On August 26, 2016, about 0745 Hawaii standard time, a Robinson R44 II helicopter, N74805, was substantially damaged following a loss of control after landing at the Kona International Airport at Keahole (HKO), Kailua/Kona, Hawaii. The certified flight instructor (CFI) and pilot under instruction (PUI), who is also a CFI, were not injured. Visual meteorological conditions prevailed during the instructional flight, which was being conducted in accordance with 14 Code of Federal Regulations Part 91, and a flight plan was not filed. The local flight departed HKO about 0715. In a written report submitted to the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), the CFI/pilot in command, reported that as they entered the North Practice Area (NPA) he instructed the PUI to make the first approach to a spot in the middle of the gravel road, which would provide plenty of clearance. The CFI stated that the spot chosen was one of the gravel roads in the NPA, which has a wide area, and is flat and smooth with no large rocks. The CFI further stated that the PUI began his approach on a left downwind, then turned on to base and final "…and everything was looking great. I told him to complete the approach to a full stop on the ground." The CFI reported that the approach was smooth, and that the initial set down was very soft and smooth as well. The CFI opined that once the skids were on the ground, the PUI continued to lower the collective towards the full down position, at which time the helicopter began to rock in a fore and aft motion. The CFI stated that as the intensity quickly increased he came on the controls, and from that point on all that he could recall was that "…we were in the air again in uncontrollable flight." The CFI reported that the helicopter was oscillating intensely, then came to a stop about 20 to 30 ft and a little more than a 45° angle to the forward and left of the initial touchdown point. The helicopter sustained substantial damage to the fuselage as a result of impact with terrain. In a statement submitted to the NTSB IIC, the PUI reported that he and his instructor departed from Kona Airport around 7:50 am local time, for the North practice area. Everything was good, and he performed a controlled and smooth normal approach to a flat well open area. The skids touched the ground and then a strong rocking aft and forward movement accompanied by heavy vibrations started. He tried to lower the collective but made it worse, so he tried to pick up to correct, then it felt like the helicopter shot out forward/leftwards approximately 10 feet away from landing spot. He recalled that the cyclic did not respond to inputs well enough, and ended up crashing nose first with a main rotor blade strike in the ground, no dynamic rollover happened. As soon as the helicopter stopped moving, the mixture was pulled out to shut down the engine. On October 4, 2016, Federal Aviation Administration aviation safety inspectors assigned to the Honolulu Flight Standards District Office, Honolulu, Hawaii, examined the helicopter. The tailcone cowling attach points were inspected with the tailcone installed. No damage or defects were noted. The torgue on the tailcone attaching hardware using a calibrated torque wrench was checked. The torque was 655-inch pounds per the manual. The torque broke (nut moved) at 355-inch pounds on all bolts. Additionally, the tailcone was removed and no elongation or damage to the bolts, washers, skin or structure were noted. Flight Control Servos and Push-Pull Tubes With the mast fairing removed, the main rotor torque tube, control tubes and servos were examined. No damage or defects were noted. The flight controls were moved through a full range of motion with and without hydraulic power. Control continuity and operation appeared to be normal. Main Rotor Gearbox Mounts The main rotor gearbox mounts were inspected with the tailcone and both fuel tanks removed. The inspection of the mounts' rubber portion, as well as the associated ears of the mounts, revealed no damage or defects. Using a calibrated torque wrench, the torque registered on the main transmission bolts was 90-foot pounds, which was consistent with the value denoted in the maintenance manual.