ANCHORAGE, Alaska (AP) — A team of federal accident investigators is expected to arrive in Alaska Tuesday to try to piece together what caused a deadly midair collision between two sightseeing planes. The passengers were from the cruise ship Royal Princess and were on sightseeing flights.

Four people were killed after the floatplanes carrying cruise ship tourists collided Monday near the southeast Alaska town of Ketchikan, the Coast Guard said. Two others were missing, said Petty Officer Jon-Paul Rios, a Coast Guard spokesman.

A team from the National Transportation Safety Board is expected to arrive in Ketchikan Tuesday afternoon, agency spokesman Peter Knudson said. He said board member Jennifer Homendy also is traveling with the so-called “Go Team,” which investigates major accidents. The floatplanes collided under unknown circumstances, Federal Aviation Administration spokesman Allen Kenitzer said in an email to The Associated Press.

Eleven people were inside Taquan’s single-engine de Havilland Otter DHC-3 when it went down as it returned from Misty Fjords National Monument.

Three people who died were among five people aboard the second plane.

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