that can cause cracks is not permitted. d) Airfoil damage that causes a deformation is not permitted.
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(j)
(k)
(l)
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747-400 MAINTENANCE MANUAL
e) Sulfidation that decreases the strength of the blade is not permitted.
NOTE: Sulfidation can be divided into four steps.
____ These steps give the initial damage to failure. The four steps are described as follows:
Step 1.______ Light Sulfidation - The metal is not smooth on the surface. This is caused by some growth of oxide scales. Local deterioration of the scale layers show. The strength of the metal is not changed.
Step 2.______ Bad Sulfidation - The metal is more rough and the oxide scale layers continue to deteriorate. The strength of the metal is not changed.
Step 3.______ Oxide Failure - Liquid sodium sulfate shows below the oxide scale layers. The oxide scales show. The blade will have a failure.
Step 4.______ Very Bad Damage - The blade has large cavitation in the metal. The oxide scales are large. The blade will have a failure.
Slowly turn the eyepiece one full turn while you move the borescope tip to fully examine the leading and trailing edges of the turbine vane ring, and the inner and outer rings of the vane ring assembly.
NOTE: It can be necessary to use the side view adapter to
____ do a full inspection. Also, because the vane ring does not turn, do the full inspection through the right and the left igniter plug ports.
1) Stator drum cracks are permitted.
2) Leading edge cracks on the stator vanes are not permitted.
3) Trailing edge cracks less than one quarter of the vane
chord are permitted. a) There is no limit on the number of trailing edge cracks. 4) Cracks in a vane which can cause a piece of the vane to break off are not permitted.
5) Erosion or corrosion on the leading or trailing edge of a blade, larger than 10 percent of the vane chord, is not permitted.
When you complete the inspection, carefully remove the borescope and the guide tube from the igniter plug port.Install the PWC 41492 guide tube in the other igniter plug port and do steps (d) through (k) again.
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747-400 MAINTENANCE MANUAL
(m)
Do this task for the two igniter plugs: "Igniter Plug Installation" (Ref 49-41-04/401).
(n)
Install a new packing on the crank cover for the high turbine.
(o)
Install the crank cover on the rear of the accessory gearbox housing with the two washers and the nuts (Fig. 601). 1) Tighten the nuts to 36-40 pound-inches (4.0-4.5 N.m).
S 296-008
(8)
Do the borescope inspection of the power turbine (Fig. 606):
(a)
Remove the two bolts that attach the borescope inspection cover for the power turbine to the exhaust duct.
(b)
Remove the borescope inspection cover with the PWC 41325-001 puller.
CAUTION:_______DO NOT USE FORCE TO INSTALL THE GUIDE TUBE. THE GUIDE TUBE MUST EASILY INSTALL IN THE PORT. DAMAGE TO THE GUIDE TUBE CAN OCCUR.
(c)
Install the PWC 41491 guide tube in the borescope inspection port for the power turbine. 1) Attach the guide tube to the boss.
CAUTION:_______BE VERY CAREFUL WITH THE BORESCOPE DEVICE. THIS DEVICE CAN BE EASILY DAMAGED. DO NOT TWIST OR HOLD THE DEVICE TIGHTLY. DO NOT LET THE BORESCOPE DEVICE FALL TO THE GROUND. DAMAGE TO THE BORESCOPE CAN OCCUR.
(d)
Connect the fiberscope cable to the light source.
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