On July 19, 2017, about 1010 Pacific daylight time, an Enstrom F28-C rotorcraft, N5697B, descended rapidly and landed hard in a dirt pasture about 1/2-mile northeast of the Chino Airport (CNO), Ontario, California. The student pilot, sole occupant, was seriously injured and the helicopter sustained substantial damage to the tailboom and main rotor blades. The helicopter was registered to Dubois Aviation Inc and operated by the pilot as a 14 Code of Federal Regulations Part 91 solo instructional flight. Visual meteorological conditions prevailed and no flight plan was filed. The flight originated from CNO about 1005. The student pilot reported he entered the downwind leg to set up for the first landing of the day. When abeam his touchdown location, he conducted the prelanding checks with no anomalies noted. Prior to turning base he lowered the collective, reduced the throttle, and started to descend at about 100 feet per minute. During the descent, he observed the engine RPM to be slightly above 2,900 RPM, and he reduced the throttle. The RPMs reduced slightly, however, went back to 2,900 RPM, and the manifold pressure was about 10 inches of Hg. About 400 feet above the ground, he heard the engine sound increase and he observed 3,300-3,500 RPM. Unable to make the runway, he continued to descend towards a pasture and landed hard in the dirt. A postaccident airframe and engine examination revealed no preimpact anomalies that would have precluded normal operation. Flight control continuity was established from the cockpit controls to the main rotorhead. The tailrotor driveshaft was turned and rotation was observed from the tail rotor gear to the main rotor mast. The main rotor blades remained intact and exhibited signatures consistent with coning. The lower spark plugs were removed from the engine and the engine was rotated from the cooling fan. Thumb compression was obtained on all cylinders in proper firing order, and the impulse coupling was heard clicking from the left magneto. The spark plugs were reinstalled, and the engine was prepared for an engine run. The engine ran normally for several minutes at various RPMs. Normal operating pressures and temperatures were observed, and there were no fuel or oil leaks observed. The engine was shutdown normally with no anomalies noted.