TM 1-1520-264-23
6.2 FLIGHT CONTROL BELLCRANKS (ET).
6.2.1 Description (Figure 6-1. Index No. 2).
This inspection is applicable to all non-ferromagnetic bellcranks contained
within the flight control system.
6.2.2 Defects. The primary purpose of this inspection is for: (1) confirmation of crack indications identified by visual
inspections; (2) verification that scratches and gouges do not conceal cracks; and (3) ensure no cracks are present after
blend out procedures.
6.2.3 Primary Method. Eddy Current.
6.2.3.1 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
6.2.3.2 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 bellcranks using this procedure. If required, the bellcrank(s) shall be removed in accordance with the
applicable technical manuals listed in Table 1-1.
6.2.3.3 Access. Accessibility of the bellcranks varies considerably. Refer to Figure 1-4 and Table 1-2 to locate
applicable access provisions.
6.2.3.4 Preparation of Part. The part(s) shall be thoroughly cleaned. Refer to Preparation of Part or Area for NDI,
paragraph 1.4.4.
6.2.3.5 NDI Equipment Settings.
a.
Make the following initial settings on the Eddy Current Inspection Unit, NORTEC-19e
11
.
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.)
6-5
