Page:CAB Accident Report, Pan Am Flight 4.pdf/6

- 6 - The combustion chamber cases were intact but buckled in toward the top. The combustion chambers were in satisfactory condition except that the top chambers were collapsed in the rear. The turbine nozzle inner case was crushed inward through the top 90-degree segment. There was no evidence of overtemperature in the first stage nozzle guide vanes. The high pressure turbine shaft was fractured circumferentially through the forward breather holes to the forward spline rear fillet.

The first stage turbine disk was still intact and attached to the shaft. The disk was rubbed on the inner bore, the front web and rim, and the rear rim. A 90-degree segment of the first stage turbine blades, severely bent opposite to rotation and lacking tip shrouds, was heavily rubbed and notched on the leading edge. Twenty-four blades were missing and the remainder were broken off above the platform. The low pressure compressor turbine drive shaft was slightly bent approximately 17 inches from the forward end and circumferentially rubbed in the planes of the high pressure turbine shaft lockout, the No. 5 bearing, and the first stage turbine disk.

The front and rear face of the outer rail of the second stage inner sealing ring assembly was heavily rubbed and partially crushed. The second stage nozzle guide vanes were severely damaged along the trailing edges with no evidence of overtemperature.

The second stage turbine disk was intact except that half the rear mount flange was broken off. The tip shrouds were missing from all the blades and the fractures varied along the span of the blades. The front rim of the disk and leading edges of the blades were heavily rubbed.

The third stage turbine disk, installed new at the last overhaul, was notched 0.020 inch deep into the front web in the circumferential plane of the stationary third stage inner sealing ring. Apart from the missing web rim segment the remainder of the disk was intact, with faces randomly rubbed and the tie rod holes slightly distended. The third to fourth stage spacer was axially split at a radial buckle and tie rod holes were distended and cracked. The fourth stage inner seal was intact with the rims severely distorted and the knife edges heavily rubbed. The fourth stage turbine disk was intact with slight rubbing on the rear web and rim. The blades were bent axially forward and opposite to rotation. The shrouds were missing as were nine of the blades and the leading edges of the blades were notched.

The third stage inner seal was axially and circumferentially split between the forward flange and the first knife edge, which was unrubbed, and partially split aft of the rear knife edge. The third stage inner sealing ring assembly, installed new at the last assembly, was distorted into three damaged pieces with the inner sealing ring separated from the support through the rivets. The outer rails of the support showed normal guide vane patterns and no abnormal wear was found. The inner sealing ring was torn apart, severely distorted and gouged. The complete rear lip was particularly damaged and showed evidence of an overtemperature condition. Several small sections of the edge of the lip that were not obliterated did not display visible evidence of wear.

The third stage guide vanes were damaged mostly on the trailing edges with no evidence of overtemperature. The vane outer feet were bent outward and worn 0.008