皇冠体育app

1. Important safety messages

2. Summary of the accident

At around 22:15 hrs on 29 October 2018, a rail head treatment train (RHTT) comprising a Class 67 locomotive and two specialised wagons, operated by DB Cargo and travelling between Inverness and Perth, derailed just after passing Dunkeld and Birnam station. Both wheelsets of the 4th bogie in the train derailed at a set of trailing points, ran for around 100 metres causing significant track damage, and then rerailed at the next set of trailing points. 皇冠体育app train then continued a further 15 miles to Perth.

3. Cause of the accident

皇冠体育app RHTT was crewed by a driver, and an operative who operated the rail head treatment equipment in accordance with a pre-defined plan. At some point in the journey, the leading wheelset of the 4th bogie (the trailing bogie of the leading wagon) began to slide rather than rotate, resulting in the creation of a large wheel flat on both its wheels. As the train progressed on its journey, these flats developed, wearing a groove into the wheel treads and creating features on the outside edges of the wheels called 鈥榝alse flanges鈥�.

As the flatted wheelset passed over number 13 points, just south of Dunkeld and Birnam station, the false flange on the left wheel engaged with the converging switch and stock rails. Rather than the wheel tread transferring from the switch rail to the stock rail in the normal way, the false flange on the left-hand wheel became trapped between the stock and switch rail. This caused the outside face of the wheel to run along the gauge face of the stock rail, while the right-hand wheel was pushed up against the opposite stock rail. This led to the wheelset pushing the rails apart, resulting in high lateral forces on the stock rails which in turn overloaded the rail fastenings and in some places the wooden sleepers.

This directly led to derailment of the leading wheelset of the 4th bogie, shortly followed by derailment of the bogie鈥檚 trailing wheelset. 皇冠体育appy ran derailed for approximately 100 metres, before rerailing at 16 points, the next converging set of points. 皇冠体育app derailment caused extensive track damage through this section, including broken rails, which resulted in a signalling fault.

皇冠体育app signaller at Dunkeld signal box heard loud noises as the train derailed and contacted the train driver by radio. 皇冠体育app driver reported to the signaller that he heard a rumble and experienced a reduction of speed. However, because the train had rerailed, its behaviour had returned to normal. 皇冠体育app driver believed he had run over some sand on the track and confirmed to the signaller that he was able to continue. Due to the noise, and the signalling fault, the signaller decided to visually inspect the track in person, rather than caution the next train. Upon discovering the track damage, he blocked the line and contacted the route control office, by which time the RHTT had arrived in Perth. 皇冠体育app signaller at Perth spoke to the route control office, then informed the driver of the RHTT about the track damage at Dunkeld and that the train would not be permitted to continue further.

皇冠体育app RHTT fleet is deployed during the autumn leaf-fall season to combat low adhesion conditions caused by leaves on the line. This is done through a combination of cleaning of the rail head with high pressure water, and application of an adhesion modifier. 皇冠体育app RHTT involved in this derailment consisted of a Class 67 locomotive and two FEA F wagons specifically built to carry the rail head treatment equipment. 皇冠体育app first wagon in the direction of travel included two high pressure water jets positioned immediately behind the leading bogie. Each wagon carries three modules that can be selected to suit the tasks of the train at any particular time, including a generator and pumping equipment, water tanks and/or adhesion modifier tanks.

Each wagon wheel has a single brake block. When the train brakes are applied, the geometry of mechanical links in the brake system cause the brake blocks on the wheels closest to the centre of the wagon (the inboard wheels) to touch first, closely followed by the brake blocks against the outboard wheels. Each wagon also has a mechanical handbrake which applies the brake blocks to one of the wagon鈥檚 bogie. 皇冠体育app handbrake is activated and released by turning a wheel.

Wheel flats occur when a train鈥檚 wheels slide along the rail instead of rotating. This can be caused by the brakes failing to release when commanded to; a handbrake being left on; brakes being applied too heavily; or the train braking normally in an area of low adhesion.

In order to mitigate against a handbrake being left on, the RHTT wagons are fitted with a handbrake interlock system. If the handbrake has been applied, the train鈥檚 brake pipe will not be allowed to pressurise and the train brake cannot be released. Escaping air from the brake pipe is usually audible to train preparation staff in this situation.

