FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 5. Nondestructive Inspection (NDI) | 7. Ultrasonic Inspection | 5-93. Basic Equipment
9/8/98
SECTION 7. ULTRASONIC INSPECTION
AC 43.13-1B
5-89. GENERAL. Ultrasonic inspection is
an NDI technique that uses sound energy
moving through the test specimen to detect
flaws. The sound energy passing through the
specimen will be displayed on a Cathode Ray
Tube (CRT), a Liquid Crystal Display (LCD)
computer data program, or video/camera me-
dium. Indications of the front and back sur-
face and internal/external conditions will ap-
pear as vertical signals on the CRT screen or
nodes of data in the computer test program.
There are three types of display patterns; “A”
scan, “B” scan, and “C” scan. Each scan pro-
vides a different picture or view of the speci-
men being tested. (See figure 5-15.)
5-90. SOUND REFLECTION.
The
amount of reflection that occurs when a sound
wave strikes an interface depends largely on
the physical state of the materials forming the
interface and to a lesser extent on the specific
physical properties of the material. For exam-
ple: sound waves are almost completely re-
flected at metal/gas interfaces; and partial re-
flection occurs at metal/liquid or metal/solid
interfaces.
5-91. ULTRASONIC INSPECTION
TECHNIQUES. Two basic ultrasonic in-
spection techniques are employed: pulse-echo
and through-transmission. (See figure 5-16.)
a. Pulse-Echo Inspection. This process
uses a transducer to both transmit and receive
the ultrasonic pulse. The received ultrasonic
pulses are separated by the time it takes the
sound to reach the different surfaces from
which it is reflected. The size (amplitude) of a
reflection is related to the size of the reflecting
surface. The pulse-echo ultrasonic response
pattern is analyzed on the basis of signal am-
plitude and separation.
b. Through-Transmission Inspection.
This inspection employs two transducers, one
to generate and a second to receive the ultra-
sound. A defect in the sound path between the
two transducers will interrupt the sound trans-
mission. The magnitude (the change in the
sound pulse amplitude) of the interruption is
used to evaluate test results. Through-
transmission inspection is less sensitive to
small defects than is pulse-echo inspection.
5-92. FLAW DETECTION. Ultrasonic in-
spection can easily detect flaws that produce
reflective interfaces. Ultrasonic inspection is
used to detect surface and subsurface disconti-
nuities, such as: cracks, shrinkage cavities,
bursts, flakes, pores, delaminations, and po-
rosity. It is also used to measure material
thickness and to inspect bonded structure for
bonding voids. Ultrasonic inspection can be
performed on raw material, billets, finished,
and semi-finished materials, welds, and in-
service assembled or disassembled parts. In-
clusions and other nonhomogeneous areas can
also be detected if they cause partial reflection
or scattering of the ultrasonic sound waves or
produce some other detectable effect on the
ultrasonic sound waves. Ultrasonic inspection
is one of the more widely-used methods of
NDI.
5-93. BASIC EQUIPMENT. Most ultra-
sonic inspection systems include the following
basic equipment; portable instruments (fre-
quency range 0.5 to 15 MHz), transducers
(longitudinal and shear wave), positioners, ref-
erence standards, and couplant.
a. Ultrasonic Instruments. A portable,
battery-powered ultrasonic instrument is used
for field inspection of airplane structure. (See
figure 5-17.) The instrument generates an
Par 5-89
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