The wreckage of TWA Flight 800 is set to be destroyed — nearly 25 years after the doomed aircraft crashed off the coast of Long Island, killing all 230 people on board. For the last two decades, the reconstructed Boeing 747 has been housed in a Virginia hangar and used by the National Transportation Safety Board as a training tool for accident investigators. But the federal agency on Monday announced it planned to decommission and destroy the wreckage, as its lease on the 30,000-square-foot Ashburn warehouse is set to expire.