(2)  
The second procedure tells to repair a long section of the heat duct. A long segment of duct is more than twelve inches (305 mm).

 C.  The heat duct is made from a BMI composite material. When you repair a short section of a composite heat duct, you must use a titanium sleeve to make the repairs. When you repair a long section of a composite heat duct, you must use a BMI composite material and two titanium sleeves to make the repairs.
 TASK 21-43-04-308-001
 2.  Forward Cargo Heat Duct Repairs (Fig. 801)_______________________________
 A.  Special Tools and Equipment
 (1)  
Commercially Pure Titanium - BMS 7-21, Grade II (Tubing or rolled sheet)

 (2)  
BMI duct segment - Long segment repair only (Same material as duct, kevlar reinforced epoxy laminate per BAC5575, grade A, class 4 using BMS8-264)

 (3)  
Scrivets - P/N 231-700055-00-3704,
 Fastex Co.
 195 East Algona Road
 Des Plains, Illinois 60191-1150

 (4)  
Mandril or ball (Mandril can be locally fabricated) - Short segment repair only

 B.  References
 (1)  IPC 21-43-01-01 Fig. 1
 C.  Access
 (1)  Location Zone 121 Forward Lower Lobe Compartment, Forward Half Left 122 Forward Lower Lobe Compartment, Forward Half Right 123 Forward Lower Lobe Compartment, Aft Half Left 124 Forward Lower Lobe Compartment, Aft Half Right
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A
747-400
MAINTENANCE MANUAL

FORWARD CARGO 
COMPARTMENT  FORWARD CARGO 
HEATERS (REF)  COMPARTMENT 
HEAT 
FORWARD CARGO 
HEAT DUCT 
INBOARD  SEE  B 
EXHAUST 
VALVE (REF) 
FORWARD CARGO 
HEATING  FORWARD CARGO HEATING 
SEE  A  A 

HEAT HEAT DUCTHEAT OUTLETOUTLET HOLESHOLES
FORWARD CARGO HEAT DUCT B
Forward Cargo Heating Duct - Repair Figure 801 (Sheet 1)
L02658
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A 747-400 MAINTENANCE MANUAL
REPAIR SEGMENT

SLEEVES
METHOD II - LONG SEGMENT REPAIR
NOTES:  CUT AND REMOVE DAMAGED SECTION TO ALLOW SUFFICIENT ACCESS FOR RIVETING REPAIR SECTION. SPACE SCRIVETS 1 TO 1-1/4 INCHES (25 TO 32 mm) APART WITH 0.35 INCH (9 mm) MINIMUM EDGE DISTANCE.
MAKE SURE HEAT OUTLET HOLES FACE UP.
HEAT CAN DAMAGE INSULATION IF OUTLET
HOLES ARE NOT POSITIONED CORRECTLY.

Forward Cargo Heating Duct - Repair
Figure 801 (Sheet 2)

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747-400 MAINTENANCE MANUAL
 D.  Procedure S 358-002
 (1)  Repair a Short Section of the Heat Duct (Procedure 1):
 NOTE: A short segment is twelve inches (305 mm) or less.

____ A long segment is greater than twelve inches (305 mm).
 (a)  
Remove the damaged heat duct.

 (b)  
Make an titanium sleeve which is 6 inches (152 mm) longer than the damaged heat duct.

 NOTE: The sleeve diameter must be larger than the heat duct
____ diameter. Push a mandril or a ball into the sleeve a minimum of 3 inches (76 mm) to increase the sleeve diameter, if it is necessary.
 (c)  
Drill the same number of the heat outlet holes in the sleeve that are in the damaged heat duct.

 (d)  
Loosen the duct support clamps to permit the installation of the sleeve.

 (e)  
Install the sleeve as shown in Figure 801. NOTE: Make sure the heat outlet holes are on the top of the
　
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