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 has been shut down because of defects and the unit is continued in service a distinctive tag giving reason for shut down shall be conspicuously attached near the engine starting control and shall remain attached until repairs have been made."

The CFR does not contain any requirements for the maintenance or operation of traction motors or other component; parts of a loco- motive unit. Condemning limits and design requirements, however, are required. for some parts or areas. The AAR has not established standards nor recommended practices for main- tenance or operation. of these parts, but has instead depended on each railroad to make rules to govern its individual needs

III. ANALYSIS

A. The Derailment of Train No. 1

When the armature on the traction motor seized, the direct connection between the pinion gear on the armature and the ring gear-on the axle caused the wheels to stop turning. The friction between the sliding wheels and the rail soon wore away the tread of the wheels at the point of contact. The absence of other ﬂat spots on these wheels indicates that once the wheels began to slide, they remained in a fixed position.

The marks found on heel blocks and frogs at Mason indicate that the wheels had been sliding long enough to increase the flange height to more than 1-11/16 inches, the distance of the heel block below the running surface of the rail. Considering the amount of wear at Mason, it is not unreasonable to theorize that the wheels seized when the train stopped at Effingham, 12.3 miles north of Mason Experience with sliding locomotive wheels and seized traction motors implies that the seizure generally occurs when the locomotive is standing and seldom during movement.

From Mason south to the accident point, evidence of contact between the wheel flanges and the track structure became more prevalent and more pronounced As the head of the rail wore into the sliding wheel, a false flange was produced on the outside edge of the wheel tread, as was shown in Figure 7. The false flange, once started, eliminated any lateral movement of the wheel and thus the wear between the wheel and the rail was concentrated in one groove, which gave more definition to the false flange. The first mark of contact of the false flange with the track structure was on the frog of a crossover at Edgewood, 14.4 miles north of the accident point.

These marks provided conclusive evidence that the wheels were sliding on unit 4031 when the train passed Edgewood. The Operator did not detect the sliding wheels, nor did the crew of the freight train that passed train No 1 in the vicinity of Edgewood. The amount of smoke and sparks produced by the sliding wheels would not have been excessive and could have mixed with the dust produced by the train moving at its permitted speed of 100 miles per hour.

The trailing-point crossover switch in the Southward track at Tonti required the left-hand wheels to make a transition from the switch point to the stock rail as the train moved southward. The sliding wheel could not make the transition because of the height of the false flange.

As the sliding wheel moved off the end of the switch point, the outside of the wheel continued to push the stock rail outward, increasing the gage sufficiently to allow the wheel to drop inside of the rail These and the following wheels of the locomotive derailed and pushed both rails outward. When the locomotive's derailed wheels reached the siding switch, they were diverted toward the siding. The sudden change of direction probably caused the first two units to turn over on their right sides. The destruction of the main tracks and siding south of the turnout began when the derailed locomotive struck the turnout of the siding.

B. The Failure of the Armature Bearings

Although the investigation disclosed that the armature bearings were installed to the