TM 1-1520-253-23
3.19.3.2
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 engine transmission shall be removed in accordance with the
applicable technical manuals listed in Table 1-1.
3.19.3.3
Access. Access is from the aft transmission work platform. See Figure 1-4 - CH-47: 27 and/or 34; MH-47:
17.
3.19.3.4
Preparation of Part. The engine transmission shall be thoroughly cleaned. Refer to Preparation of Part or
Area for NDI, paragraph 1.4.4.
3.19.3.5
NDI Equipment Settings.
a. Make the following initial settings on the Eddy Current Inspection Unit, NORTEC-19elI.
Frequency F1
- 200 KHz
F2
- off
HdB
- 57.0
VdB
- 69.0
- 56
Rot
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 1-
3.19.3.6
Inspection Procedure. Refer to Eddy Current Method, paragraph 1.4.11 and Figure 3-19.
a. Place probe on part 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 is cause for rejection.
NOTE
Either probe identified in paragraph 3.19.3.1 may be used depending primarily on the ease of
accessibility and user friendliness. If the probes are changed, steps 3.19.3.5 b. (1), (2), and (3)
shall be repeated each time a change is made.
3-38
