On September 20, 2005, at 1528 eastern daylight time, a Piper PA-28-180, N6494J, was substantially damaged when it impacted trees during a go-around at the Millville Municipal Airport (MIV), Millville, New Jersey. The certificated flight instructor and the certificated private pilot received serious injuries. Visual meteorological conditions prevailed, and an instrument flight rules (IFR) flight plan was filed for the flight. The instructional flight was destined for the Atlantic City International Airport (ACY), Atlantic City, New Jersey, and was conducted under 14 CFR Part 91. According to the flight instructor, after takeoff from runway 28 at MIV, and while at an altitude of 600 feet msl, the pilot initiated a right turn toward the Cedar Lake VOR. During the turn, the engine began to "run rough," and the engine rpm decreased to between 1,800 - 2,000 rpm. He instructed the pilot to return to MIV, at approximately 500 feet, and the pilot reduced power, applied flaps, and set up the airplane for a downwind landing on runway 10. During the landing, the airplane had not touched down, as it continued halfway down the runway. Because there was a jet aircraft waiting at the departure end of the runway, and workers with equipment at the runway intersections, the pilots elected to perform a go-around. They applied full power, and initiated a "slight" climbing right turn above trees at the departure end of runway 28, and then a left turn to return for landing on runway 28. During the turn, the airplane "entered an accelerated stall," and the left main landing gear impacted the ground. The airplane continued across a grass area and struck a group of trees. A Federal Aviation Administration (FAA) inspector examined the engine after the accident. According to the inspector, the number 3 cylinder contained a crack from the spark plug hole, to a point between the cylinder intake and exhaust valve. Examination of maintenance records for the airplane revealed the number 2 and number 3 cylinders were replaced with reconditioned cylinders on January 17, 2000. Since that date, the engine accumulated 1,287 hours of flight time. The most recent annual inspection was performed on July 12, 2005. The compression check values for the number 2 and number 3 cylinders were 72/80 psi and 74/80 psi, respectively. The average compression check values for all four cylinders over the previous 5 years was between 68/80 psi and 76/80 psi. The winds reported at MIV, at 1454, were from 250 degrees at 7 knots. The airport consisted of two runways; runway 10/28, which was 6,002 feet long by 150 feet wide, and runway 14/32 which was 5,057 feet long by 150 feet wide.