TM 1-1520-253-23
COMBINING TRANSMISSION OUTSIDE SURFACE (ET).
3.16.1 Description (Figure 3-1. Index No. 16). The combining transmission receives input torque from the two engine
transmissions through the engine driveshafts. It combines the torque and transmits it to the forward and aft driveshafting
through output shafts.
3.16.2 Defects. Defects may occur anywhere on the surface of the combining transmission outside surface. Any
damaged area shall be inspected both before and after rework. No cracks are allowed.
3.16.3 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
3.16.3.2
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 combining transmission shall be removed in accordance with the
applicable technical manuals listed in Table 1-1.
3.16.3.3
Access. Access is through the combiner transmission door. See Figure 1-4 - CH-47: 23; MH-47: 30.
3.16.3.4
Preparation of Part. The area to be inspected shall be thoroughly cleaned. Refer to Preparation of Part or
Area for NDI, paragraph 1.4.4.
3.16.3.5
NDI Equipment Settings.
Make the following initial settings on the Eddy Current Inspection Unit, NORTEC-19elI.
a.
Frequency F1
- 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%
