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Because Captain Bagus had indicated an elevator control failure, investigation was immediately directed to the longitudinal control system of the aircraft. Upon removal of the yoke assembly access panel, it was immediately noted that the aft or bearing end of the link assembly was not connected to the clevis in the elevator control tall section assembly. (See attachment 1.) The bolt which normally connects the clevis and link assembly was missing.
The effect of this disconnect condition would be the loss of all longitudinal control except that obtained through use of the elevator trim tab system and that which could be obtained by manipulation of engine power. Under this condition the autopilot could not be used for pitch control; however, both the manual control system and the autopilot system could be used normally to furnish lateral and directional control.
During a search of the tail area, a bolt of the same size and specification. AN5-12, as the missing bolt was found. It was found lodged on the right side of a shelf of a bracket in the tail compartment. The shelf where the bolt was found is located aft of and above the link assembly and clevis attachment and separated by a bulkhead containing 3-1/2-inch lightening holes. The bolt did not have a washer, castellated nut, or cotter key on it and no such item which would fit the bolt was recovered.
Examination of the bolt showed it had been in recent use. The shank surface was moderately bright and there was no evidence of rust, corrosion, or grease film on the bolt. The peaks of the threads revealed minor wear and polishing. A small amount of loose residue was found in the cotter key hole. This residue appeared to be the same as residue which was accumulated in the bottom of the fuselage in the area below the link assembly-clevis attachment. Relatively, the shelf where the bolt was found was clean.
At the request of the Board, the recovered bolt, clevis, and link assembly were examined by the National Bureau of Standards. From the examination it was not possible to identify the bolt with the specific link assembly and clevis from N 5140B. It was possible, however, to determine from marks on the bolt that it had been installed in an assembly with the same dimensions as the clevis forks and bearing bore of the link assembly. (See attachment 2-A.)
It is worthy of note that the AN5-12 bolt is not specified for any other attachment or assembly in the empennage section of the C-46.
The units composing the link assembly and clevis attachment (see attachment 2-B) were examined. The aluminum alloy push-pull tube, the fore-and-aft end riveted attachments, the celvis unit, and clevis bolt holes showed no damage. The bearing on the aft end of the tube rotated freely and was undamaged.
Although there was no physical indication that an AN5-12 bolt had connected the bearing end of the link assembly to the clevis at impact, personnel of Associated Airmotive, Inc., insisted it was possible for a bolt to have been properly in place at impact. It was further contended
