TM 1-1520-253-23
AIRFRAME STRUCTURES (ET).
4.3.1 Description (Figure 4-1. Index No, 3). This inspection is applicable to all decking, panel and door skins,
bulkheads, formers, stringers, supports, beams, and longerons constructed with nonferrous material.
4.3.2 Defects. Defects may occur anywhere on the surface of the airframe structures listed above. The primary
purpose of this inspection is for: (1) confirmation of crack indications identified by usual inspection; (2) verification that
dents, scratches, or gouges do not conceal cracks; and (3) locating the ends of confirmed cracks so that stop drilling may
be performed. No cracks are allowed.
4.3.3
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
Probe, right angle, shielded surface, 100 KHz-500 KHz, 901/2 inch drop
c.
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
4.3.3.2
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 removable airframe structures shall be removed in accordance
with the applicable technical manuals listed in Table 1-1.
4.3.3.3
Access. Refer to paragraph 1.1.9, Figure 1-4, and Table 1-2 to locate applicable access panels and fairings.
WARNING
Maintenance Platforms/Workstands
Use only appropriate platforms, workstands, or other approved locally procured stands and
restraint equipment when working above 10 feet on helicopters in a nontactical environment.
Otherwise, personnel injury could result from accidental falls.
4.3.3.4
Preparation of Part. The area of interest shall be thoroughly cleaned. Refer to Preparation of Part or Area
for NDl, paragraph 1.4.4.
4-6
