On January 12, 1995, at 1722 central standard time, N37239, an Interstate S-1A, was destroyed by fire after the pilots made a forced landing near Amarillo, Texas. The flight instructor and the certificated pilot receiving instruction were not injured. Visual meteorological conditions prevailed. The following is based on the pilot/operator report and pilot interviews. The pilots had been flying in the west practice area for 25 minutes, doing S-turns across a road and other commercial maneuvers. The front seat pilot told the flight instructor he "smelled something funny." Smoke appeared from beneath the front floorboards, followed shortly thereafter by flames. The flight instructor made an emergency landing in an open field about four miles west of Amarillo, and both pilots evacuated the airplane. The airplane was totally consumed by fire. A Federal Aviation Administration airworthiness inspector examined the airplane and reported the fire was confined aft of the firewall, but he was unable to identify the ignition source. The airplane was not equipped with an electrical system. The engine and exhaust system were intact and no anomalies were noted.