It is normal practice in freight yards, for train preparers to carry out a 鈥榬oll-by鈥� test when a freight train leaves the yard in order to check that all the train鈥檚 wheels are freely rotating. However, DB Cargo鈥檚 instructions for dispatching the RHTT from Inverness Millburn yard did not include a roll-by test. 皇冠体育app operative of the RHTT, who prepared the train before the journey to Perth, reported to the RAIB that he checked the handbrakes but he did not undertake a roll-by test. He believed that both wagons were fitted with a working handbrake interlock which should have prevented the train from moving if a handbrake had been left on.

When the RHTT wagons were inspected after the derailment, the handbrake interlock on the first wagon had been isolated. 皇冠体育app RAIB has not been able to identify why the handbrake interlock had been isolated, or by whom. 皇冠体育app operative who prepared the train reported to the RAIB that he was not aware the handbrake interlock had been isolated. 皇冠体育appre was no card or other sign on the affected wagon to warn about the isolation. According to records provided to the RAIB, a rolling stock technician had also examined the RHTT earlier that day and signed off the handbrakes, amongst other equipment, as being fit for service. Because the handbrake interlock was isolated, there was nothing to stop the driver driving the RHTT with the handbrake accidentally left fully or partially applied.

It has not been possible to confirm the exact status of the handbrake during the journey. 皇冠体育app brake blocks associated with the wheels which had the large flats showed signs of excessive heat being generated, consistent with the brake blocks rubbing against the wheels for a significant period of time. However, the other wheelset on the same bogie did not exhibit any wheel flats or heat marks indicating that its brake blocks had not been rubbing against the wheels and that the handbrake was not fully applied on this bogie. Although the RHTT operative stated that he performed handbrake checks, the condition of the inboard brake blocks indicates that they were rubbing against the wheels. If this was the case, the inboard wheels would have been susceptible to wheel flats in low adhesion conditions.

皇冠体育app operative of the RHTT stated to RAIB that the last time he had used the handbrakes was during a short run to Moy the day before. On that trip he reported that he had only applied the handbrake on the other wagon while at Moy and removed it for the return journey. He reported that he did not operate the handbrakes on the wagons after the journey on the previous day. He also reported that, other than to check the handbrakes were off prior to departure, he did not operate the handbrakes at the start of the journey to Perth.

皇冠体育app nature of the RHTT鈥檚 daily work, and the conditions it operates in, means that it regularly experiences very low adhesion conditions. Evidence from Network Rail鈥檚 engineers responsible for the RHTT fleet indicates that wheel flats are common on RHTTs, and that wheels are routinely changed once or twice during the leaf-fall season, which usually lasts from early October to early December each year. 皇冠体育app wheelsets either side of the water jets (the two inboard wheelsets on the wagon) are considered the most susceptible to wheel flats as they are exposed to airborne water and jetting debris, and pass over a saturated rail during rail treatment operations.

4. Previous similar occurrences

皇冠体育appre are significant similarities between this accident and a derailment at Hatherley, near Cheltenham Spa, on 18 October 2005 (). That derailment was caused by false flanges forming on one of the wagon鈥檚 wheelsets. 皇冠体育app wagon ran derailed for around four miles, causing extensive track damage and partially blocking the line for eight days. 皇冠体育app false flanges on the derailed wheel had been caused by the wheelset being dragged from its origin at Bescot Yard, with its handbrake applied. 皇冠体育app applied handbrake and the dragging wheelset were not detected during the preparation, dispatch or journey of the train. 皇冠体育app wagon was not fitted with a handbrake interlock. 皇冠体育app RAIB made recommendations relating to handbrakes checks, and the effectiveness and availability of roll-by examinations.

On 5 January 2006, large wheel flats developed on a freight train travelling from Meldon Quarry, Devon (). 皇冠体育appse flats caused high impact loads to be exerted on the track, resulting in a broken rail at Urchfont, Wiltshire, and two further broken rails at Kennington, near Oxford. 皇冠体育app wheel flats were likely formed by the wheels sliding under low-adhesion conditions on a long descending gradient from Meldon Quarry. No roll-by test was undertaken at the exit from the Meldon Branch line, and the flats were not detected during the subsequent journey. 皇冠体育app wagon involved was fitted with a working handbrake interlock and therefore the flats were not caused by a handbrake being left on. 皇冠体育app RAIB attributed the most likely cause to a combination of the long descents in slippery rail head conditions and a driving style which was not appropriate for those conditions.