On May 3, 2001, at 1300 central daylight time, a Cessna 172RG airplane, N9696B, was substantially damaged during a forced landing following an in-flight fire near Washington, Oklahoma. The airplane was registered to Christensen Aviation Inc., of Wilmington, Delaware, and operated by Airman Flight School, Inc., of Norman, Oklahoma. The flight instructor and private pilot receiving instruction sustained minor injuries. Visual meteorological conditions prevailed and a flight plan was not filed for the 14 Code of Federal Regulations Part 91 instructional flight. The local flight originated from the University of Oklahoma Westheimer Airport, Norman, Oklahoma, at 1230. According to the flight instructor and pilot receiving instruction, the student was demonstrating a commercial flight maneuver at 2,100 feet agl, when they smelled an odor similar to "electrical burning." The instructor told the student to terminate the maneuver and return to the Westheimer Airport. While the student was terminating the maneuver, visible smoke appeared in the cabin and heat was felt coming from beneath the instrument panel. The instructor assumed control of the airplane. The engine was shut down, and a forced landing was executed to a field. During the landing, the airplane encountered soft terrain, nosed over and came to rest inverted. According to an FAA inspector, who examined the airplane, a plastic hydraulic reservoir from the hydraulic power pack was found melted and laying on the cockpit floor. He stated that the left wing-tip, the right wing strut, and the vertical stabilizer were structurally damaged. He added that the engine firewall was buckled. The hydraulic power pack was examined and functionally tested at Aero Electric Inc., Wichita, Kansas, under supervision of the FAA. According a report from Aero Electric, the power pack and its related components operated within manufacturer's specifications.