TOKYO (Reuters) – A U.S. Navy transport plane carrying 11 people crashed in the Philippine Sea south of Japan on Wednesday as it flew to the aircraft carrier the Ronald Reagan, the U.S. Seventh Fleet said.

Eight people had been rescued, with the remaining three unaccounted for, it said, adding that all of the rescued personnel were transferred to the Ronald Reagan for medical evaluation and were in good condition.

“Search and rescue efforts for three personnel continue with U.S. Navy and Japan Maritime Self-Defense Force (JMSDF) ships and aircraft on scene,” the U.S. Seventh Fleet said in a news release.

“The incident will be investigated.”

The aircraft was conducting a routine transport flight carrying passengers and cargo from Marine Corps Air Station Iwakuni to the carrier, which was operating in the Philippine Sea as part of an exercise with Japanese forces, it said.

Japanese Minister of Defence Itsunori Onodera told reporters the U.S. Navy had informed him that the crash in the Philippine Sea may have been a result of engine trouble.

The propeller powered transport plane, a C-2 Greyhound, carries personnel, mail and other cargo from mainland bases to carriers operating at sea.

C-2 aircraft have been in operation for more than five decades and are due to be replaced by the long-range tilt-rotor Osprey aircraft.

(Reporting by Tim Kelly; Additional reporting by Tetsushi Kajimoto; Editing by Robert Birsel)