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N2215R accident description

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Tail numberN2215R
Accident dateMarch 13, 2008
Aircraft typeROBINSON R22 Beta II
LocationWilmington, NC
Near 34.124723 N, -77.898333 W
Additional details: None

NTSB description

HISTORY OF FLIGHT

On March 13, 2008, at 0940 eastern daylight time, a Robinson R22 Beta II, N2215R, was substantially damaged during a forced landing in Wilmington, North Carolina. The certificated commercial pilot was killed. Day visual meteorological conditions prevailed, and no flight plan was filed for the local flight which departed the Wilmington International Airport (ILM), Wilmington, North Carolina. The personal flight was conducted under the provisions of 14 Code of Federal Regulations Part 91.

According to airport personnel, the non-certificated flight instructor was planning to fly south in order to take aerial photographs of a business and then proceed to another location to pick up a student for a training lesson.

A witness, located about one-half mile from the accident scene, observed the helicopter flying overhead and stated that "the engine was spitting and sputtering." Another witness stated that, the helicopter appeared to be just above the top of a billboard sign when she first noticed it. She stated that she "saw parts shedding to the south then [it] started to reverse direction." The witness then lost sight of the helicopter behind the roof of a building and observed smoke. According to another witness he saw the helicopter as "parts began to fall off," it impacted the ground, and then "blew up into flames."

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, issued May 30, 2007; however he did not have a Certificated Flight Instructor rating. His most recent second-class medical certificate was issued on February 7, 2008.

According to the pilot’s logbook, he had accumulated 542 total helicopter flight hours, 433.9 flight 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

Accident Helicopter Information

The helicopter, a Robinson R22 Beta II, serial number 3084, was registered to and operated by Maintenance Services LLC, Rocky Point, North Carolina. It was a two-seat, single main rotor, single-engine helicopter that was constructed primarily of metal and equipped with skid type landing gear and was manufactured in February, 2000. The helicopter was powered by a Lycoming O-360-J2A engine, serial number, L-37378-36A. The maximum gross weight of the helicopter was 1,370 pounds. The helicopter was issued a standard airworthiness certificate on May 11, 2000 and was registered to the owner on February 12, 2007.

Maintenance Information

The helicopter’s most recent annual inspection was completed on December 14, 2007. At the time of the inspection, the total aircraft time was 1,389 total hours of operation and was inspected in accordance with manufacturer's maintenance manual checklist. The engine’s most recent inspection, a 100-hour inspection, was completed on October 13, 2007 and was in accordance to the Robinson and Lycoming Maintenance Manuals. The last maintenance accomplished on the accident helicopter was on March 6, 2008, and consisted of an engine oil and oil filter replacement. This item was accomplished by the accident pilot and the helicopter hours were recorded in the logbook as 1,461 total hours.

METEOROLOGICAL INFORMATION

The 0953 recorded weather at ILM, located approximately 8 miles north of the accident site included winds from 230 degrees at 4 knots, visibility 10 miles, clear skies, temperature 17 degrees C, dew point 4 degrees C, and an altimeter setting of 30.03 inches of mercury.

WRECKAGE AND IMPACT INFORMATION

The helicopter impacted the ground in an open lot approximately 3 feet from several storage trailers. The helicopter displayed impact damage and post impact fire damage. The debris path was on a heading of 342 degrees and the helicopter came to rest on a heading of approximately 140 degrees. The main wreckage consisted of the fuselage, main rotor assembly, tail boom, and tail rotor. The tail cone was separated from the fuselage at a right angle and no leading edge damage was found on the tail rotor blades. Several pieces of the main rotor blade, the empennage, and the helicopter beacon were co-located approximately 350 feet to the south of the main wreckage. The wreckage was examined at the accident site and then recovered to a secure facility at ILM for further examination.

Examination of the helicopter revealed the two main rotor blades exhibited spanwise coning. One of the main rotor blades was missing a section of the trailing edge that measured approximately 6 inches chordwise by 40 inches spanwise starting about 26 inches from the blade hub. The other main rotor blade was missing a section of the trailing edge that measured approximately 6 inches chordwise by 61 inches spanwise starting about 24 inches from the blade hub. One of the sections exhibited an impression, consistent in shape, to the leading edge of the vertical stabilizer. The main rotor system was rotated through the main gear box. The drive belts between the engine and transmission were not identified in the burnt wreckage. The empennage, which consists of the vertical and horizontal stabilizer, was detached from the aft bulkhead of the tailcone.

