On July 24, 1999, about 1140 Eastern Daylight Time, a Cessna 150, N714HS, was substantially damaged during a forced landing to a field near the Central Jersey Regional Airport (47N), Manville, New Jersey. The certificated flight instructor (CFI) and passenger received minor injuries. Visual meteorological conditions prevailed and no flight plan was filed for the instructional flight conducted under 14 CFR Part 91. The CFI stated that the flight was intended to introduce the passenger (prospective student) to flight training. They departed 47N at 1105, and after remaining in the local area for approximately 15 minutes, they returned to the airport to perform touch and go landings on Runway 25. The CFI entered the traffic pattern downwind, pulled the carburetor heat and extended flaps in preparation for landing. Upon touchdown, he added full power, retracted the flaps, pushed the carburetor heat in and rotated at a point about 2/3 down the length of the 3,509-foot runway. The airplane climbed straight ahead, and at an altitude of 400 feet above the ground and an airspeed of 62 knots, the pilot noticed that the airspeed "began to decay;" however, the engine was producing 2400-2500 RPMs. The CFI lowered the nose of the airplane in an attempt to gain airspeed, and at 200 feet above the ground, the airspeed had decayed further. He did not change the configuration of the airplane and performed a forced landing to a field northeast of his current position. The airplane touched down and impacted a rise in the terrain, which sheared off the nose gear. The airplane came to rest in a nose down attitude. The passenger reported that he and the pilot returned to 47N, to perform touch-and-go landings, after flying in the local area for 30 minutes. During the climbout after the first touch-and-go, the CFI leveled the airplane off at 500-600 feet and did not say anything. The passenger then noticed that they were "gradually getting lower and lower," when the CFI banked the airplane and they landed in a field. After exiting the airplane, the CFI explained that they had "not produced enough power to gain altitude," because they may have been "too big" and it was "too hot" of a day for the airplane to perform. The passenger additionally stated that the engine produced power and the propeller continued to turn throughout the entire flight. He did recall that the CFI mentioned the carburetor heat, after he noticed that there was a problem. A Federal Aviation Administration Inspector reported that the firewall of the airplane was destroyed, the wings and wingtips of the airplane were wrinkled, and the wing spars were crumpled. He stated that the carburetor heat was found in the "on" position, the throttle was retarded, and the mixture was found "in". In addition, the fuel selector was found in the "off" position. The owner of the airplane stated to the Inspector that he had drained fuel from the airplane into a drum before the Inspector arrived. The owner and Inspector then determined that approximately 11.6 gallons of fuel was contained in the drum. The engine of the airplane was examined at a storage facility by a Safety Board investigator. The engine, which had remained attached to the firewall of the airplane, was bent 90 degrees downward from the firewall. The engine was rotated by hand using the propeller flange, which remained attached to the engine. Thumb compression and valve train continuity was confirmed to all cylinders. All spark plugs except for the #3 and #4 bottom plugs were removed, their electrodes were intact and light gray in color. The left magneto was intact. The right magneto was damaged at the base, but operated normally. Spark was visually observed on all leads. The carburetor exhibited damage to the attachment flange, and the venturi butterfly moved freely. The carburetor heat was observed extended in the mid range position, which was consistent to the lever located at the carburetor heat box. According to the Cessna airplane manual, the checklist procedure for takeoff included assuring that the carburetor heat was in the cold position. In addition, the basic empty weight of the airplane was 1,109 pounds, and the maximum takeoff weight was 1,600 pounds. The passenger reported his weight as 250 pounds, and estimated the pilot's weight as 200 pounds. The CFI determined there was 14 gallons of fuel onboard the airplane before takeoff. The airplane was last fueled on July 18, 1999, with 5.8 gallons of fuel, and flew about 2 hours since that date. According to the temperature and elevation reported at 47N, the density altitude was calculated as 1,747 feet.