Incident Overview
During a descent, an aircraft experienced a failure of its right engine. The crew performed a shutdown and subsequently landed without further incident.
Failure Mechanism
Investigation revealed that the engine failure originated in the low pressure turbine area. Failed anti-rotation pins allowed gas loads to drive normally stationary third stage vane clusters. The rotation of these clusters in their channel caused them to machine themselves out through the low pressure turbine case.
Pin Failure Details
Evidence indicated that 23 of the 44 third stage vane anti-rotation pins ruptured initially. This was followed by fracture of the remaining pins due to shear overload. The pin stress rupture was determined to be the result of bending stresses on the vane pins from vane twist and pin material creep.
Corrective Action
A design task was initiated in 1986 to develop a more durable pin. In May 1987, Pratt & Whitney released a new material anti-rotation pin, part number 803995 (INCO 901 non-stepped), to replace the previous PN 599714 Tinidur pin.