TM 1-1520-253-23
4.4.1 Description (Figure 4-1. Index No. 4). The forward transmission support structure is in the cockpit fuselage
structure assembly. The forward transmission support structure is made up of machined fittings spliced to sheet
aluminum webs and reinforced by formed and extruded parts.
4.4.2 Defects. Defects may occur anywhere on the surface of the structures. The primary purpose of this inspection is
to verify crack indications found visually. No cracks are allowed.
4.4.3
Primary Method. Eddy Current.
NDI Equipment and Materials. (Refer to Appendix B.)
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.
Teflon Tape, refer to Table 1-8
g. Aircraft Marking Pencil, refer to Table 1-8
4.4.3.2
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 transmission shall be removed in accordance with the applicable
technical manuals listed in Table 1-1.
4.4.3.3
Access. Access is from the forward transmission work platform. See Figure 1-4 - CH-47: 9; MH-47: 16.
4.4.3.4
Preparation of Part. The forward transmission support structure shall be thoroughly cleaned.
Refer to
Preparation of Part or Area for NDI, paragraph 1.4.4.
4.4.3.5
NDI Equipment Settings.
a. Make the following initial settings on the Eddy Current Inspection Unit, NORTEC-19ell.
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%
4-9
