The Regina Cargo Airlines flight originated at Teterboro for Detroit via Fort Mayne. A VFR plan was filed prior to takeoff. The aircraft had been fueled to a total of 1171 gallons, and the cargo consisted of 631 individual packages totaling 13,666 pounds. Upon departure, the aircrafts gross weight was 50,076 pounds as against the maximum allowable gross weight of 45,000 pounds. At 17:27 the aircraft was cleared to runway 19 for takeoff. The engines were run up to a manifold pressure of 15 inches of mercury and ignition was checked on both magnetos of each engine. Takeoff was then started and the manifold pressure was increased to 52 inches of mercury. Puffs of black smoke eminated from the left engine immediately after the takeoff. At an altitude estimated as 200-300 feet, the left engine started to misfire. The landing gear had been raised and was checked for position. The left engine continued misfiring and shortly became worse. The left propeller as feathered. Ahead, the terrain as flat, unobstructed and marshy. Full power was maintained on the right engine and a left turn was started as if to return to the airport. At this point the altitude was estimated to be 400-500 feet. During the turn the air speed fell to 85-90 mph and the aircraft settled. This turning and settling continued until the aircraft neared the ground, when it was leveled laterally. It struck while about level, both laterally and longitudinally, and slid along the ground in a generally northeasterly direction for some 620 feet where it struck some large trees and turned to the left about 180 degrees. Both captain and copilot were thrown clear of the wreckage. PROBABLE CAUSE: “The Board determines that the probable cause of the accident was overloading of the aircraft due to faulty loading and dispatch procedures coupled with engine malfunctioning due to inadequate maintenance.”