SERVICE LIMITS This section discusses the types of damage that you might find when conducting a routine inspection. This material will be limited to a discussion of the major ngine areas. The parts nomenclature that is used in this section is found in figure 2-11, a foldout at the end of this chapter.

Compressor Section You should inspect the compressor section for nicks and dents, cracks, spacer rubs, casing rubs, blade tip rubs, bent edges, missing pieces, and trailing edge erosion. Inspect the first-stage compressor midspan damper for leading edge dents and other types of

Figure 2-10.- Zero indexing the compressor rotor. damage. Beginning with the third stage, if a slight tilting of the blade or raising of the blade platform is observed, suspect blade root failure. This condition requires suspended engine operation until the condition has been evaluated

COMPRESSOR DAMAGE.- In tie following paragraphs, redescribe some of the damage you may find during an engine inspection. You can find the condition codes used to describe engine damage in foldout table 2-1.

Airfoil and Tip Cracks.- Cracks in the compressor hardware are difficult to detect because they are tight and shallow in depth. You can miss these subtle efects because of deteriorated borescope optics or if you rotate the rotor too fast. You should record all crack information relative to the stage, area, magnitude, direction, and adjacent blade condition.

Cracked Dovetail.- A cracked dovetail of a blade may lead to blade loss. The location of the blade will determine the extent of engine damage. Before the actual catastrophic failure of the blade, the separated crack in the dovetail will be evident by a leaning blade platform. You can find this fault by using the borescope to inspect each blade platform. The leaning blade platform will be higher than the adjacent nonleaning blades. e A "leaner" is a blade that has a crack on the aft ide of the dovetail and is leaning in the forward direction (fig. 2-12). If a leaner is detected, it must be verified and the engine should be removed from service.

Airfoil and Tip Tears.- The most critical area of a torn blade is the area around the end of the tear and its location on the airfoil. You should inspect this area for cracks that lead from the tear and are susceptible to propagation. This condition could lead to the loss of the airfoil section that would create downstream impact damage. You should record all information such as stage, blade locations, area of the blade in which the defect was found, and the condition of the rest of the airfoil and adjacent airfoils. Section A of figure 2-11 shows the nomenclature of a blade.

Leading and Trailing Edge Damage.- Random impact damage can be caused throughout the compressor rotor stages by FOD and DOD. The leading and trailing edge of an airfoil is the area of the compressor blade extending from the edge into the irfoil. You must assess both sides or faces of the airfoil when determining the extent of a given defect. If you observe a defect, estimate the percentage of damaged chord length. Observe the defect and the condition of the airfoil area around the defect. If the observed damage is assessed to be "object damage," the most difficult determination is the differentiation between cracks, scratches, and marks made by the passing objects. Cracks are usually tight in the airfoils, but the apex of the damage usually allows viewing into the airfoil thickness. This provides a direct inspection of the area around the crack You may have to use all the probes at varying light levels to determine the extent of the damage.

Tip Curl.- Compressor rotor blade tip curl is a random and infrequent observation. tip curl is usually the result of blade rub on the compressor case. Tip curl also can be the result of objects being thrown to the outer circumferential area of the flow path and then being impacted by the rotating blade tip (either leading or

Figure 2-12.- Compressor blade leaners.

trailing edge). These curled tips are usually smooth in the bend area of the airfoil distortion. However, you should inspect the area at the change in normal airfoil for tears or cracks. When you report tip curl, estimate he percent of the chord length, the number of blades with curl, and the condition of the adjacent airfoil area. Record any evidence of impact and inspect for the origin of the impact. Always look at the adjacent blades for evidence of tip clang.

Missing Metal.- Missing metal from compressor rotor blade airfoils is a result of the progression of cracked or tom airfoils that release part of the airfoil into the flow path. Crack propagation in the root fillet area can result in the separation of the entire blade. Severe FOD or DOD may result in several random rotor and stator airfoils with missing metal. The inspection report hould include the stage, the number of blades with missing metal, the amount, and the location on the airfoil. Estimate the percent of chord, the span of the airfoil that is missing metal, and the condition of the remaining airfoil.