On October 10, 1933, a Boeing 247 propliner operated by United Air Lines crashed near Chesterton, Indiana. The transcontinental flight, carrying three crew and four passengers, had originated in Newark, New Jersey, with its final destination in Oakland, California. It had already landed in Cleveland and was headed to its next stop in Chicago when it exploded en route. All aboard died in the crash, which was proven to have been deliberately caused by an on-board explosive device.

More Info: en.wikipedia.org