TM 1-1520-253-23
2.8.4 Backup Method. Fluorescent Penetrant, refer to paragraph 1.4.7.
2.8.5 System Securing. Clean the horizontal hinge pin thoroughly to remove all residual magnetic particle media. Refer
to Post Cleaning and Restoration of Part or Area After NDI, paragraph 1.4.16. The horizontal hinge pin requires
installation in accordance with the applicable technical manuals listed in Table 1-1.
2.9.1 Description (Figure 2-1. Index No. 9). The centrifugal droop stop assembly is mounted in a splined plate under
the aft rotor head. The droop stop contains three balancing arms. These are connected by springs to lugs on the hub oil
tank. This inspection is to verify any cracks found visually.
2.9.2 Defects. Defects may occur anywhere on the surface of the centrifugal droop stop lugs. No cracks are allowed.
2.9.3 Primary Method. Eddy Current.
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
2.9.3.2 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 droop stop balancing arms shall be removed as required in
accordance with the applicable technical manuals listed in Table 1-1.
2.9.3.3 Access. Access is from the aft transmission work platform. See Figure 1-4 - CH-47: 27 and/or 34; MH-47: 17.
2.9.3.4 Preparation of Part. The centrifugal droop stop lugs shall be thoroughly cleaned. Refer to Preparation of Part or
Area for NDI, paragraph 1.4.4.
