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permitted.
5) Examine the cooling rings for cracks (View B., Item B., Fig. 607). a) Cracks larger than 0.010 inches (0.25 mm) in width are
not permitted. b) Cracks between four or more cooling holes are not permitted (View A., Fig. 607). c) Cracks between two or more rows of cooling holes are not permitted (View A., Fig. 607). d) Cracks that can possibly cause material to break are not permitted.
6) Examine the fuel nozzle bosses and the igniter plug bosses for cracks. a) Cracks are not peritted.
7) Examine the seam welds for cracks. (View B., Item D., Fig. 607). a) More than five cracks are not permitted. b) More than three cracks in any one seam weld are not
permitted. c) Cracks in a seam weld can be a maximum of 0.3 inches
(7.6 mm) in length. d) More than three cracks adjacent to a seam weld are not
permitted. e) Cracks adjacent to a seam weld can be a maximum of
1.0 inches (25.4 mm) in length.
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747-400 MAINTENANCE MANUAL
f) Cracks adjacent to the seam can be a maximum of 0.03 inches (0.8 mm) in width.
8) Examine the remaining wall linings and butt welds for cracks (View B., Items E. and F., Fig. 607). a) More than five cracks in a panel are not permitted. b) Cracks in a panel must point in the same direction. c) Cracks in a panel must be a minimum of 3.0 inches (76.2
mm) apart. d) Cracks in a panel must not be longer than 1.0 inch
(25.4 mm). e) Cracks in a panel must not be larger than 0.03 inches
(0.8 mm) in width.
9) Examine the remaining wall linings and butt welds for buckling (View B., Items E. and F., Fig. 607). a) Local buckling that does not have a large depth is
permitted. b) Buckling with a sudden change of the contour (kinks) is not permitted. c) The buckling of burned walls that cause a reduction in wall thickness is not permitted.
10) Look for burned through holes in the remaining combustion wall linings and the butt welds (View B., Items E. and F., Fig. 607). a) A maximum of five burned through holes with a maximum
diameter of 0.125 inches (3.0 mm) permitted. b) The burned through holes must be separated by at least
3.0 inches (76.2 mm).
c) Two or more burned through holes that align in the axial direction are not permitted.
(g)
Carefully remove the borescope.
(h)
Install the igniter plug (Ref 49-41-04/401).
S 866-010
(10)
Remove the DO-NOT-CLOSE tags and close these circuit breakers:
(a)
P83 Panel, E8 Aft Equipment Center
1) APU PRIMARY CONT
(b)
P6 Main Power Supply Panel
1) 6K18 APU ALTN CONT
S 866-011
(11) Remove the DO-NOT-OPERATE tag from the APU control switch on the P5 panel.
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S 616-015
(12)
Do the Auxiliary Power Unit - Servicing (Oil Replenishing) procedure (MM 12-13-02/301).
S 796-014
(13)
Do a leak check for APU oil:
(a)
Operate the APU (MM 49-11-00/201).
(b)
Examine the APU for leaks.
(c)
Do the APU shutdown procedure (MM 49-11-00/201).
S 416-009
(14)
Close the APU access doors:
(a)
Do a visual check of the EGT bus bars: 1) Make sure the bus bars are not damaged. 2) Make sure no metal parts touch the bus bars. 3) Make sure the bus bars do not touch each other.
(b)
Disengage the support rods for the APU access doors.
(c)
Put the support rods in the clips on the inner side of the APU access doors.
(d)
Make sure the insulation covers attach correctly to the APU compartment firewall.
(e)
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