Table of Contents:-

Normal Operations (Refer to Chapter 4)

Alternate Operations
  • Bleed Air Overheat Light Illuminated
  • High Stage Bleed Air Valve Failure

Controls and Indicators
  • Pneumatic System
  • Wing LE Overheat

  • Pneumatic System

Supplementary Information


Alternate Operations
Bleed Air Overheat Light Illuminated:
Bleed Air Valve Switch ..... Close
Check VALVE CLOSED light illuminates, OVERHEAT light extinguishes.
Note:  The OVERHEAT light may take up to 60 seconds to extinguish.
If OVERHEAT light remains illuminated.
Trust lever ..... Retard
Flight conditions permitting, retard Thrust Lever until overheat light extinguishes.  With the OVERHEAT light illuminated, Thrust Lever at IDLE and other engine and pneumatic indications normal, the engine may be operated at IDLE.

High Stage Bleed Air Valve Failure:-

High Stage Valve Failed Closed:
This condition is indicated by one HIGH STAGE light extinguished and three lights illuminated.  In icing conditions, if possible, maintain at least 70% N1 RPM in level flight.  In descent during prolonged icing, periodically accelerate affected engine to 70% N1 RPM.

High Stage Valve Failed Open:
This condition is indicated by one HIGH STAGE light illuminated and three lights extinguished.
No action is necessary.

Controls and Indicators
Pneumatic System

Bleed Air Overheat Light (Amber):
Illuminates if bleed air temperature is excessive.

Bleed Air Valve Closed Light (Amber):
Illuminated whenever engine bleed air valve is fully closed.

Duct Isolation Valve Switch:
Isolated wing ducts from rest of the pneumatic system.

Bleed Air Valve Switch:
In open position the valve:
- regulates engine bleed air pressure to 45psi maximum.
- modulates and if necessary closes for excessive bleed air temperatures
- prevents reverse flow except when ignition switch is in the ground start positions.
In close position:
- shuts off engine bleed air supply
- closes high stage bleed air valve

Duct Pressure Indicator:
Displays left and right pneumatic duct pressure.  Sensors are located outboard of isolation valves.

High Stage Light (Green):
Indicates high stage bleed valve has automatically opened to replace low stage bleed.
High stage bleed is used for
pneumatic air supply during low thrust operation.

Wing LE Overheat

Wing Overheat Test Switch:
Test A - Momentary position.  Checks electrical continuity to all detectors.  Both LEFT and RIGHT WING OVERHEAT lights illuminate if circuit satisfactory.
Test B - The wing overheat lights illuminate for this test position, but no detector circuits checked.
Wing Overheat Lights (Amber):
Indicates pneumatic duct leakage in associated wing or engine struts.

Pneumatic System

Supplementary Information
General Description:
Engine compressor bleed air is utilized for cabin pressurization, air conditioning, thermal anti-icing of the wing leading edges and the engines, pneumatic drives for leading edge flaps, after cargo compartment heat, main deck cargo smoke detector and air driven hydraulic pumps.  Additional engine bleed air sources are used for engine fan thrust reverser operation.

The pneumatic  system automatically selects either high or low stage bleed air from the engine compressor and delivers pressure regulated and temperature limited air to the pneumatic duct.  Normally during takeoff, climb, cruise and most holding conditions the system draws low stage air.  For descent and other low engine thrust conditions the high stage is required to provide for system demand.

Bleed air temperature is normally controlled by a "precooler" which utilizes engine fan air to cool the bleed air.


Pneumatic source: 8th and 14th stage compressor (15th for P/W) bleeds, APU or Ground carts

7 Pneumatic users:

  • Engine start
  • Packs
  • Pressurize Cabin, Hydraulic Reservoirs & Water tank
  • LE Flaps
  • ADP Hydraulic pumps
  • Wing anti-ice
  • Aft cargo heat.