1)  Adjust the light intensity to make the light brighter if it is necessary.
 CAUTION: MAKE SURE THE ACTUATOR LEVER FOR THE DISTAL TIP IS IN THE
_______ NEUTRAL POSITION WHEN YOU INSTALL OR REMOVE THE BORESCOPE. THIS WILL PERMIT THE TIP TO MOVE FREELY IN THE GUIDE TUBE.
 CAUTION: MAKE SURE YOU LET 40 MINUTES GO BY AFTER AN ENGINE
_______ SHUTDOWN BEFORE YOU DO THE INSPECTION. DAMAGE TO THE FIBERSCOPE CAN OCCUR IF THE APU IS TOO HOT.
 (e)  Slowly install the borescope tip in the guide tube while you look through the eyepiece. 1) Stop the installation when you can see the power turbine
 blades.
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A 747-400 MAINTENANCE MANUAL 
A 
DUCT EXHAUST 
BOLT  A COVER  ASEE HOLE T6 THERMOCOUPLE POWER TURBINE
A 

(LOAD ROTOR) TURBINE POWER 
INSPECTED AREA  (INSTALLED AT GUIDE TUBE 5:30 POSITION) 
A-A Power Turbine Borescope Inspection Figure 606 

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A
747-400
MAINTENANCE MANUAL

 (f)  
Loosen the knurled knob on the PWC 41393 fixture.

 (g)  
Align the distal tip and turn the eyepiece slowly to examine the tip, the root, and the airfoil section of the power turbine blades.

 (h)  
If it is installed, remove the crank cover for the load compressor from the front of the load gearbox housing (Fig. 601): 1) Remove the two bolts and the washers that attach the crank

 cover to the load gearbox housing. 2) Remove the crank cover with the PWC 41350 puller. 3) Remove and discard the packing.
 CAUTION: MAKE SURE THE BORESCOPE DISTAL TIP DOES NOT ENGAGE THE
_______ POWER TURBINE BLADES. DAMAGE TO THE BLADES AND THE BORESCOPE CAN OCCUR WHEN YOU TURN THE LOAD SECTION.
 (i)  
Attach a wrench to the square end socket of the gear shaft.

 (j)  
Examine the power turbine while a different person slowly turns the load rotor with the wrench: 1) Visually examine the power turbine to make sure it is in

 the inspection limits that follow:
 a) Blades that have coating loss are permitted.
 b) Cracks in the blades are not permitted.
 c) Bad foreign object damage (FOD) and/or blade tip damage

 that can cause cracks is not permitted. d) Airfoil damage that causes a deformation is not permitted. 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.
 Stage 2._______ Bad Sulfidation - The metal is more rough and the oxide scale layers continue to deteriorate. The strength of the metal is not changed.
 Stage 3._______ Oxide Failure - Liquid sodium sulfate shows below the oxide scale layers. The oxide scales show. The blade will have a failure.
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A
747-400 MAINTENANCE MANUAL
 Stage 4._______ Very Bad Damage - The blade has large cavitation in the metal. The oxide scales are large. The blade will have a failure.
 f) Pushed in blade surfaces are not permitted.
 (k)  Visually examine the stator vanes for the power turbine to make sure they are in the inspection limits that follow: 1) Stator drum cracks are permitted. 2) Leading edge cracks less that one quarter of the vane chord
　
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