Distortion. Distortion or bowing of the liner
assemblies is extremely difficult to assess when viewed
through the borescope.
If an axial streak (gutter) is
observed to be out of contour, estimate the relative
distortion in terms of dimples spanned or in relation to
the diameter of the dilution holes. If the distortion is
present at the No. 1 band, estimate the contour change
at the dome band relative to the panel.
Inspect the HP turbine for eroded or burned areas,
cracks or tears, nicks or dents, and missing blades.
Knifing (erosion resulting in sharp edges) can occur on
first-stage blades. The severity will vary according to
the cleanliness of the turbine inlet air. Check for pitting
on the leading edge near the root of the second-stage
Cracking of the first-stage nozzle guide vanes is not
very common, but photograph and report any suspected
cracks. First-stage vane surfaces at the juncture of the
inner and outer platforms have a tendency to corrode or
erode. It would not be unusual for you to find several
small penetrations in a vane platform during its service
life. Most of these penetrations remain small and are
not usually severe enough to warrant engine
Record any such penetrations and
regularly inspect them for any changes in size or
Vane HP (concave) surfaces will show gradual
erosion with time, and the trailing edge slots will
When this degradation reaches
maximum service limits, as noted on the PMS card or
in the manufacturers technical manual, the engine must
HP turbine second-stage blades have a service life
that is dependent upon operating conditions. Cracks are
the major inspection criteria listed. You should
document and report any confirmed cracks. The most
common form of degradation is deposit buildup and
erosion; this is not usually as severe as on the first-stage
blades. The most serious form of damage that you may
find in this area is pitting in the root area, which you
must document and report. For reference to the parts
nomenclature used in this section, refer to figure 2-11,
sections D and E.
HP TURBINE NOZZLE DAMAGE. T h e
first-stage turbine nozzle vanes are inspected
simultaneously with the combustor and fuel nozzles.
The following paragraphs describe the common damage
you may find during the borescope inspections.
Discoloration. Normal aging of the HP turbine
nozzle stage 1 vanes will result in coloration changes as
operating time is accrued. There is no limit relative to
discoloration of HP turbine nozzle vanes.
Oxidation and/or burning of the vane areas is
accompanied by dark areas silhouetting the initial
distress. Cracks are shrouded in dark patches adjacent
to the defect. Usually the distress starts as a crack,
followed by oxidation of the shroud adjacent to the
crack Impact damage usually shows as a dark spot on
the leading edge.
Leading Edge Damage. This type of damage can
be found between the forward gill holes on the concave
and convex side of the leading edge.
Axial cracks form around the leading edge.
Estimate the percent of span of the leading edge
or span relative to the nose cooling hole rows to
determine the crack length.
Burns and spalling on the leading edge should not
be construed as coloration only, but must have
actual metal oxidized (surface metal loss), but no
holes through the leading edge. Estimate the area
boundaries by the nose cooling holes spanned
both radially (up and down the leading edge) and
axially (around or across the leading edge).
Record the number of vanes affected.
Blocked cooling air passages on the leading edge
is another type of damage. If multiple hole
blockage is observed, record the separation of the
open cooling holes and the number of adjacent
Airfoil Concave Surface. Radial cracks run
spanwise in the vane airfoil surface (up and down the
vane). Record the relative chord position of the cracks.
Record the relation of axial cracking versus radial
cracking, such as axial and radial cracks that intersect
or join at the second row of gill holes. The intent of the
service limits are to preclude the liberation (break-out)
of pressure facepieces.
Other Airfoil Area Defects. The following
paragraphs describe other airfoil area defects that you
may find during the inspections.
Burns and cracks on concave and convex sides
(charred). Record the area and length, estimate
the length relative to the leading edge area (gill
hole to gill hole and spanwise by span of cooling
or gill holes).
Estimate the surface damage