TM 1-1520-253-23
2.4.3.2 Preparation of Helicopter. The helicopter shall be prepared for safe ground maintenance. Partial inspection for
cause (visual indications, sites of mechanical damage, corrosion, etc.) may be performed on all exposed surfaces of the
installed part using this procedure. If required, the pitch varying shaft shall be removed in accordance with the applicable
technical manuals listed in Table 1-1.
2.4.3.3 Access. Access is from forward and aft transmission work platforms. See Figure 1-4 -CH-47: 9, 27, and/or 34;
MH-47: 16 and 17.
2.4.3.4 Preparation of Part.
The part shall be thoroughly cleaned.
Refer to Preparation of Part or Area for NDI,
2.4.3.5 NDI Equipment Settings. Refer to Magnetic Particle Method, paragraph 1.4.8.
2.4.3.6 Inspection Procedure. A magnetic field shall be applied to the part perpendicular to the orientation of possible
cracks. Positions for this inspection are illustrated in Figure 2-4.
a. Select AC on the AC/DC power switch.
b. Place probe/yoke on part in Position 1 as shown.
c. Press the test switch and apply a light coat of magnetic particle media at the same time. Remove the media
momentarily before removing the current. Current should be applied for no more than five seconds.
d. Inspect for cracks using the black light.
e. Demagnetize before moving to the next position. Refer to paragraph 2.4.3.8.
f. Rotate the probe legs 90 degrees and repeat steps a. through e. for Position 2.
g. Place probe/yoke on part in Position 3 as shown.
h. Repeat steps a. through e. for Position 3.
i. Rotate the probe legs 90 degrees and repeat steps a. through e. for Position 4.
2.4.3.7 Marking and Recording of Inspection Results.
Mark and record the inspection results as necessary per
2.4.3.8 Demagnetization. With the switch remaining in the AC position, place the probe/yoke legs in the same position
used for magnetizing. Press the test switch and withdraw the probe/yoke from the part for a distance of two feet before
releasing the switch.
2.4.4 Backup Method. Fluorescent Penetrant, refer to paragraph 1.4.7.
2.4.5 System Securing. Clean the pitch varying shaft thoroughly to remove all residual magnetic particle media. Refer
to Post Cleaning and Restoration of Part or Area After NDI, paragraph 1.4.16. If removed, the pitch varying housing
requires installation in accordance with the applicable technical manuals listed in Table 1-1. Secure the forward and aft
transmission work platforms.
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