Read this edition's RAIB report brief.
South of Dalwhinnie, on the Highland Main Line, the lines to Blair Atholl are still controlled from a manual signal box. Just before 03:00 on 10 April 2021, an HST being used to check stepping heights and platform edge gaps departed and derailed on a crossover. There were no reported injuries, but the consequences could so easily have been worse.
The signaller had checked the crossover was set for the main line and got the correct indications in the box. However, it had only been possible to clear the protecting signal because of a wiring error made when the point machine at the trailing end was replaced nine months before. When the leading power car forced the points apart at the trailing end, the system detected that the crossover wasn’t set correctly.
This automatically re-sent a command for both point ends to move to the position the signaller had wanted. And so they did…under the train, causing it to come off. The replacement point machine was of a design no longer made and, on the Highland Main Line, only installed between Dalwhinnie and Inverness. RAIB found two conductors inside, which are needed to drive a set of points in a single-ended arrangement, like a siding. For a crossover, they needed to be removed. The local signalling maintenance team didn’t know this, and their checks and wire counting didn’t identify the discrepancy.
RAIB found a lack of clarity in Network Rail’s signalling maintenance standards, but Chief Inspector Andrew Hall also saw a link with the past: ‘Some of the causes of the accident at Dalwhinnie,’ he said, ‘bear an alarming similarity to those found in the multi-fatal accident at Clapham Junction in 1988.’
RAIB found a lack of clarity in Network Rail’s signalling maintenance standards, but Chief Inspector Andrew Hall also saw a link with the past.
The Clapham accident – which led to the deaths of 35 people – was caused in part by fatigue. The signalling technician in that case only had one day off in almost 13 solid weeks of work. RAIB found that the maintenance tester at Dalwhinnie had needed to self-isolate as he had Covid-19 symptoms. His section manager knew but didn’t know that the tester later started to suffer from general tiredness, memory loss and concentration issues. In short, the tester thought he was coping.
The long-term effects of Covid are yet to be fully understood, but it’s clear that it will impact on the fatigue question the industry has been trying to answer since Clapham. To find out more, search ‘fatigue’ on the RSSB’s website, www.rssb.co.uk
To read RAIB’s full report, including the recommendations it made, search on ‘RAIB Dalwhinnie’ in your chosen search engine. To read about RAIB’s investigation into a wrongside failure at Wingfield, search on ‘RAIB Wingfield’.
