Electra N121US was operating on Northwest Flight 710 from Minneapolis (MSP) to Chicago (MDW) and Miami (MIA). The flight departed Minneapolis at 12:51 and arrived at Midway at 13:55. During the short time the aircraft was on the ground at Chicago, approximately 30 minutes, it was refueled and prepared for continuation of the flight to Miami. The flight departed Chicago at 14:38. At 14:45, the flight reported to the Indianapolis, Indiana, ARTC Center over Milford at 18,000 feet and estimating Scotland, Indiana, at 15:12. At 15:13, Flight 710 reported over Scotland maintaining 18,000 feet and estimating Bowling Green, Kentucky, at 15:35. This was the last radio contact with the flight.
At 15:25 the the outboard engines and engine support structures, the complete right wing, and the outer portions of the left wing and ailerons separated in flight. The aircraft crashed out of control.