(Bloomberg) The US military is grounding its entire fleet of Osprey aircraft to investigate a possible equipment problem that may have caused a deadly crash in Japan, which has raised concern about the safety of the tilt-rotor aircraft that has been involved in several fatal accidents.Most Read from BloombergApple Readies New iPads and M3 MacBook Air to Combat Sales SlumpElon Musk's SpaceX Valued at $175 Billion or More in Tender OfferGlobal Bonds Power Ahead as Dovish Bets Take Hold: Markets