On April 16, 1998, at 1545 mountain daylight time, an Enstrom 280C helicopter, N5693D, sustained substantial damage during an emergency landing while on an instructional flight near Castle Rock, Colorado. The certified flight instructor and student were not injured. Visual meteorological conditions prevailed, and no flight plan was filed for this local area flight which originated at Centennial Airport, Englewood, Colorado, at 1530. The flight was operating under Title 14 CFR Part 91 when the accident occurred. According to the flight instructor, he was conducting an introductory flight with a new student. Fifteen minutes after departure, he began demonstrating emergency procedures. While approximately 400 feet above the ground, he reduced the throttle to 2000 rpm. After scanning the instrument panel, he noted the rotor rpm was indicating 350, and the engine rpm was indicating 0. He "lowered the collective to [the] stop, rolled the throttle back and forth, and depressed the starter for approximately 300 feet - 9 seconds." Determining that the ground was unsuitable for landing, he turned south and aimed for a "flat place in [a] gully." He cushioned the landing with the collective, then sank 6 inches into the ground. The helicopter stopped abruptly, then rolled forward. The main rotor struck a berm, causing "rotor torque to be transferred to [the] fuselage, twisting it to [the] left." In a nose down attitude of approximately 20 degrees, the fuselage turned 180 degrees with a nose high attitude of about 70 degrees. Examination of the engine disclosed no abnormalities; however, a postaccident functional test of the engine revealed a malfunction in the engine-driven fuel pump. After a normal start, the engine ran for approximately two minutes and the throttle was advanced to 2,900 rpm. After five minutes of operation, the engine sounded steady and normal indications were present. When the electrically-driven boost pump was switched to the OFF position, power fluctuations were noted with the engine-driven fuel pump operating. The engine was shut off for approximately five minutes, then restarted. The engine was operated with both the electric fuel pump ON and OFF. During periods with the electrically-driven boost pump OFF, the engine rpm indications on the tachometer fluctuated approximately 700 rpm. All three rotor blades were bent, and the tail boom was severed.