Question 10Gas Turbine - 1st Asst/Chief

The correct answer is B) The locking lug blades. During a borescope inspection of a GE LM2500 gas turbine compressor, the locking lug blades on each compressor stage are used as a reference for indexing the blades. The locking lugs are designed to prevent the compressor blades from rotating, and their position can be used to identify the orientation of the blades for the inspection. The other options are incorrect because: A) The IGV (Inlet Guide Vane) actuator is not used as a reference for the compressor blades; C) Witness marks on the nozzle and blade are not typically used for this purpose; and D) Scribe marks on the stator and rotor diaphragm are not the primary reference points for indexing the compressor blades during a borescope inspection.