The line was operated on the time interval system (rather than block working) so that there was no means at Armagh of knowing that the line was not clear. The required 20-minute interval before letting a fast train follow a slow one having elapsed, the following scheduled passenger train had left Armagh. With an engine of similar performance, but a much lighter train (six vehicles), it was managing about up the gradient when, at a distance of about , the driver of the ordinary train saw the approaching runaway vehicle. He braked his train, and had reduced speed to at the moment of collision.