The intermediate flex plate exhibited evidence of distortion and crumpling and the intermediate flex coupler was separated from both yokes. The tail rotor drive shaft damper bearing housing was disconnected from the bearing. The bearing was in place on the drive shaft and was able to rotate in place.

The interior of the tail cone displayed signs of rotational scoring around the entire circumference. The electrical wires had been pulled through the grommets and the push/pull tube was wrapped around the drive shaft. The tail rotor gear box rotated smoothly and the pitch control bell crank support was separated from the gearbox.

The engine crankshaft was rotated using the cooling fan and continuity of the crankshaft to the rear gears and to the valve train was confirmed. Thumb compression and suction was produced on cylinders 1, 3, and 4. Cylinder number 2 produced minimal compression and further examination revealed the intake valve springs were compressed to a height of 1.4 to 1.5 inches but were unbroken. Both the inner and outer springs were discolored consistent with thermal damage. Cylinder number 2 was removed from the crankcase and no damage was noted to the intake or exhaust valves, cylinder wall, piston, or connecting rod. The interior of all cylinders where inspected using a lighted boroscope; no anomalies were found. The carburetor bowl was separated from its upper housing and was approximately 2 feet from the front of the engine. The main fuel nozzle was broken off and the fuel lines were separated. The mixture control cable was detached but was in the full rich mixture position. The throttle control rod remained attached to the throttle control arm but was separated from the throttle control forward of the firewall. The throttle plate was found about 3/4 fully open. The spark plugs were dark gray in color and the electrodes were intact. The carburetor fuel inlet screen exhibited thermal damage but was free of debris. The oil cooler and hoses were damaged but oil was visible throughout the engine. The engine oil filter paper element was charred. No metallic debris was noted on the oil filter element or the oil suction screen. The magnetos had thermal damage and were unable to be tested.

Examination of the instrument panel revealed the engine rpm needle in approximately the high limit position and the rotor rpm needle in the low limit position. The ignition key position was unable to be determined due to thermal and impact damage.

MEDICAL AND PATHOLOGICAL INFORMATION

The Chief Medical Examiner of North Carolina performed an autopsy on the pilot on March 14, 2008. The reported cause of death was blunt trauma.

Toxicological testing was performed post mortem at the FAA’s Bioaeronautical Sciences Research Laboratory, Oklahoma City, Oklahoma. The tests were negative for carbon monoxide, cyanide, ethanol, and drugs, legal or illegal.

TESTS AND RESEARCH

Push-Pull Tube and Clutch Assembly Materials Examination

The National Transportation Safety Board's 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 fractured surfaces were consistent with overstress separation as a result of the accident. There were no signs of any mechanical malfunctions.

Robinson Helicopter Company published a Safety Notice (SN-36), Overspeeds During Liftoff, which states in part, "…overspeeds caused a tail rotor drive shaft vibration which led to immediate failure of shaft and tailcone… damper is not effective above 120% RPM."

Foreign accident investigations

The Australian Accident Investigation Branch (AAIB) has tested and documented the results of third 'whirl' modes, The most extensive testing done was on a Robinson R 44 helicopter, incident reference number EW/C2003/07/02, which occurred on July 9, 2003, and a R22 Beta, accident reference number EW/C2000/9/3, which occurred on September 13, 2000. The subsequent investigation revealed "that inorder to achieve an overspeed condition created in a 3rd 'whirl' mode there were two possible scenarios found. Either the pilot would have had to open the throttle at flat main rotor blade pitch with the collective lever fully down, or when raising the collective lever the pilot prevented the throttle from winding back under the influence of the governor. As with many long shafts, at certain drive shaft rpm a 'whirl' mode can be induced. This can result in whipping of the shaft and can lead to possible shaft distortion and subsequent physical damage. A damper bearing is installed on the R22 tail rotor drive shaft to damp out the first and second 'whirl' modes. It does not, however, prevent whipping in the third 'whirl' mode."

The 'whirl' modes on the R22 occur at the following engine RPM:

1st - 15.2 % main rotor RPM 2nd - 60.6% main rotor RPM 3rd – 132.0 % main rotor RPM

The first two 'whirl' modes do not occur in flight as they are below the normal main rotor rpm operating range. The third 'whirl' mode will occur if an overspeed occurs; the manufacturer's maximum operating main rotor rpm limitation is 102%.

ADDITIONAL INFORMATION

The helicopter was released to a representative for the estate of the pilot on October 10, 2008.

(c) 2009-2011 Lee C. Baker. For informational purposes only.