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 CAUTION:_______USE EXTREME CARE WHEN YOU HANDLE PNEUMATIC DUCTS. IF DAMAGED, TITANIUM DUCTS MAY CRACK UNDER PRESSURE AND RESULT IN POSSIBLE DAMAGE TO AIRPLANE AND EQUIPMENT.
 C.  The duct sections of the pneumatic, air conditioning, and thermal anti-icing systems can be replaced or removed for repairs. Some of the duct sections are designed slightly short, in order to compensate for thermal expansion when hot air flows through the ducts. The ducts should not be hot when installed and must be slightly prestressed by the clamps at the duct joints.
 D.  When the ducts are reinstalled on the airplane, align the duct such that the mating center lines are in axial alignment to within 0.06 inch, unless otherwise noted.
 E.  To prevent interference or chafing conditions, make sure there is a minimum of 0.25-inch clearance between the bare pneumatic duct and the adjacent structures and there is a minimum of 0.75-inch clearance between the bare pneumatic duct and systems (i.e., hydraulic lines, fuel lines, etc.). If clearance between the bare pneumatic duct and systems is found to be less than 0.75 inch, make the following adjustments:
 (1)  
Make the necessary adjustments to the duct installation (i.e., duct support rods) to obtain 0.75-inch clearance.

 (2)  
If it is not possible to obtain 0.75-inch clearance after an attempt to make the necessary adjustments to the duct installation, make the adjustments to adjacent system installations (i.e., hydraulic lines, fuel lines, etc.) to obtain 0.75-inch clearance.

 (3)  
If it is still not possible to obtain 0.75-inch clearance after all attempts at adjustments, but a clearance of 0.50 inch can be obtained between the bare pneumatic duct and systems, note the area where there is less than 0.75-inch clearance in a maintenance checklist and inspect the area of interest on a periodic basis.

 F.  
The pneumatic ducts are joined by these methods:

 (1)  
Rigid joints or V-band clamps are used to connect ducts in the wing leading edge, air conditioning bay, and APU pneumatic duct sections. This joint connection is rigid and does not allow the ducts to be misaligned.

 (2)  
Flexible joints are used to connect ducts in wing leading edge and engine strut where allowance for duct misalignment is necessary.

 (3)  
Sliding joints are used in the wing leading edge to connect ducts where the effects of wing flexure and thermal expansion have to be taken into consideration. This joint connection allows one duct to slide inside another duct.

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 36-11-01
 ALL  ú ú 02 Page 401 ú Oct 18/01
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

 (4)  Ball joints are used at the high stage manifold duct to provide seal at duct joints where the effects of thermal expansion and engine vibration has to be taken into consideration. This joint connection is slightly flexibility to allow the ducts to pivot at the joint.
 G. This procedure is subdivided by the type of duct section installation:
 (1)
Removal and installation of a duct section with a sliding joint.

 (2)
Removal and installation of a duct section with a ball joint.

 (3)
Removal and installation of a duct section with a rigid joint.

 (4)
Removal and installation of a duct section with a flexible joint.

 (5)  
Removal and installation of the wing leading edge T-duct section.

 (6)  
Installation of a complete set of ducts on the wing leading edge.

 (7)  
Installation of wing leading edge flap drive duct clamp.

 (8)  
Removal and Installation of the APU Duct Restraints.

 TASK 36-11-01-004-001
 2.  Duct Section with a Sliding Joint Removal (Fig 402)_________________________________________
 A. References
 (1)  
AMM 27-81-00/201, Leading Edge Flap System

 (2)  
AMM 36-00-00/201, Pneumatic System

 B. Prepare to Remove the Duct Section
 S 864-047
 WARNING: MAKE SURE ALL PERSONS AND EQUIPMENT ARE AWAY FROM THE LE AND TE
_______ FLAPS AND THE FLAP DRIVE MECHANISM BEFORE YOU MOVE THE CONTROL LEVER FOR THE FLAPS. WHEN YOU REMOVE THE HYDRAULIC POWER, THE ELECTRICAL POWER WILL CAUSE THE FLAPS TO MOVE AUTOMATICALLY WHEN THE CONTROL LEVER FOR THE FLAPS IS MOVED. THIS CAN CAUSE INJURIES TO PERSONS OR DAMAGE TO EQUIPMENT.
　
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