Suninmyeyes - I have experience of exactly this problem a few years back in Sharjah with a 747 freighter. Number 4 hydraulic system lost all fluid due to a fractured flexible line.The gear was free falled but the greased plate that allows the wheel to slide down it sheared off - I suspect due to the impact of the gear coming down undamped with lack of fluid.the greased plate assembly is linked to the doors and is supposed to push the doors inboard to clear the gear. With the plate sheared the wheel sat on top of the outboard door with no way of being moved - a successful landing was made as with the Virgin aircraft. If you look at the photographs of the Virgin aircraft you can see that the wing gear doors are open - they should normally close after gear is down,this indicates that the free fall system was operated. This incident brings to 3 the number of times I have known this to happen. I suspect that the gear came up and locked,fluid was then lost and the crew decided to return - that was when the gear hung up after operating the free fall.