On October 3, 1999, at 1312 hours Pacific daylight time, an experimental Giles G-750 airplane, N17HE, collided with terrain during an airshow performance at the Salinas, California, airport. The airplane was owned and operated by Wayne Handley Aerosports, Inc., of Greenfield, California, and incurred substantial damaged. The commercial pilot received serious injuries. Visual meteorological conditions prevailed for the air show exhibition flight operating under 14 CFR Part 91 and no flight plan was filed. The pilot was to perform a 1-minute aerial sequence, which started and stopped at the same spot on the runway. According to ground witnesses, the pilot was nearing completion of a modified Cuban-8 type maneuver when the airplane descended and collided with the terrain on taxiway "C." The propeller had the capability of Beta range operation and was reversible to produce zero or negative thrust. In his written statement, the pilot said that near the completion of the performance he established a descent angle about 50 to 60 degrees. After operating slightly in Beta reverse range, the pilot brought the propeller out of Beta to flight idle as the airplane passed through 800 feet agl. He moved the thrust lever forward to achieve 85 to 90 knots and realized that the engine was not spooling up. He stated that he believed the engine might have flamed out. He maintained a nose down attitude with the airspeed on the verge of a stall. During the descent to ground impact, the pilot briefly maintained the minimum sink rate, but it increased just prior to ground contact. The PT6A-25C engine was shipped to Pratt and Whitney Canada for examination and disassembly. According to their report, the engine displayed contact signatures to its internal components characteristic of the engine developing power at impact, likely in the middle to high power range. There were no indications of any anomalies or distress that would have precluded normal operation prior to impact. As part of the examination, functional checks of the fuel pump and fuel control unit were conducted; the components functioned within specification. A copy of the report is attached. The Hartzell HC-B3MN-3/M10083 propeller was disassembled and examined at the Hartzell factory. According to the report of the examination, internal witness marks and other evidence establish that the propeller blades were at operating angles between 20 and 27 degrees at ground impact. Hartzell reported that the flight idle blade angle is 9 degrees and reverse is -18 degrees. A copy of the report is attached.