TM 1-1520-253-23
a. Eddy Current Inspection Unit
b. Probe, straight, shielded surface, 100 KHz-500 KHz
c. Probe, right angle, shielded surface, 100 KHz-500 KHz, 901/2 inch drop
d. Cable Assembly
e. Reference Block, three-notched aluminum (0.008, 0.020, and 0.040 EDM notches)
f. Reference Block, three-notched magnesium (0.008, 0.020, and 0.040 EDM notches)
g. Teflon Tape, refer to Table 1-8
h. Aircraft Marking Pencil, refer to Table 1-8
2.3.3.2 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 hub oil tank shall be removed in accordance with the applicable
technical manuals listed in Table 1-1.
2.3.3.3 Access. Access is from the forward and aft transmission work platforms. See Figure 1-4 CH-47: 9, 27, and/or
34; MH-47: 16 and 17.
2.3.3.4 Preparation of Part. The hub oil tank outside surface shall be thoroughly cleaned. Refer to Preparation of Part
or Area for NDI, paragraph 1.4.4.
2.3.3.5 NDI Equipment Settings.
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a. Make the following initial settings on the Eddy Current Inspection Unit, NORTEC-19e .
Frequency F1
- 200 KHz
F2
- off
HdB
- 57.0
VdB
- 69.0
Rot
- 560
Probe drive
- mid
LPF
- 100
HPF
-0
H 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 vertical signal when
probe is passed over 0.040 inch notch in test block (Refer to standard instrument display shown in Figure
2-5
