MAIN ROTOR HUB BEARING (ET).
Description (Figure 2-1. Index No. 2-19). The main rotor hub bearing provides a hinge point for the lead lag
Defects. This inspection is used to verify crack indications found visually on the main rotor hub bearing. No
cracks are allowed.
Primary Method. Eddy Current.
NDI Equipment and Materials. (Refer to Appendix B.)
Eddy Current Inspection Unit
Probe, straight, shielded surface, 100 KHz-500 KHz
Probe, right angle, shielded surface, 100 KHz-500 KHz, 90 °
1/2 inch drop
Reference Block, three-notched aluminum (0.008, 0.020, and 0.040 EDM notches)
Teflon Tape, refer to Table 1-8
Aircraft Marking Pencil, refer to Table 1-8
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 hub bearing shall be removed in accordance with the
applicable technical manuals listed in Table 1-1.
Access. Not applicable.
Preparation of Part. The part shall be thoroughly cleaned. Refer to Preparation of Part or Area for NDI,
NDI Equipment Settings.
Make the following initial settings on the Eddy Current Inspection Unit, NORTEC-1 9e11.
- 200 KHz
Probe drive - mid
Refer to Eddy Current Method, paragraph 1.4.11. Set up on test block as follows:
(1) Null probe on test block.
(2) Adjust phase as required to obtain horizontal lift-off.
(3) Move probe over all three notches in test block. Adjust gain to obtain a three block vertical signal when probe
is passed over 0.040-inch notch in test block. (See the standard instrument display shown in Figure 1-7.)