including stage, area, magnitude, direction, and
Establish internal reference points. Pictorial
adjacent material conditions. Some inspection
and cutaway diagrams help establish these
cards instruct you to mark or bend an 18-inch
reference points. When the probe is in the inspec-
length of lockwire, and then insert the wire
tion port, it is easy to lose your sense of direc-
through an adjacent inspection port. You can then
tion. Some borescopes have an index mark on the
use this wire as a gauge to measure vane cracks
eyepiece to show direction.
while viewing through the borescope.
Figures 9-17 and 9-18 show different engine
Scan the inspection area thoroughly and
parts seen through a borescope. You must know
in an orderly manner. Compressor cracks can be
the words to describe the damage found. Then
difficult to detect because of small close parts,
compare this information with serviceability
rotating the engine too fast, or because of
limits in the maintenance instruction manuals. See
deteriorated borescope optics. Note and evaluate
table 9-4.
any inconsistencies. Record all information,
Table 9-4.-Examples Of Serviceability Limits
9-21
