Aircraft and Flight Information
On August 26, 2016, at approximately 0745 Hawaii standard time, a Robinson R44 II helicopter, registration N74805, was substantially damaged following a loss of control after landing at the Kona International Airport at Keahole (HKO), in Kailua/Kona, Hawaii. The helicopter was engaged in an instructional flight under 14 Code of Federal Regulations Part 91, with visual meteorological conditions prevailing. No flight plan was filed. The local flight had departed HKO about 0715.
Accident Narrative
The certified flight instructor (CFI), who was the pilot in command, reported that after entering the North Practice Area, he directed the pilot under instruction (PUI), also a CFI, to perform an approach to a spot on a gravel road. The PUI began a left downwind approach, turned to base and final, and the CFI instructed him to complete the approach to a full stop. The initial touchdown was smooth, but as the PUI lowered the collective fully, the helicopter began rocking fore and aft. The intensity increased rapidly, and the CFI took over the controls, but the helicopter entered uncontrollable flight. It oscillated intensely and came to rest about 20 to 30 feet from the initial touchdown point, at an angle of more than 45 degrees to the forward left. The fuselage sustained substantial damage from impact with terrain.
The PUI reported that after a smooth approach and touchdown, a strong rocking motion with heavy vibrations began. Lowering the collective worsened the situation, and pulling up caused the helicopter to move forward and left approximately 10 feet. Cyclic inputs were ineffective, and the helicopter crashed nose-first with a main rotor blade strike. No dynamic rollover occurred. After the helicopter stopped, the mixture was pulled to shut down the engine.
Post-Accident Examination
On October 4, 2016, Federal Aviation Administration aviation safety inspectors examined the helicopter. The tailcone cowling attach points showed no damage or defects. Torque checks on the tailcone attaching hardware revealed that the nuts moved at 355 inch-pounds, below the manual specification of 655 inch-pounds; however, no elongation or damage to bolts, washers, skin, or structure was noted. The tailcone was removed for inspection.
Flight control servos, push-pull tubes, and the main rotor torque tube were examined with the mast fairing removed. No damage or defects were found. Full range of motion was verified with and without hydraulic power, and control continuity and operation appeared normal.
The main rotor gearbox mounts were inspected after removing the tailcone and fuel tanks. The rubber portions and mounting ears showed no damage or defects. Torque on the main transmission bolts measured 90 foot-pounds, consistent with the maintenance manual.
Injuries and Damage
The CFI and PUI were not injured. The helicopter sustained substantial damage to the fuselage due to impact with terrain.