Bleed Air Control

Question 1

RAM DOOR FULL OPEN light

Answer 1

• ram door (modulation panel) is in full open position
• on the ground, or airborne with flaps extended
• ram air door modulation is a function of air/ground sensor, flaps, and compressor discharge temperature
• normal position in flight with the flaps up is faired (closed) to decrease drag
• if the light is on during cruise it may be one of these 3 possible problems:
• ram air system may have blockage
• heat exchangers are dirty
• electrical failure

Question 2

RECIRC FAN switches

Answer 2

AUTO
in-flight
- with both packs in AUTO, both recirc fans operate
- if either PACK switch is in HIGH the left recirc fan shuts down
- if both PACK switches are in HIGH, the right recirc fan shuts down
on the ground
- with both packs in AUTO, both recirc fans operate (same as in flight)
- if either PACK switch is in HIGH, both recirc fans continue to operate
- if both PACK switches are in HIGH the left recirc fan shuts down
- the right recirc fan continues to operate

Question 3

WING-BODY OVERHEAT TEST switch

Answer 3

• pressing does a check of the continuity of the sensing elements
• if the sensing element has continuity both WING-BODY OVERHEAT lights illuminate
• same as a real alarm
• MASTER CAUTION and AIR COND annunciator lights illuminate
• if the sensing element does not have continuity, there are no indications
• there is no difference between a real alarm and a short circuit

Question 4

PACK switch (L and R)

Answer 4

AUTO
- with both packs operating, each pack regulates to normal air flow (normal scenario)
- with only one pack operating, that pack regulates to high flow in-flight with the flaps up to maintain necessary ventilation rate
- this auto-switching to high flow is inhibited on the ground, or in-flight with flaps extended
- in the air, it’s for better single engine performance
HIGH
- pack regulates to high flow mode
Regulates to APU high flow mode when
- aircraft is on the ground
- APU bleed switch is ON and
- either or both pack switches are in HIGH
- the APU is capable of supplying bleed air for 2 packs on the ground, or 1 pack in flight

Question 5

ISOLATION VALVE switch

Answer 5

CLOSE / OPEN
- isolation valve is closed or opened
AUTO
- isolation valve is closed if all corner switches are ON, which is normal
- isolation valve is open if any corner switch (pack or bleed) is in the OFF position

Question 6

PACK lights (L and R) (amber)

Answer 6

• indicates both primary and standby pack controls have failed, or
• respective pack has exceeded limits and has tripped off
  Function of
• compressor discharge overheat (390°F/199°C)
• turbine inlet overheat (210°F/99°C) or
• pack discharge overheat (250°F/121°C)
• related pack flow control & SOV closes
• if the PACK light illuminates during MASTER CAUTION recall, a single failure of either primary or standby pack control has occurred

Question 7

WING-BODY OVERHEAT light (L and R)

Answer 7

• LEFT
• indicates overheat from a bleed air duct leak in the left engine pylon, left inboard wing leading edge, left air conditioning bay, keel beam or APU bleed air duct
• RIGHT
• same items as above except no keel beam or APU bleed air (right engine strut, right wing leading edge, right air conditioning bay)

Question 8

BLEED TRIP OFF light (L and R) (amber)

Answer 8

• excessive engine bleed air temp (254°C/490°F) or pressure (220 psi)
• engine bleed valve closes and pack valve closes, which drives the mix valve full cold
• light remains illuminated until TRIP RESET switch is pushed
• after this light comes on, you will see zero pressure on that side of the system

Question 9

ENGINE BLEED AIR switch (L and R)

Answer 9

• the switch is armed only if the engine fire handle is down (normal condition)
  OFF
• control signal closes the bleed air regulator (BAR) solenoid valve which closes the pressure regulator and SOV (bleed valve)
  ON
• the control signal goes through the ACAU and opens the BAR solenoid valve which opens the PRSOV if the engine is operating
• BAR is DC powered and controls the PRSOV pneumatically
• spring loaded closed with no pneumatic pressure

Question 10

APU BLEED AIR switch

Answer 10

OFF 
-	closes the APU bleed air valve
ON 
-	opens the bleed air valve
-	DC power (control) and APU load compressor air required to open and stay open

Question 11

TRIP RESET

Answer 11

• press if the fault condition has been corrected
• lights remain illuminated until reset
• resets
  ZONE TEMP
  PACK, and
  BLEED TRIP OFF
• does not reset the WING-BODY OVERHEAT

Question 12

DUAL BLEED light (amber)

Answer 12

• illuminated indicates APU bleed valve is open and
• engine #1 bleed switch on or
• engine #2 bleed switch on and isolation valve open
• when APU bleed switch is positioned off, dual bleed light will go out when the APU bleed valve closes