TM 1-1520-264-23
6.38
DIRECTIONAL F.S. 348 BELLCRANK (ET).
6.38.1
Description (Figure 6-1. Index No. 38). The directional F.S. 348 bellcrank attaches the forward and
directional control push-pull rods in the F.S. 348 area.
6.38.2
Defects. This inspection is used to verify crack indications found visually on the directional F.S. 348
bellcrank. No cracks are allowed.
6.38.3
Primary Method. Eddy Current.
6.38.3.1
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, 90 1/2 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
6.38.3.2
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 directional F.S. 348 bellcrank shall be removed in accordance with
the applicable technical manuals listed in Table 1-1.
6.38.3.3
Access. Access is through the tail rotor shaft and deck area fairings (Figure 1-4, Items T325 and T355).
6.38.3.4
Preparation of Part. The part shall be thoroughly cleaned. Refer to Preparation of Part or Area for NDI,
paragraph 1.4.4.
6.38.3.5
NDI Equipment Settings.
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
- 56°
Probe drive - mid
LPF
- 100
HPF
- 0
H Pos
- 80%
VPos
- 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.)
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