TM 1-1520-265-23
4.31.3.2. 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 yoke shall be removed in accordance with the applicable technical
manuals listed in Table 1-1.
4.31.3.3. Access. Access to the upper yoke structure will require the removal of the tail landing gear fairings.
4.31.3.4. Preparation of Part. The part shall be thoroughly cleaned. Refer to Preparation of Part or Area for NDI,
paragraph 1.4.4.
4.31.3.5. NDI Equipment Settings.
a.
Make the following initial settings on the Eddy Current Inspection Unit, NORTEC-19e[".
Frequency Fl
- 200 KHz
F2
- off
HdB
- 57.0
VdB
- 69.0
Rot
- 56°
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. (See the standard instrument display shown in Figure
1-7.)
4.31.3.6 Inspection Procedure. Refer to Eddy Current Method, paragraph 1.4.11 and Figure 4-31.
a.
Place probe on a good area in the inspection location and null. Adjust phase as required to obtain horizontal lift-
off.
b.
Inspect the part.
c.
Any signal similar to the notches in the test block are cause for rejection.
NOTE
Either probe identified in paragraph 4.31.3.1 may be used depending primarily on the ease of
accessibility and user friendliness. If the probes are changed, steps 4.31.3.5 b. (1), (2), and (3)
shall be repeated each time a change is made.
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