International search continues for endangered 9-year-old boy; likely on sailboat with father (PHOTOS)

SEATTLE -- The FBI and the U.S. Attorney's Office are working together to find a missing, endangered 9-year-old boy.

Authorities believe Billy Hanson's father, 46-year-old Jeffrey Ford Hanson, took the boy and could be sailing toward Mexico or the South Pacific.

The boy was expected to be put on a flight to his mother on Sept. 4, but never showed up to the airport.

The FBI says Hanson is “extremely volatile” and “authorities are gravely concerned about the child’s safety.”

A U.S. District Court judge issued a federal warrant for Hanson's arrest on September 12th. He is charged with international parental kidnapping.

A neighbor told Q13 FOX News that the father is a very experienced sailor and has sailed around the world on his own. He believes the father and boy left the marina on Aug. 28, and the boy’s parents may be in the midst of a custody battle.

Billy is listed as white, 4-feet tall and 90 pounds. He has brown curly hair and brown eyes.  He was last seen wearing no shirt, black knee-length surf shorts and no shoes.

Billy’s father Jeffrey Ford Hanson is a 46-year-old white male, 160 pounds and 5 feet 5 inches. He has blue eyes and blonde hair.

They are believed to be on a white, 1976 Cooper sailboat named Draco. The boat’s licence number is wn6753nz. The Boat has a fiberglass hull and a 6-inch red stripe along the side.

Investigators are asking for anyone with information to call 1-800-CALL-FBI.