On May 3, 1996, at 0925 central daylight time, a Schweizer SGS-233A, N7773S, registered to and operated by a private owner as a Title 14 CFR Part 91 flight, was not damaged during a hard landing near Odessa, Texas. Visual meteorological conditions prevailed and a flight plan was not filed for the local flight. The FAA inspector (airline transport pilot/commercial glider pilot) receiving an FAA flight check, sustained serious injuries. The FAA inspector airline transport pilot/commercial glider pilot, administering the flight check, received minor injuries. During interviews, conducted by the investigator-in-charge and an FAA inspector, the pilots and the owner/operator reported the following information. The owner holds an FAA contract for the training of FAA inspectors for their commercial pilot glider rating and flight instructor glider rating. On May 2, 1996, the FAA inspector being flight checked completed both glider ratings. However, the commercial pilot glider rating contained an "aero tow only" limitation. On the morning of May 3, 1996, this FAA inspector completed an additional (FAA Form 4040) required FAA inspector glider check in order to conduct his work as an FAA glider inspector. The fourth and final flight check was then administered to remove the "aero tow only" limitation by completing several ground tow launches. The pilots and the owner further reported that following five successful ground tow launches, conducted on runway 15 of the dirt airstrip (2,652 feet long and 150 wide) with a Ford Ranchero vehicle, a discussion was held to review emergency procedures. With the winds from the south/southwest degrees at 10 to 18 knots, the 6th ground tow was initiated. When the glider airspeed had accelerated to 45 knots, the pitch attitude had attained 45 degrees, at an altitude of about 140 to 160 feet above the ground, the FAA inspector administering the flight check released the tow line. The pilot receiving the flight check pushed the glider nose full forward; however, the airspeed did not increase to the 50 knots needed for the flare. The glider landed hard, bounced, and subsequently touched down on the runway. The glider then rolled 150 feet before coming to rest off the right edge of the runway. Both pilots reported that the glider encountered "a pocket of sinking air."