Page:CAB Accident Report, Eastern Air Lines Flight 304.pdf/8

 setting is equivalent to the stabilizer being in the full AND position.

Examination of the drive gear assembly of the stabilizer drive unit revealed normal wear patterns on the planetary gears and the male spline extension which transmits power down to the dual sprocket assembly. In addition, another wear pattern was found 1/4 inch below the normal engagement point of the extension. This abnormal wear pattern continued to the end of the splined shaft. The flanks of the splines in this area were highly polished around the entire periphery of the shaft, indicating the wear occurred over an extended period of time, and could not have occurred during breakup. There was also considerable spalling of the case hardened surface at the end of the splined shaft. The mating female splines, in the top of the dual sprocket assembly portion of the stabilizer drive unit, exhibited a similar severe wear pattern. The wear had produced convex surfaces lengthwise on both flanks and left a lune-shaped area on the crest of each tooth. This damage from misalignment of the mating splines resulted from oscillation of the sprocket assembly since the planetary gears at the top of the shaft had no abnormal wear. The case hardened male splines at the bottom of the shaft did not develop the lune-shaped wear. A bearing seat at the top of the dual sprocket assembly also exhibited the abnormal wear from a 1/4 inch displacement, and oscillation of the assembly. The lower support bushing P/N2652666 for the sprocket shaft, which supports the sprocket assembly in the vertical plane for proper spline engagement and also restrains it in the lateral direction, was not recovered. Other sprocket assemblies used for comparison showed bright polishing on the lower shaft where it fits into the lower bearing support bushing and showed polishing on the bottom sprocket hub where it rests on and is supported by this same bushing. The sprocket and shaft assembly from N8607 showed none of this. The lower support bushing has a flange on its outer circumference and when installed properly (flange up) it overlaps the lower bearing and thus provides the vertical and lateral support for the sprocket shaft assembly. The three rivets attaching the lower sprocket to the assembly sheared circumferentially from loads applied in the ANU direction, but the needle bearings from this sprocket scored the shaft axially as the sprocket and shaft separated.

No portion of the PTC actuator has recovered.

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There was no evidence of in-flight fire.

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The extreme disintegration of the aircraft structure precluded any crash/injury study. The crash was non-survivable.

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The flight maintenance logs fro N8607 were recovered back through May 22, 1960, the date of delivery to EAL. They revealed that on August 20, 1963, the aircraft was subjected to abnormal flight conditions during flight in severe turbulence. A Severe Turbulence Mechanical Check of the aircraft at that time revealed only minor damage. On September 11, 1963, the stabilizer jammed in the full ANU position during a landing at San Juan, Puerto Rico. An inspection at that time revealed that power from the drive unit was not transmitted through