On August 28, 2001, about 1805 eastern daylight time, a Dassault/SUD Fan Jet Falcon, N617GA, piloted by an airline transport pilot rated pilot and commercial rated copilot, sustained substantial damage on impact with terrain and objects during a main wheels up landing on runway 33 (5,090 feet by 100 feet, dry, grooved asphalt) at Detroit City Airport (DET), Detroit, Michigan. The airplane came to rest off the departure end of runway 33. The non-scheduled domestic cargo flight was operating under 14 CFR Part 135. Visual meteorological conditions prevailed at the time of the accident. The flight was on an IFR flight plan. The pilot and copilot reported no injuries. The flight originated from DET and was destined for Greater Rockford Airport, near Rockford, Illinois. The flight declared an emergency and returned to DET for a landing at the time of the accident. The captain stated that after the freight was loaded, he closed the cargo door making sure it was over center. He reported the copilot stated "door light out" at which time he clipped all the cargo net straps on the door and on the floor. The captain reported that after takeoff at an altitude of about 600 feet, the cockpit door opened, they heard a loud noise, and the copilot confirmed that the cargo door was open. The captain reported he had the copilot call the tower to inform them that they were returning with an emergency. The captain reported the tower cleared them to land and reminded them to extend the gear. The captain reported that he repeatedly requested the copilot to lower the gear and flaps. The captain reported the gear and flaps were extended late which "...caused us to overshoot the runway centerline." The captain reported that the copilot started to call for an overshoot, but the captain replied that they were going to land. He reported that he was having difficulty controlling the airplane and he was worried about sustaining foreign object damage to the left engine from cabin debris. The captain reported that unknown to him, the copilot retracted the flaps and gear. The copilot extended the gear once again when he realized that the captain was going to land. The captain reported the nose gear extended and locked, but there was no braking. He reported he selected the electro-pump to the left and "shut the engines." The captain reported he steered the airplane away from the runway edge light and between the cement posts of the cemetery fence. The airplane came to rest 30 feet past the fence. The pilot reported that on base leg he requested that the copilot extend the flaps. When he went to move them himself, he saw the copilot move the flap handle "apparently the wrong way." The captain reported, "Had the flaps been extended when requested, there is no doubt in my mind that I would have touched on the numbers." The captain reported, "I would normally have detected the F/O odd actions immediately, but the cargo door was open [which] made the airplane behave somewhat differently than usual" and "The cockpit was very noisy, but not enough that he would not hear my commands, [which] I repeated and he acknowledged, but choose to disregard." The copilot reported, "Pre-flight planning, engine start up and taxi was conducted in accordance with standard operating procedures, in which main cargo door light was checked twice as per the check list." The copilot reported the cargo door opened shortly after takeoff. He reported that just prior to the turn from downwind to base the captain called for flaps and gear at which time he lowered the gear and extended 25 degrees of flaps. The copilot reported the captain then called for the flaps to be lowered to 40 degrees at which time he extended the flaps further. The copilot reported he then became alarmed when seeing the position of the airplane relative to the runway at which time he shouted to the captain "go miss, go miss go around." He reported the captain glanced at him momentarily and continued toward the runway. The copilot then selected gear up and raised the flaps to 25 degrees while still indicating to the captain to go around. The copilot reported the captain continued to descend toward the runway while the airplane was "dangerously low on altitude [less than] 100' AGL." The copilot indicated in a drawing that the airplane then passed through the runway centerline and the captain "...aggressively reversed bank to the right. Approximate height 50' AGL with steep angle of bank." The copilot reported that at this point he stopped his efforts for a missed approach and he lowered the gear. According to a drawing the copilot indicated that the airplane touched down about half way down the runway. A witness stated that he looked out the window and noticed the exterior door latch was not down. He reported that a truck driver also mentioned to him that the latch was up. The witness reported that the airplane was taxiing down the runway and he was unable to see if the crew had secured the latch prior to takeoff.