On September 2, 2013, about 1540 eastern daylight time, a Mooney M20C, N78951, operated by a private individual, was substantially damaged when it collided with trees during takeoff from Freeway Airport (W00), Mitchellville, Maryland. The private pilot and two passengers were seriously injured. The personal flight was conducted under the provisions of 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed and a visual flight rules flight plan was filed for the planned local flight.The airplane was owned by the pilot and based at W00. It was departing on runway 36, a 2,420-foot-long asphalt runway. Due to his injuries, the pilot did not recall the accident. He estimated that the airplane was approximately 38 pounds below its maximum gross weight at takeoff. Two witnesses, in their respective vehicles, were traveling on a highway perpendicular to the departure end of runway 36. Both witnesses reported that the airplane crossed the highway at a low altitude. One of the witnesses added that the airplane's "…nose appeared higher than its tail…" as it crossed the highway and descended to a height of about 10 feet above the ground before impacting trees. A video recorder, which was installed on a parked airplane at W00, captured part of the accident airplane's takeoff. Review of the video revealed that the accident airplane initially climbed out of ground effect; however, in then began to settle back down toward the ground in a nose-up attitude prior to exiting the frame. Examination of the wreckage by a Federal Aviation Administration inspector revealed that the airplane came to rest upright, in a grassy area off the side of the highway, about 250 feet beyond the departure end of the runway. Fuel was present in both fuel tanks and the fuel selector was positioned to the left fuel tank. The inspector observed that the landing gear and flaps were both in the extended position. In addition, the flap position indicator was in the "DN" (full extended) position. He also noted that one propeller blade exhibited s-bending, chordwise scratching, and leading edge gouging. Except for the flaps position, the inspector did not observe any other anomalies with the airframe or engine. The four-seat, low-wing, retractable tricycle-gear airplane, serial number 2140, was manufactured in 1962. It was powered by a Lycoming O-360, 180-horsepower engine, equipped with a Hartzell constant-speed propeller. The airplane's most recent annual inspection was completed on December 31, 2012. At that time, the airplane had accumulated 3,702.83 total hours of operation. The engine had also accumulated 3,702.83 total hours and 1,163.49 hours since major overhaul. The pilot reported a total flight experience of 388 hours; of which, 168 hours were in the accident airplane. The pilot had flown 5 hours and 3 hours during the 90-day and 30-day periods preceding the accident, respectively. Those hours were all flown in the accident airplane. The recorded weather at 1540, at an airport located approximately 5 miles northwest of the accident site, included calm wind, visibility 10 miles, scattered clouds at 5,000 feet, and temperature 32 degrees C (90 degrees F). Review of a checklist recovered from airplane revealed, "…RUNUP & TAKEOFF…Flaps – two pumps…" Review of a make and model owner's manual revealed: "Flaps The wide span flaps are hydraulically controlled by a hand operated pump which actuates a hydraulic cylinder. A relief valve is provided which releases the flaps at a slow rate as the springs (or air pressure) raise them. Hydraulic fluid used is the same as the brake system fluid and is stored in the brake reservoir on the aft side of the firewall. To lower the laps, first set the flap-shaped control (adjacent to the flap handle) in the down position. Then pump the handle to obtain the desired setting: two strokes for take-off; four and one-half strokes for full deflection or any intermediate setting. To raise the flaps, place the control in the up position. The flaps will then rise at a controlled rate to the up position or they may be stopped at an intermediate position by placing the control in the down position again. The position of the flaps is indicated by a pointer on the aft side of the nose wheel well. The intermediate mark in the pointer range is for the flap take-off setting. " Further review of a make and model owner's manual, takeoff and climb data, revealed that at a maximum gross weight of 2,575 pounds, at 2,500 above sea level (density altitude), at 90 degrees F, the airplane required 1,345 feet of ground run or 2,305 feet to clear a 50-foot obstacle. The data assumed a takeoff configuration of the landing gear extended, mixture full rich, flaps extended 15 degrees (takeoff position), wind calm, and a hard surface runway. There was no data for a flaps full-extended takeoff.