Page:CAB Accident Report, American Airlines Flight 1.pdf/13

 the rear in a slackened condition.

The cable, pulley and mounting bracket were removed intact as an assembly and reinstalled in their normal location in another DC-3 aircraft for tests to determine the following information.


 * 1) The forces required at the control column to overcome jamming of the right elevator down cable and pulley,
 * 2) The forces and action necessary to break the pulley flange and force the cable off and into the space between the pulley and bracket,
 * 3) The force necessary at the control column to actuate the cable through the normal travel range after it was lodged between the pulley hub and the mounting bracket fork.

The results of these tests indicated that jamming of the cable and pulley bracket assembly located at the station tested (Fuselage station 623-625), such as occurred in NC 25663, can be overcome by the application of normal force on the control column. Furthermore, it appeared from the tests that this abnormal pulley and cable condition was probably caused by the right end of the tail wheel spindle bulkhead being jammed through the right side of the fuselage during impact, carrying the cable with it under tension, breaking the pulley flange and tearing the mounting bracket from its anchorage.

Also, there were some control cable guide pulleys and mounting brackets normally located under the floor along the fuselage, particularly those located in the center section, which were completely destroyed by fire and were not available for inspection. However, the control cables were inspected at the points where the missing pulleys and brackets would have been located together with those where only the micarta pulley had been consumed by the fire leaving the metal hub and bracket. While the cables indicated heat at these points, there was no evidence in the form of frayed strands or scuffing to indicate that a possible jamming of control cable had occurred. Furthermore, a series of tests was conducted on a similar aircraft to determine the possibility of jamming the elevator controls in the "up" position by objects in the cockpit. These tests failed to reveal any condition under which such jamming might reasonably be expected to occur. In fact, there was no evidence found in the entire control system to indicate that a jamming of any of the controls had occurred.

The various units of the automatic pilot were thoroughly examined. While many parts were severely damaged, it appeared that in all probability the damage had resulted from impact and the subsequent fire. Nothing was found to indicate that any malfunctioning of the automatic pilot had occurred during flight. The servo unit was removed and subjected to tests to determine whether any jamming condition existed in the cylinders. The results of these tests were entirely negative. While it is conceivable that an automatic pilot might become jammed in such manner as to make it impossible for the human pilot to assume control of the airplane, this possibility appears to be extremely remote.

The effect of a failure in the expansion tank assembly of a DC-3 steam heating system was tested by duplicating the steam heating system and surrounding companionways in the cockpit in relation to the captain's and first officer's position and by breaking the water glass and releasing a normal head of steam into the companionway. From this test it appeared quite improbable that any such break could result in a situation that would imperil either crew member, or that either crew member could not easily correct without injury to himself.