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.

HP Turbine 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 blading.

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 replacement. Record any such penetrations and regularly inspect them for any changes in size or quantity.

Vane HP (concave) surfaces will show gradual erosion with time, and the trailing edge slots will become elongated. When this degradation reaches maximum service limits, as noted on the PMS card or in the manufacturer's technical manual, the engine must be replaced.

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.- The 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 plugged holes.

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 relative to separation of gill hole rows and radially by gill or cooling holes.

Craze cracking. These cracks are superficial surface cracks, caused by high temperature. They are random lines that are very thin in appearance with tight lines (no depth or width to the cracks). There is no limit against this condition.

Nicks, scores, scratches, or dents. These defects are allowed by the service limit and may "be present on any area of the nozzle vanes.

Cracks in the airfoil fillet at the platform. There is no limit restricting these cracks, except at the leading edge area.

Metal splatter. Aluminum and combustor liner metal, when liberated by the compressor or combustor, frequently splatter the surface areas of the stage 1 HP turbine nozzle vanes. There is no limit for these deposits; however, abnormal amounts of this splatter is reason to inspect the compressor.

Platforms.- Cracking in the HP turbine nozzle stage 1 platforms is difficult to see from the combustor borescope ports. When this area is viewed through port No. 12, extreme magnification is afforded even with probe No. 2. This is due to the closeness of the surface to the distal end of the probe. Record the origin and end of the cracking and assess the magnitude using trailing edge slots and gill hole rows for radial and axial dimensions.

Nicks, scores, scratches, and dents on platform surfaces are again masked from the combustor ports, except for the forward areas. Viewed via port No. 12, the area is magnified. Record the magnitude of the defect using the geometry of the trailing edge, gill hole rows, and gill hole separation for comparative dimensions.

You must record burns on vane platform areas and use probe No. 1 to assess the conditions. If a burn-through occurs, the inner and outer surface edge of the platform should be seen. This difficult assessment can be done with the aid of a fiberscope. Any incomplete or doubtful evaluation should be the subject of a followup check after a specified amount of operating time.

HP TURBINE BLADE DAMAGE.- When inspecting the HP turbine blades, you should use probe No. 2 with the 150-watt light source. The following paragraphs describe some of the damage you may find.

Cracks in the Leading Edge.- The leading edge of the stage 1 turbine rotor blades is the area forward of the gill holes. Cracks in the leading edge can be caused by DOD impact (combustion liner pieces) or thermal stress. An indication on the leading edge open enough to show depth is defined as a crack. Some conditions may mislead you in the determination of the presence of cracks. Dirt and debris buildup inlayers on the leading edge, as shown in figure 2-26, are not cracks. When this buildup begins to flake off, the edge of the area where the flake came off causes visible lines. These lines are irregular and appear to be cracks. The other common point of cofusion on leading edge cracks is on the convex side of the leading edge tip area. This area is subject to "scratching" by the small pieces of combustor metal that pass through the HP turbine.

Cracks in the Trailing Edge.- The trailing edge is the flat surface with cooling holes that forms the after edge of the blade airfoil. Trailing edge cracks are difficult to see, but if a crack is suspected, use probe No. 1 for increased magnification. Record the location relative to a cooling hole and the magnitude of the crack. Record any plugged trailing edge cooling holes.

Cracks in Concave and Convex Surfaces.- The airfoil surfaces are the areas aft of the gill holes back to the trailing edge. The tip area is further restricted to that area above the tip cap. When you evaluate the airfoil serviceability, do not consider the tip as a part of that area. Cracks in the airfoil surfaces are very tight, but can readily be seen with probe No. 2. Airfoil surface cracks are irregular in edge appearance and are not usually confined with streaks, which are usually straight in appearance. Record the area by the percent of span or gill hole spacing equivalent for location and magnitude of the cracking. For axial position, use an estimate of percent chord and the position relative to the tip cooling film cooling holes.

Cooling Hole Blockage.- The HP turbine rotor stage 1 blades are film cooled by air that flows out of the cooling holes. Report plugged holes relative to the number of blades affected and the position and number of plugged holes. Ensure the correct callout of the holes (such as the nose cooling, convex gill, tip film cooling holes, and so forth.)