FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 5. Nondestructive Inspection (NDI) | 3. Eddy Current Inspection | 5-28. Surface Inspection
AC 43.13-1B
9/8/98
FIGURE 5-5. Typical instrument displays.
Service-induced cracks in aircraft structures
are generally caused by fatigue or stress corro-
sion. Both types of cracks initiate at the sur-
face of a part. If this surface is accessible, a
high-frequency eddy current inspection can be
performed with a minimum of part preparation
and a high degree of sensitivity. If the surface
is less accessible, such as in a subsurface layer
of structure, low-frequency eddy current in-
spection can usually be performed. Eddy cur-
rent inspection can usually be performed with-
out removing surface coatings such as primer,
paint, and anodic films. Eddy current inspec-
tion has the greatest application for inspecting
small localized areas where possible crack ini-
tiation is suspected rather than for scanning
broad areas for randomly-oriented cracks.
However, in some instances it is more eco-
nomical to scan relatively large areas with
eddy current rather than strip surface coatings,
inspect by other methods, and then refinish.
5-28. SURFACE INSPECTION. Eddy
current inspection techniques are used to in-
spect for surface cracks such as those shown in
figure 5-6.
FIGURE 5-6. Typical surface cracks.
a. Equipment Requirements. The fol-
lowing are typical eddy current equipment re-
quirements for surface crack inspections.
(1) Instruments must meet the liftoff
and sensitivity requirements of the applicable
NDI procedures. The frequency requirement is
generally 100 Hz to 200 kHz.
(2) Many types of probes are available
such as: flat-surface; spring-loaded; pencil;
shielded pencil; right-angle pencil; or fastener
hole probes.
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