HOLLAND, Mich. (AP) — Researchers are setting out again in search of the remains of Northwest Airlines Flight 2501 that disappeared over Lake Michigan nearly 70 years ago.

The airplane was carrying 58 people from New York to Seattle when it went missing in 1950. There were no survivors, marking the worst aviation disaster in the U.S. at the time.

The Michigan Shipwreck Research Association has spent years searching for Flight 2501, discovering 10 shipwrecks along the way.

Researchers plan to narrow the search area and use more advanced equipment this spring.

The association has teamed up with Greg Busch, an oceanographer and owner of Busch Marine in Freeland. Busch has a specialized “sonar sled” and a submarine to scour the Great Lakes’ deep waters.

The team launched its search Wednesday. They hope to begin expeditions early next month.