Very similar to the Caledonian Tristar when backtracking 26 for departure decided he would keep to the left hand side of the runway whilst doing so. Unfortunately, the left main gear was on the soft tarmac that was between the grass and the runway edge lights. Luckily there was a vehicle following it down the runway and noticed, so we stopped him from taking off. Not sure what would have happened as the left bogie was covered in soft tarmac!