On April 8, 1994, at 1317 mountain daylight time, a Piper PA-32RT-300T, N881GK, was destroyed during a forced landing near Centennial Airport, Englewood, Colorado. The certified flight instructor (CFI) and commercial pilot receiving instruction sustained serious injuries. Visual meteorological conditions prevailed for the instructional flight. The following is based on the pilot/operator report. The airplane had 90 gallons of fuel onboard prior to its 1210 departure. After performing various maneuvers in the practice area, the pilots returned to the airport for takeoffs and landings. The second pilot said that the engine was not producing sufficient power while on the crosswind leg. The CFI noted the throttle was fully open but the engine was producing only 2400 RPM and 30 inches of manifold pressure. He assumed control of the airplane while the pilot receiving instruction made sure the fuel pump was on, switched to the left tank, and advised the tower of their predicament. The CFI attempted to land west of the runway but the airplane struck a fence and impacted terrain in a field about 1,000 feet north of the departure end of runway 35L. The engine and accessories were later functionally checked and tested. No discrepancies were found.