Page:NTSB Report, Japan Air Lines Flight 813.pdf/10

- 7 - Engine overhaul records showed that during the course of the engine overhaul the low pressure compressor torque ring, P/N 310172, was found cracked and therefore replaced. The torque ring is located in the low pressure compressor at the area of the compressor case "C" flange adjacent to the fourth stage compressor stator assembly. It serves to prevent rotation of the compresesser stators. In position, the ring is tightly fitted. and a series of slots on the ring mate With a series of lugs on the outer diameter of the fourth stage stator shroud. By design the torque ring is secured in place by 90 rivets, P/N AN 13340, made of AMS 1232, a nickel base alloy. The design shear strength of each rivet is 16,000 p.s.i. at 350 degrees, C. The ring is riveted to the compressor case "C" flange.

There are three borescope inspection ports in the outer compressor case and stator outer shroud. Each of the ports is closed by a threaded plug. Though not designed for the purpose, the ports and plugs tend to impede rotation of the compressor stator assembly.

Company maintenance personnel involved in the engine overhaul and installation of the new torque ring stated that's new ring was drawn out of the maintenance parts department. They described how it was fitted into the engine and. that when it was properly in place the necessary rivet holes were drilled in the ring to align with the rivet holes already in the compressor case adjacent to the "C" flange. According to the statements, rivets were pushed into the hole and secured with paper tape. A mechanic then went into the engine case section and riveted the torque ring in place. The mechanics involved stated that the rivets used in the work were not drawn from the stock room, as they