TOKYO (Reuters) - A U.S. Navy said it has called off a search for three sailors missing since a transport plane crashed in the Philippines Sea south of Japan on Wednesday enroute to the USS Ronald Reagan aircraft carrier.  During the course of two days, eight U.S. Navy and Japan Maritime Defence Force ships, three helicopter squadrons and maritime patrol aircraft covered nearly 1,000 square nautical miles,  the U.S. Seventh Fleet said in a press release.  Eight other people on a C-2 Greyhound were rescued shortly after the aircraft crashed and transferred to the Reagan.  The latest Navy accident in the Asia Pacific comes after two deadly incidents in the region involving U.S. warships that have raised questions about training and the pace of Navy operations in the region, prompting a Congressional hearing and the removal of a number of some senior officers. The propeller powered C-2 on Wednesday was conducting a routine flight carrying passengers and cargo from Marine Corps Air Station Iwakuni in Japan to the carrier.  The mainstay transport aircraft for the U.S. carrier fleet has been in operation for more than five decades and is due to be replaced by a long-range version of the tilt-rotor Osprey aircraft. The U.S. Navy said it is investigating the cause of the crash. Japanese Minister of Defence Itsunori Onodera told reporters on Wednesday that the U.S. Navy informed him that the crash may have been a result of engine trouble. 