History of Flight
On March 13, 2008, at 0940 eastern daylight time, a Robinson R22 Beta II, registration N2215R, was substantially damaged during a forced landing in Wilmington, North Carolina. The certificated commercial pilot, who was the sole occupant, was fatally injured. The flight departed Wilmington International Airport (ILM) under day visual meteorological conditions with no flight plan filed. The personal flight was conducted in accordance with Title 14 Code of Federal Regulations Part 91. According to airport personnel, the pilot intended to fly south to take aerial photographs of a business, then proceed to pick up a student for a training lesson.
A witness located about half a mile from the accident scene observed the helicopter pass overhead and noted that the engine was spitting and sputtering. The helicopter appeared to be about 50 feet above pine trees estimated at 150 feet. Another witness reported that the helicopter was just above the top of a billboard sign when first noticed, and saw parts shedding to the south before it reversed direction. The witness then lost sight of the helicopter behind a building and observed smoke. A third witness saw parts falling, the helicopter impacting the ground, and subsequent fire. There was no radar track of the helicopter, and no onboard recording devices were located.
Personnel Information
The pilot held a commercial pilot certificate with ratings for airplane single-engine land, airplane multiengine land, rotorcraft-helicopter, and instrument airplane and helicopter. He did not hold a flight instructor certificate. The pilot's most recent second-class medical certificate was issued on February 7, 2008. According to his logbook, he had accumulated 542 total helicopter flight hours, with 433 hours in the accident helicopter make and model. He completed the Robinson Helicopter Company Pilot Safety Course on November 16, 2006, with a rating of "average."
Aircraft Information
The helicopter, serial number 3084, was registered to Maintenance Services LLC, Rocky Point, North Carolina. It was a two-seat, single main rotor, single-engine helicopter manufactured in February 2000. It was powered by a Lycoming O-360-J2A engine. The maximum gross weight was 1,370 pounds. The tail rotor drive shaft was enclosed in a tapered tail boom and included a damper bearing assembly designed to dampen shaft oscillations.
The most recent annual inspection was completed on December 14, 2007, at 1,389 hours of operation. The engine's most recent 100-hour inspection was completed on October 13, 2007. The last maintenance, an engine oil and oil filter replacement by the accident pilot, occurred on March 6, 2008, at 1,461 total hours.
Meteorological Information
At 0953, the recorded weather at ILM, about 8 miles north of the accident site, included winds from 230 degrees at 4 knots, visibility 10 miles, clear skies, temperature 17 degrees Celsius, dew point 4 degrees Celsius, and an altimeter setting of 30.03 inches of mercury.
Wreckage and Impact Information
The helicopter impacted in an open lot approximately 3 feet from several storage trailers. The wreckage exhibited impact and post-impact fire damage. The debris path was on a heading of 342 degrees, and the helicopter came to rest at a heading of about 140 degrees. The tail cone separated from the fuselage at a right angle, with no leading edge damage on the tail rotor blades. Pieces of the main rotor blade, empennage, and anti-collision beacon were collocated about 350 feet south of the main wreckage.
Examination revealed spanwise coning of the main rotor blades, with sections of trailing edge missing from both blades. One blade section bore an impression consistent with the leading edge of the vertical stabilizer. The main rotor system rotated without binding. The tail rotor drive shaft forward flex plate exhibited rotational distortion and separation from yokes, while the aft flex plate was undamaged. The damper bearing assembly was damaged; its inner race remained in place, but the outer race and bearings were missing. It could not be determined if the assembly operated as intended before the accident. The interior of the tail cone showed rotational scoring, and electrical wires and push-pull tubes were displaced.
The engine crankshaft rotated with continuity confirmed. Cylinder 2 produced minimal compression due to compressed intake valve springs, but no other anomalies were found. The carburetor bowl, fuel nozzle, and fuel lines were damaged. The mixture control was in the full rich position, and the throttle plate was about three-quarters open. Spark plugs were dark gray with intact electrodes. The carburetor fuel inlet screen was free of debris. Oil was visible throughout the engine, and the oil filter element was charred with no metallic debris. Magnetos were thermally damaged and untestable.
The instrument panel was fire-damaged; the engine rpm needle was near the upper limit and the rotor rpm needle near the lower limit, but it could not be determined if these were the indications at the time of the accident. The ignition key position was undetermined.
Additional Information
A postmortem examination determined the pilot's cause of death as massive blunt trauma. Toxicological testing revealed no anomalies.
The NTSB Materials Laboratory examined the intermediate flex plate, a portion of the push-pull tube, a portion of the main tail rotor drive shaft, and the bearing assembly housing. All fractures were consistent with overstress separation due to the accident; no mechanical malfunctions were found.
The Robinson Helicopter Company Safety Notice SN-34 addresses aerial survey flights, recommending pilots have at least 500 hours pilot-in-command and extensive training in low rpm and settling-with-power recovery. Safety Notice SN-36 warns that overspeeds can cause tail rotor drive shaft vibration leading to failure, noting the damper is ineffective above 120% RPM.
Testing documentation indicated that whirl modes on the R22 occur at specific rotor rpm: 15.2%, 60.6%, and 132.0%. The first two are below the normal operating range, while the third could occur during an overspeed. The manufacturer's maximum operating main rotor rpm limit is 102%.
An FAA publication on winter flying discusses carburetor icing conditions. Interpolation of a carburetor icing probability chart showed that atmospheric conditions were conducive to serious icing at glide power. The helicopter was equipped with a carburetor heat assist device, but the carburetor heat knob could be locked in the off position. The Carburetor Air Temperature (CAT) gauge had been reported inoperative before the flight.
The FAA-approved flight manual includes emergency procedures for power failure, requiring immediate collective lowering to maintain rotor rpm, entering autorotation, and establishing a glide at 65 knots, with collective adjustments to keep rotor rpm in the green arc.
No probable cause was stated in the source.