On July 19, 2002, at 1445 central daylight time, a Piper PA28-140, N8220N, piloted by a private pilot, was substantially damaged when it impacted a tree line approximately 120 yards from the end of the runway on takeoff. The airplane was departing runway 18 (2,430 feet x 25 feet, turf) from the El Dorado Springs Memorial Airport (87K), El Dorado Springs, Missouri. The flight had originated from the Bolivar Municipal Airport (M17), Bolivar, Missouri, approximately 20 minutes prior to the accident, with the intention of practicing takeoffs and landings on the turf runway at 87K. Visual meteorological conditions prevailed at the time of the accident. The flight was being conducted under 14 CFR Part 91 and was not on a flight plan. The pilot sustained minor injuries and the certified flight instructor (CFI) on-board sustained serious injuries in the accident. In a written statement, the pilot noted "(my flight instructor) had scheduled me in between 1:30 pm and 3:30 pm to do some actual soft field work as I had never taken off or landed on turf." They had landed on runway 18 at El Dorado Springs and back-taxied to the intersection with runway 4-22. Approximately 1,830 feet was available from the intersection. The aircraft was configured with 2 notches (25 deg) of flaps in accordance with the Pilot's Operating Handbook (POH). Full power was applied prior to brake release, with full "up" elevator. At approximately the halfway point, the pilot thought that the aircraft was not accelerating as required and began to initiate an abort. The flight instructor stated "We should be fine." At which point the pilot returned to full power and continued the roll. "I continued to check the airspeed indicator and it was coming up but slowly. I believe when we reached the point of no return is when [the flight instructor on-board] grabbed the control yoke and pull[ed] full back. I do remember seeing the end of the runway go under us, but don't remember the aircraft sinking as we went off." The airplane impacted the tree line appoximately 120 yards from the end of the runway. Additionally, the pilot noted that "We did not know what the OAT [outside air temperature] was, we did not do a density altitude calculation." The flight instructor, in his written statement, noted "[The pilot] had asked me if I would like to go with him to land and takeoff on a turf runway at El Dorado Springs. The takeoff roll seemed normal and at rotation I believe we had a partial power loss or anyway a reduction of power of some kind. I believe that we contacted the ground and, at that point, I knew we were not going to clear the trees." Weather conditions at the scene were reported by the pilot as 3,000 feet scattered, 10 miles visibility, southwest winds and light turbulence. He did not report wind speed or altimeter setting. The Federal Aviation Administration (FAA) inspector on-scene reported a field temperature of 98.7F (37C). Weather conditions at the Springfield-Branson Regional Airport (SGF), located 47nm to the southeast, at 1454 cdt, were reported as wind variable at 4 knots, 10 miles visibility and few clouds at 4,000 feet. Temperature and altimeter setting were reported at 32C and 30.00in Hg, respectively. Applying these conditions at El Dorado Springs resulted in a calculated density altitude of 3,085 feet. Consulting the Pilot's Operating Handbook, the takeoff distances required at 3,000 feet standard altitude and 1,950 lbs. gross weight are 900 feet ground run and 1,950 feet over a 50 ft. obstacle. The chart does not specify a runway surface or condition. Later model PA28-140 operating handbooks denote takeoff data as being applicable to a paved, level, dry runway. No further guidance is offered regarding other runway surfaces or conditions. The Pilot's Handbook of Aeronautical Knowledge, AC61-23C, Chapter IV -- Airplane Performance, notes that "Air density is perhaps the single most important factor affecting airplane performance. It has a direct bearing on the power output of the engine, efficiency of the propeller, and the lift generated by the wings... . An increase in air temperature or humidity, or decrease in air pressure resulting in a higher density altitude, significantly decreases power output and propeller efficiency." Concerning runway surface condition, the handbook states "The takeoff distance is affected by the surface condition of the runway. If the runway is muddy, wet, soft, rough, or covered with tall grass, these conditions will act as a retarding force and increase the takeoff distance." FAA accident prevention publication Flight Sense, FAA-P-8740-1, suggests that runway lengths be increased at least 10% for short grass. In addition, it recommends adding a safety factor of at least 25% over and above increments applied for density altitude and runway conditions. The pilot held a private pilot certificate with airplane single engine land and instrument airplane ratings. He accumulated 238 hours total time, with 157 hours in the same make and model as the accident aircraft, and 40 hours flown within the past 90 days. He completed a flight review on June 6, 2002. The flight instructor on-board held a commercial pilot certificate with airplane single-engine and multi-engine land and instrument airplane ratings. His flight instructor certificate had airplane single engine and instrument airplane ratings, and is valid through August 2002. He reported approximately 2,700 hours total time, with 100 hours flown within the preceeding 90 days. The 1969 Piper Cherokee 140 (PA28-140) involved in the accident, S/N 28-25424, had accumulated 7,832 hours total time and 105 hours since last inspection. This was an annual inspection which was completed on August 14, 2001. The Lycoming O-320 engine installed, S/N L19466-27A, had accumulated 964 hours since overhaul and 105 hours since last inspection. The pilot did not report any malfunctions associated with the engine or airframe prior to, or at the time of, the accident.