Investigators were prevented from examining controls and instruments in the driver's cab because of the precarious position of the badly damaged front carriage of the Uckfield-bound train, which is overhanging a 30ft embankment.
A 200-ton crane was brought in, but the location of the crash site down narrow country lanes has delayed the operation. A temporary road has been laid across the fields to the wreckage, in which the body of one victim is still trapped. The other train, which was going to Oxted, is in a more stable position by the track but much of the front carriage was sheared off in the collision.
Human error is one of the options being considered by the inquiry into the crash, just outside Cowden station on the Kent-Sussex border. Both trains were equipped with the standard automatic warning system.
If a driver passes a signal at amber or red this should sound an alarm in the cab and apply the brakes automatically. Drivers can override the system but it registers any override acting like the 'black box' in an aircraft.
However, investigators have been able to start looking at the points and the signalling system controlled from a box at Oxted. The signals also have a recording device which will reveal what colour the lights were when the two trains went on to the single track stretch of line.
There are points at each end of the single track section between Hever and Ashurst but it is possible for a train to go through points set against it without being derailed. It was the train travelling towards Oxted which apparently should not have been on the line.
Three of the crash victims were named last night. Two were passengers, Raymond Pointer, 61, and his wife Maura Ann, 56, of Crowborough, East Sussex. The third was a guard, Jonathan Brett-Andrews, 36, of Caterham, Surrey. The names of both train drivers, who also died, are to be released today.Reuse content