CENTRIFUGAL FORCE

Dominion, Volume 31, Issue 252, 21 July 1938, Page 8

CENTRIFUGAL FORCE

Cause of Locomotive Overturning

EVIDENCE ON SPEED REVIEWED “The preponderance of evidence establishes that the cause of the accident as the operation of centrifugal force at sharp curves, which caused the locomotive to overturn. The derailing of the engine was only an incident of the overturning, and was not the primary cause of the accident,” said the Board of Inquiry, set up to investigate the Ratana railway disaster on March 26, in its report to the Minister of Railways.

Reviewing-evidence submitted at the inquiry, the board stated that there was nothing in the recorded times of “W4,” the excursion train, to indicate that, though time was lost and made up at different stages of the journey, the maximum authorised speeds were at any time exceeded on the journey from Wellington to Turakina. The running times scheduled for “W4” were somewhat easier than those for the New Plymouth express, except between Palmerston North and Feilding, 'where the running times were the same, and between Feilding and Marton, where “W4” was allowed 36 minutes, as against 38 minutes for the express. “The possible causes of the accident may ibe grouped under six heads,” said the board. “(1) Defect in track. (2) Obstruction on track. (3) Operating factors. (4) Defect in engine. (5) Defect in rolling stock. (6) Excessive speed.”

No Trace of Obstruction. The board was satisfied that the condition of the track in no way caused or contributed to the accident. The possibility of an obstruction could not be absolutely ruled out, but against this possibility weight had to be given to the following considerations: An examination of the records of cases in which a locomotive travelling at a moderate speed struck an obstruction ou the line showed that the result was a simple derailment of two or more bogie wheels without causing the engine to overturn or even leave the track. “Unless the obstruction was very large and heavy,” said the board, “the locomotive would be unlikely to overturn. In the present case a careful search was made among the wreckage or debris, but no trace was disclosed of any obstacle that could have overturned a locomotive.

“A southbound goods train passed over the curve within half an hour of derailment and negotiated the curve without any difficulty. It is extremely unlikely that any maliciously disposed person would have chosen that particular half-hour —about 2 a.m.—to place an obstruction on the line. Further, the accident occurred at the spot at which one would have expected it to happen if the cause were excessive speed. Even if an obstruction bad been placed on the track and had caused a derailment the results would not -have been wffiat they were in the absence of a contributing factor as high speed. We are, therefore, of the opinion that the accident was not caused by, or contributed to by the presence of an obstacle on the track. Operating Factors. “Engine-driver I’ercival had not driven over the Marton-Wanganui section for about eight years,” said the board, referring to operating factors. “At that time he had made four trips as driver of a night train that ran between Wellington and New Plymouth. He states, however, that be had no hesitation in accepting the assignment of train ‘W4,’ and that he was confident that his knowledge of the track was sufficient. He was supplied with a copy of the working time-table, which indicated the points between which speedlimits and speed-restrictions operated. A number of experienced drivers agreed that when a driver had driven on a few occasions over a section of track he was able to remember that section for an indefinite number of years afterwards.

“The practice of the department is to permit without hesitation a driver io decline an assignment it he considers that he is not sufficiently familiar with the section of line over which the train is to run. It was admitted by Driver Percival and the other drivers who gave evidence that it was not held against a driver in any way if he declined an assignment on the ground that he was not familiar with a section of the line. The driver -’iad had a time relief of twenty-four hours before be commenced duty on the night of

March 25. So far as the time-table for ‘W4’ is concerned, we are satisfied that it could be maintained without it being necessary at any point to exceed- the authorised speeds set out in the working timetable.”

The evidence concerning speed, the report added, could be dealt with under four heads: (a) Evidence regarding t-he time of the accident; (b) the evidence of the passengers and the guard; (c) the evidence of the driver; (d) the condition of the wreck and the relative positions of the vehicles as ascertained after they had come to rest. So far as the time of the accident -was concerned the board considered that in view of the circumstances all evidence given by witnesses on this point must be disregarded.

“There is a good deal of conflict of evidence among the passengers as to the running of the train all the way from Wellington,” said the board, “but in our judgment, nothing was disclosed wfliich indicated that the train at any point between Wellington and Ratana was driven otherwise than as an express train would normally be driven. In this connection it is noteworthy that many of the passengers who spoke of swaying and discomfort were occupying seats over the wheels, or were sitting on the arms of seats, whereas other passengers who were seated near the centre of a car experienced no sensation of swaying or discomfort.” Tecluiical Evidence. After reviewing in detail technical evidence submitted by Mr. A. S. Wansbrough, designing engineer, maintenance branch, New Zealand Railways, as to the position of the locomotive and rolling stock after the accident, the board said that neither the progress of the engine and the first car or that of the rest of train, in the circumstances respectively applying, would have been possible except with an initial speed in excess of 50 miles per hour.

“In respect of the particular question of the overturning speed of the Ab engine,” said the board in a later stage of its report, “the detailed computation based on the actual characteristics of the engine was naturally provided by the designing engineer in the mechanical branch. Mr. Gard’s estimate of the speed at which the locomotive concerned would overturn as being approximately fifty miles per hour on a 6.4 chains curve has been reached by following established principles, is based on adequate data in respect of the design and the sprung and unsprung weights of the engine, and can be accepted as substantially correct. ...

"We have applied degrees of retardation varying, in accordance with the continually increasing obstacles of progression between that due to emergency braking on rails and that duo to the maximum retarding effect probable (this latter acting only for the last second or less). The result is we see no reason to consider excessive the speed estimate of 50 miles an hour arrived at by Mr. A. S. Wansbrough, designing engineer, chief engineer’s branch, for the train on entering the curve; in fact, we lean rather toward the view that the speed was even higher.”