Accident Details
On May 2, 2012, at approximately 1700 Hawaii standard time, a Robinson R22 Beta helicopter, registration N209KR, was substantially damaged during a hard landing following a reported partial loss of engine power near Kailua-Kona, Hawaii. The helicopter was operated by Mauna Loa Helicopters of Kailua-Kona. The certified flight instructor (CFI) and student pilot on board were not injured. Visual meteorological conditions prevailed at the time of the accident. The instructional flight was conducted under 14 Code of Federal Regulations Part 91, and no flight plan was filed. The flight had departed Kona International Airport (HKO) at about 1630.
Pilot Reports
According to the CFI, after departure the student climbed upslope to about 2,000 feet mean sea level (msl) to practice off-airport landings. The student began orbiting a suitable landing area at about 1,500 feet msl with a slow descent. As it started to sprinkle, the CFI instructed the student to turn the carburetor heat on. At approximately 300 feet above ground level (agl), the CFI heard mechanical sounds similar to a poorly running engine, followed by a loss of lift and rotor rpm. The CFI took control, lowered the collective, and rolled on the throttle. When rotor rpm did not recover, he initiated a full autorotation and applied aft cyclic to prevent stalling the main rotor. Rolling the throttle on and off produced no change in engine rpm, leading the CFI to assume the engine had quit. During the autorotation, he instructed the student to attempt an engine restart. The CFI made an 80-degree turn upslope to clear trees. Before landing, he heard the starter turning over. During the flare, insufficient airspeed prevented a successful landing, resulting in a hard landing upslope. After landing, the engine was found running at idle; the CFI believed the student had started it on the third attempt.
The student pilot reported that at about 200 to 300 feet agl, with carburetor heat full on, the engine began losing power, first indicated by an unusual noise. The instructor took control and directed the student to start the engine. The student attempted three unsuccessful restarts while the CFI manipulated the throttle. The low rotor rpm horn activated. At about 20 to 30 feet agl, with the collective fully raised, aircraft control was lost. After landing, the low rotor horn remained on, the main rotor blades were still turning, and the student heard the engine running.
Postaccident Examination
A postaccident examination of the helicopter was overseen by representatives from the National Transportation Safety Board (NTSB) and the Federal Aviation Administration (FAA). The engine inspection, conducted while the engine remained attached to the helicopter at the operator's maintenance facility at HKO, found the spark plugs in good condition except for the #4 cylinder bottom plug showing small lead deposits and the #4 top plug showing a small amount of carbon deposit. All spark plugs emitted spark, ignition leads fired, and both magnetos were functional. The valve train was intact with no push rod deformation, and intake and exhaust valves opened and closed properly. Compression was confirmed for each cylinder. The carburetor's venturi showed no contamination, and the air induction filter had impact damage but no contamination. The carburetor heat control cable was intact. A fuel sample from the gascolator showed no contamination. The engine was started and run for about one minute at idle power, with no anomalies noted. The reason for the reported partial loss of engine power was undetermined.
Weather Conditions
At 1653, the weather reporting facility at Kona International Airport reported wind from 180 degrees at 10 knots, visibility 10 miles, overcast clouds at 6,000 feet, temperature 27 degrees Celsius, dew point 16 degrees Celsius, and an altimeter setting of 29.95 inches of mercury. A carburetor icing probability chart indicated that, given the ambient temperature and dew point, serious carburetor icing at glide power was favored.