TM 1-1520-265-23Change 3 2-492.21.3 PrimaryMethod. Eddy Current.2.21.3.1 NDI Equipment and Materials. (Refer to Appendix B.)a. Eddy Current Inspection Unitb. Probe, straight, shielded surface, 2 MHzc. Probe, right angle, shielded surface, 2 MHz, 90_ 1/2 inch dropd. Cable Assemblye. Adapter, Probe, 2 MHzf. Reference Block, three-notched titanium (0.008, 0.020, 0.040 EDM notches)g. Teflon Tape, refer to Table 1-8h. Aircraft Marking Pencil, refer to Table 1-82.21.3.2 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.) maybe performed on all exposed surfaces of the installed part using this procedure. If required, the mainrotor blade shall be removed in accordance with the applicable technical manuals listed in Table1-1.2.21.3.3 Access. Access to the main rotor blade cuff assembly is from the L/R engine cowl (Figure1-4, Items 3T-7 and 4T-8).2.21.3.4 Preparation of Part. The part shall be thoroughly cleaned. Refer to Preparation of Partor Area for NDI, paragraph 1.4.4.2.21.3.5 NDI Equipment Settings.a. Make the following initial settings on the Eddy Current Inspection Unit, NORTEC-19eII.Frequency F1 - 1000 KHz F2 - offHdB - 57.0VdB - 69.0Rot - 30_Probe drive - midLPF - 100HPF - 0H Pos - 80%V Pos - 20%b. 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 verticalsignal when probe is passed over 0.040-inch notch in test block. (See the standardinstrument display shown in Figure 1-7.)
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