Signalling fault caused Dalwhinnie HST derailment
THE derailment of a Scotrail HST set at Dalwhinnie in the early hours of April 10 was caused by a signalling fault, an RAIB statement concludes. The five-car set, known as HA19, was being operated as an overnight test train between Perth and Tomatin, using power cars Nos. 43012 and 43015 to check stepping distances, so there were no passengers on board; just five crew, who were uninjured. The train had left Perth at 23.10, and was booked to call at all stations in each direction, arriving at Tomatin at 02.08. It was returning south on time at 02.12 and running some 50 mins early on its way back to Perth when the derailment of a bogie on the last trailer and both on the rear power car took place. It occurred on a crossover at the south end of the Dalwhinnie station limits at around 03.03. RAIB says the HST was wrongly diverted from the up line to the down line, and was travelling at 33mph. The crossover speed is 15mph. RAIB adds the signal on the approach to the crossover was displaying a proceed indication for the up line, and there is no signalled route over the crossover to the down line. Both sets of points forming the crossover were detected as being in the correct position for the up line route by the signalling system and were indicated as such to the signaller, even though the points at the north end of the crossover (the end nearest Dalwhinnie station) were set in a position to divert the train onto the crossover. The investigation will also consider these areas:
■ Why the signalling system did not detect that the points were in an incorrect position, thereby allowing the signal to be cleared for the movement along the up line.
■ How the points were able to move as the train passed over.
■ Factors associated with the installation, testing and maintenance of the point machines that operated the crossover. With the train blocking both lines, services between Pitlochry and Aviemore were suspended with a rail replacement coach service. Recovery crews got the HST back onto the rails once RAIB investigations concluded, with the set permitted to return to Haymarket depot at 25mph on April 18. Because of damage to the track and pointwork, Network Rail teams installed plain trackwork in order to reopen the line by April 15, and may replace the points at a later stage.