Nothing is being produced that can replace the Twin Otter. Everytime a Twin Otter is destroyed, for whatever reason, the price of Twin Otters globally increases. If I knew how to build and produce an aircraft that could perform and be as reliable as the Twin Otter, I would be richer than Bill Gates. The problem is that there is not a huge demand for an aircraft like the Twin Otter, because there is no Vietnam war on, or anything of that nature, where governments such as the US, can afford to order large amounts of these types of aircraft. Hence the Twin Otter is a by product of the Vietnam war.