The U.S. military said Wednesday it has temporarily grounded its entire Osprey fleet worldwide after a deadly crash last week off southwestern Japan. The military said a preliminary investigation indicates a “potential material failure” caused the Nov. 29 accident, which killed eight American service members onboard a CV-22 Osprey aircraft. The stand-down of Osprey aircraft of the Air Force, Navy and Marine Corps will provide time and space for a thorough investigation to determine the causal factors and recommendations to ensure the fleet of tilt-rotor aircraft returns to operations, it said….