RAIL chiefs are investigating how a block of ice bigger than a car derailed a passenger train in a tunnel.
The Rail Accident Investigation Branch is looking into why the 00.38 First Pennine Express train from Manchester Airport to York came off the tracks in Summit Tunnel, Todmorden, on Tuesday December 28 last year.
The train had been travelling at 70mph when it hit ice, sending the first of its three carriages crashing into the tunnel wall.
Forty-five passengers and two crew members were left stranded in the tunnel for almost four hours.
Fire crews from across Calderdale, Lancashire and Greater Manchester were called to the scene near Bottomley Road, Walsden.
The passengers, many of them returning holiday makers, were eventually walked out of the tunnel in small groups by fire crew members.
Investigators will try to discover why the chunk of ice, which measured eight metres by two metres even after impact, was able to form and then fall from an air ventilation shaft and block the track.
As the train ground to a halt in the tunnel, more blocks of ice fell from above, causing damage to a cab windscreen, a coupler, bodywork and under-frame.
Amazingly, nobody was seriously hurt.
The 00.38, which had been re-routed to that line because of track work elsewhere, was the final train on the line that evening.
The RAIB's investigation will include a review of Network Rail's arrangements for the identification of ice related hazards in tunnels and the steps taken to reduce the risk of a future blockage.
It is independent of any investigations by the British Transport Police and the safety authority.