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Accident near Didcot, Western Region Involving 70026 Polar Star on November 20 1956

A ten-coach excursion train, 8.30 a.m. rom Treherbert, South Wales, to Paddington, was derailed at about 1.15 p.m. on Sunday, November 20, at Milton, between Steventon and Didcot, after it had been diverted to the up goods loop from the up main line, on which engineering works were in progress. The locomotive, "Britannia" class Pacific No. 70026, Polar Star, went down a 20-ft. embankment with the first four coaches, which were wrecked. Three more coaches were derailed. Ten persons were killed, and 96 persons were taken to hospital. The driver md fireman were not very seriously injured. A11 lines were clear by 8 a.m. next morning, with a speed restriction enforced. All wreckage had been cleared by then from the top of the embankment, but the locomotive was not rerailed until Sunday, December 4. At the opening of the official enquiry into the accident, the driver admitted that he had overlooked notice of the diversion, and was travelling at about 35 m.p.h: He was on a strange engine, with a left-hand drive, and failed to observe two signals at the approach to the loop. The accident is the first since 1942 on the Western Region and its predecessor the Great Western Railway which has involved the death of a passenger.

The Rerailing of Britannia 70026 Polar Star

After the accident at Milton, near Didcot, on November 20 1956, in which "Britannia" class 4-6-2 locomotive No. 70026, Polar Star, plunged down an embankment, the problem of righting the engine was discussed, and Motive Power Superintendent, Western Region, decided that the Maschinenfabrik Deutschland re-railing equipment should be used. This consists of a motorised hydraulic pump unit and a combination of jacks of various types.
Apart from avoiding prolonged occupation of the main line, which would be involved had the locomotive been moved by cranes, the use of this re-railing equipment would serve as a useful exercise for the Bristol Motive Power Breakdown Gang, who had recently been supplied with it, but who had not received any practical experience with the heavy lifting apparatus other than during the demonstration of the gear by the maker's representative. Besides the foregoing considerations, it was thought to be extremely doubtful that the bank would have sufficient strength to support the extension girders of two 45-ton cranes, and there was little doubt that to provide the necessary support the Civil Engineer would have to pile a considerable section of the embankment.

It was arranged that the engine would be righted towards the embankment and taken out through the Ministry of Supply Depot at Milton, over a temporary track, previously laid. In addition, to permit the engine being righted, it was agreed that a section of the embankment should be cut back to a depth of 10 ft. from the flanges of the wheels ; also for a double sleeper platform to be laid, the top surface coinciding with the temporary track.

It was also arranged for flat-bottom rails to be attached to the engine wheels by U-shaped clips. This would ensure that the engine, when righted, could if possible be drawn direct from these rails to the temporary siding. Flat-bottom rails were chosen as it was considered that these would become embedded into the top timbers of the sleeper platform, thereby tending to restrain any transverse movement during the up-righting operation. In addition to this, "U" spikes were driven into the timbers, adjacent to the line of contact with the lower f.b. rail, as a further precaution.

The Motive Power Department representatives decided that the Kelbus hauling gear would be used in conjunction with the Maschinenfabrik Deutschland re-railing equipment. The purpose of using the Kelbus equipment was twofold : to provide a safety precaution during the lift ; and to upright the engine at a pre-determined angle.

The Kelbus gear was to be anchored to the track of the up loopline, on which would stand a 2-8-2 type ("72xx" class) tank engine, and the block attached to a large boiler sling located round the dome of the overturned engine. The rope for the Kelbus block was to be passed over a snatch block, also secured to the far rail of the up loopline, and coupled to a diesel-electric shunting locomotive. It was subsequently estimated that a four-ton pull on the tow rope would provide a sufficient turning moment to right the engine when it had reached approximately 45 deg. to the horizontal.

The engine was lying on its side at the bottom of a steep embankment at an angle of 12 deg. below the horizontal. This called for special lifting attachments to be manufactured, as the dome on the "Britannia" class engine was not of sufficient dimensions to use the lifting beam in conjunction with two 40-ton step jacks. The dome cover was removed and two lengths of 5-in. angle iron secured to the dome face by using the existing studs. In addition, a flanged spigot was manufactured at Bristol, to provide an additional lifting point during the initial lift of the engine and this spigot was secured to the upper pop safety valve seating joint.

The initial lift, taken under the angle irons previously referred to, was made with the two 40-ton step jacks, and the engine was raised, with comparative ease, to the horizontal position. Some concern had been felt in regard to the spongy nature of the ground at the point where the lift had to be made. This was confirmed during the initial lift, for while special timbers had been cut to spread the load over this area, considerable sinking took place and it was necessary to support the engine with sleepers during the subsequent jacking movements.

During the initial lift of the engine to the horizontal, water remaining in the boiler commenced to run out and this caused considerable worsening of the ground conditions immediately below the jacking positions. Subsequent operations were considerably harassed by the presence of water in the vicinity and a considerable amount of packing was, in fact, lost into the ground. In consequence, the up-ending movement towards the angle of 45 deg. was relatively slow, but it did prove the effectiveness of the equipment, and demonstrated the ease with which it could be done when compared with manual hydraulic jacking.

Because of the height of lift which had to be made to permit the attachment, of the rack chains, the step jacks were abandoned, for lifting from the dome, in favour of two 40/20-ton telescopic jacks, provided with loose "V" heads manufactured at the request of the Motive Power Department, Bristol. These appliances were considerably lighter than the step jacks and therefore easier to handle. When the engine had been lifted to 30 deg. to the horizontal (that is, a total angular displacement of 42 deg.) it was possible to attach the rack chains for lifting purposes. These were anchored around the spring hangers at the front end, between the leading and driving coupled wheels, and at the trailing end around the pony truck fulcrum and frame stretcher.

A very substantial base of wagon head stocks and sleepers was then laid to provide ample support and to spread the load over a considerable area. Even then, some subsidence took place, but a firm bed had been made to support the 40-ton step jacks, from which the steps had been removed, and the "V" jack heads inserted. At that point the capabilities of the Maschinenfabrik

Deutschland equipment were amply demonstrated, and very quickly the engine was righted. At an angle some 45-50 deg. to the horizontal, it was apparent that the Kelbus gear could, without undue load being taken by the tow rope, carry out the uprighting of the engine, and the diesel-electric locomotive, which had been special provided because of its steady pull, was allowed to complete the operation.

Having been up-righted, it was necessary for the engine to be traversed away from the embankment, at the trailing end, a distance of approximately 4 ft. 6in. This necessitated the Engineering Department laying a further temporary platform alongside the existing one. Traversing was achieved by using a small re-railing bridge, a traverser and 150/75-ton jack. The "U" clips on the flat bottom rail were first removed and the trailing end traversed about the bogie, which remained resting on the flange of the rails.

The next operation involved lifting the engine bodily by using the 150/75-ton jack at the trailing end and two 40/20-ton jacks at the front end. Ordinary bull head rails, laid on their sides, were then placed under the engine when it was lowered and pulled on to the temporary track, for removal to Didcot shed.

Last Updated : Monday 18th March 2013 08:40

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