) min
• Overheat 80F (26C) min
  90F (32C) max

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Compartment Overheat

• If the overheat switch senses a temperature
  greater
• than 90F/32C in the compartment
• Closes the override valve.
• Enables the TEMP light on the P5 panel and the
  OVHT
• input to the ECS MISC Card.
• During hot ambient conditions, this is a normal
• condition unless the control valve is open.
• So if the control valve is closed, the aft
  cargo overheat
• inhibit relay, R8467, inhibits overheat
  indications.

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Temperature Indicator
The aft and bulk compartment temperatures is an
average value and show as one temperature for the
aft compartment.
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Aft Cargo Fire Arm
If the crew arms the aft cargo fire switch, the
cargo heat fire shutoff relay, R235, energizes.
This closes overheat and control valves.
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AFT CARGO AIR CONDITIONING
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AFT CARGO AIR CONDITIONING
Aft Cargo Trim Air
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(No Transcript)
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AFT CARGO AIR CONDITIONING
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Aft cargo air conditioning selected off
- the aft cabin shutoff valve is open, and the
aft cargo FRV is closed pack 2 is in normal or
high flow in relation to conditions
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Aft cargo air conditioning selected low
- the aft cabin shutoff valve is open, and the
aft cargo FRV does a modulation open
approximately half of the pack 2 air goes to the
plenum, and the other half goes to the cargo
compartment the pack 2 operates in high flow
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Aft cargo air conditioning selected high

• the aft cabin shutoff valve is closed, and the
  aft cargo FRV
• does a modulation open all pack 2 air goes to
  the cargo
• compartment pack 2 discharge temperature set as
  necessary
• for the cargo compartment, and the trim air
  modulating valve
• is closed pack 2 operates in high flow.

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Temperature Control of Aft Lower Lobe Cargo With
Loss of Trim Air

• CASE 1
• if the Aft Lower Lobe Temperature selector
  setting is available to the PTC, pack two outlet
  temperature is regulated to achieve the
  temperature set by the selector

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Case 1
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Temperature Control of Aft Lower Lobe Cargo With
Loss of Trim Air

• CASE 2
• if the Aft Lower Lobe Temperature selector
  setting is unavailable to the PTC, pack two
  outlet temperature is regulated to achieve the
  cargo temperature sensed at the time backup mode
  was initiated

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Case 2
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Temperature Control of Aft Lower Lobe Cargo With
Loss of Trim Air

• CASE 3
• if aft lower lobe temperature is unavailable to
  the PTC, pack two outlet temperature is
  controlled to the outlet temperature sensed at
  the time backup mode was initiated.

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Case 3
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Case 1 Case 2
Case 3
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AFT CARGO VENTILLATION FANS
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AFT CARGO VENTILLATION FANS

• Two vent fans improve air circulation in the aft
  and bulk cargo compartments during these two
  conditions
• - during cargo loading
• - in flight, if the aft cargo air conditioning
• system fails.
• The fans draw air from outside the cargo
  compartment
• liner and send it into the compartments
  through the air
• conditioning ducts.

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AFT CARGO VENTILLATION FANS
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AFT CARGO VENTILLATION FANS

• Ground Operation
• All of these condition must exist to turn on
  the fans
• during ground operations
• - The vent fan control switch must be on
• - The airplane must be on the ground
• - All cargo fire switches must be in the
  normal position
• - The aft cargo air conditioning system must
  be off
• - The aft or bulk cargo door must not be
  closed.

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AFT CARGO VENTILLATION FANS

• Flight Operation
• All of these condition must exist to turn the
  fans on in flight
• - The vent fan control switch must be on
• - The airplane must be in flight
• - All cargo fire switches must be in the
  normal position
• - The aft cargo air conditioning system must
  be selected on
• but not operating.

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summary
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THANK YOU