Page:CAB Accident Report, Pan Am Flight 4.pdf/5

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The engine components that separated from the aircraft were recovered from an area beginning 1.5 miles from the departure end of runway 28L, to 1.8 miles from the runway end. The wing components that separated from the aircraft were recovered from an area beginning 1.5 miles from the end of the runway to a point 8.1 miles from the runway.

Parts of the No. 4 engine turbine case, the third stage turbine disk, turbine blades, guide vanes and a piece of gap cover were found 1.5 miles from the end of the runway. The fourth stage turbine disk and blade assembly with hub attached were found 1.7 miles from the runway. Nearby was the aft reverser sleeve. Next, at 1.8 miles was the main portion of the engine, the forward part of the No. 4 strut, turbocompressor, and part of the cowling including the entire nose cowl.

Three miles from the end of the runway were two outboard aileron balance panel access covers. One-half mile farther, at 3.5 miles was the major portion of the right outer wing panel. At 3.7 and 3.9 miles were two more outboard aileron balance panel access covers. At 5.0 miles was the largest piece of lower wing skin (Sta. 866-948) with a 12-inch section of the aft spar bottom chord and web. From 6.2 to 8.1 miles were scattered pieces of burned lower wing structure.

The right outer wing panel separated near wing station 748 through the inboard end of the reserve fuel tank. The wing inboard of the fracture received only minor mechanical damage while the separated panel was extensively damaged.

The front spar separated at station 748. This fracture and those of the forward upper stringers were generally sharp, with 45-degree edges, and had the appearance of tensile failure. The rear spar and upper rear stringers were bent, twisted, and cracked spanwise in places. The rear spar was fractured at station 779 and its bottom chord was bent up and aft and was twisted clockwise, looking outboard.

The entire skin panel over the reserve tank was buckled upward from its normal position, with a maximum deflection of five inches. Every interspar rib between the tank ends was buckled up and outboard, and the rib-to-bottom stringer connections were all failed.

The fuel shutoff valve for the No. 4 engine was found in the closed position. It was bench-checked and operated properly without leaks.

On inspection of the recovered engine it was found that the fan inlet case had separated from the fan exhaust case. The fourth stage of the front compressor through to the turbine nozzle case remained together as an assembly. The rear thrust reverser remained attached to the exhaust case which had separated from the engine at the exhaust case front flange. The front compressor case and stages were generally bent and crushed at the top.

The rear compressor rotor was intact. In general, there was evidence of stator assembly rub from the tenth through the fifteenth stages. The rear compressor case was generally in satisfactory condition although dented.