What action should be taken if a crack is discovered on a turbine disk?

In turbine engine maintenance, the integrity of critical components such as turbine disks is essential for ensuring safe and reliable operation. The discovery of a crack on a turbine disk signifies a potential failure risk, which could lead to catastrophic consequences if not addressed properly.

Rejection of the disk is the most appropriate action in this scenario. The reason this is correct is that cracks in turbine disks compromise their structural integrity and load-bearing capacity. The high-speed rotation of turbine disks under extreme thermal and mechanical stress can exacerbate any existing flaws, leading to fracture or failure during operation.

Replacing or rejecting the damaged part allows for the installation of a new or repaired disk that meets the stringent safety and performance standards required for turbine operations. This preventive action helps ensure that the engine operates safely and effectively, minimizing the likelihood of accidents related to material failure.

Other options, such as attempting repairs or monitoring the crack, are not viable in this case due to the high stakes involved with turbine engine components. Repairing a critically stressed part could introduce further risks, and monitoring a crack does not address the immediate hazard posed by the compromised structure.