I do not have any idea about how a nuclear bomb works, but suppose an aeroplane carrying a nuclear weapon crashes down to a city. What would be the chance of a nuclear blast ?
I'm no expert but there would not be a nuclear "blast" from my understanding. I think the damage from the radiation would be limited to the crash zone and where the wind takes the airborne particles. You have to be pretty deliberate to have a fission reaction occur and the "bombs" or "missles" hitting the ground would not create the fission required. They are not designed that way. Here is the wiki on nuclear weapons: http://en.wikipedia.org/wiki/Nuclear_delivery And just for fun, here is the wiki on natural occuring nuclear fission: http://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor