TM 1-1520-264-23
2.10.3.8
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.
2.10.4
Backup Method. None required.
2.10.5
System Securing. Clean the main rotor hub retention nut thoroughly to remove all residual magnetic particle
media. Refer to Post Cleaning and Restoration of Part or Area After NDI, paragraph 1.4.16. The main rotor hub retention
nut requires installation in accordance with the applicable technical manuals listed in Table 1-1.
2.11
MAIN ROTOR HEAD (HUB) (ET).
2.11.1
Description (Figure 2-1. Index No. 11). The main rotor head assembly is a fully-articulated assembly that
provides attachment points for the four main rotor blade assemblies.
2.11.2
Defects. This inspection is used to verify crack indications found visually on the main rotor head (hub). No
cracks are allowed.
2.11.3
Primary Method. Eddy Current.
2.11.3.1
NDI Equipment and Materials. (Refer to Appendix B.)
a.
Eddy Current Inspection Unit
b.
Probe, straight, shielded surface, 100 KHz-500 KHz
c.
Probe, right angle, shielded surface, 100 KHz-500 KHz, 90
1/2 inch drop
d.
Cable Assembly
e.
Reference Block, three-notched aluminum (0.008, 0.020, and 0.040 EDM notches)
f.
Teflon Tape, refer to Table 1-8
g.
Aircraft Marking Pencil, refer to Table 1-8
2.11.3.2
Preparation of Helicopter. The helicopter shall be prepared for safe ground maintenance. A 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 main rotor head (hub) shall be removed in accordance
with the applicable technical manuals listed in Table 1-1.
2.11.3.3
Access. Not applicable.
2.11.3.4
Preparation of Part. The part shall be thoroughly cleaned. Refer to Preparation of Part or Area for NDI,
paragraph 1.4.4.
2.11.3.5
NDI Equipment Settings.
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