Federal investigators are due in Alaska on Tuesday to try to find out why two sightseeing planes collided in mid-air over open water during daylight hours, killing at least four tourists.
The National Transportation Safety Board investigators are expected to arrive in the southeast Alaska town of Ketchikan, near where Mondays crash happened, during the afternoon, an NTSB official said.
The two aircraft went down over water about 25 to 30 miles (40-48 km) northeast of Ketchikan, according to U.S. Coast Guard Petty Officer Jon-Paul Rios.
Ten other people were injured in the collision, he said.