Thursday, February 23, 2017

Rotorway Talon A600, N220AF: Accident occurred March 14, 2015 in Indian Lake Estates, Polk County, Florida

The National Transportation Safety Board did not travel to the scene of this accident.

Additional Participating Entities: 
Federal Aviation Administration / Flight Standards District Office; Orlando, Florida 
Rotorway; Phoenix, Arizona 
Bearing Manufacturer; Akron, Ohio

Aviation Accident Final Report -  National Transportation Safety Board: https://app.ntsb.gov/pdf

Docket And Docket Items - National Transportation Safety Board:   https://dms.ntsb.gov/pubdms

Aviation Accident Data Summary - National Transportation Safety Board: https://app.ntsb.gov/pdf

http://registry.faa.gov/N220AF

NTSB Identification: ERA15LA155
14 CFR Part 91: General Aviation
Accident occurred Saturday, March 14, 2015 in Indian Lake Estates, FL
Probable Cause Approval Date: 02/13/2017
Aircraft: RICHARD FUIST ROTORWAY TALON, registration: N220AF
Injuries: 1 Minor.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The student pilot, who was the owner and builder of the experimental amateur-built helicopter, stated that he performed some adjustments to the main rotor blade track and balance and then adjusted the slider ball adjustment collar, located in the rotor hub on the swashplate assembly, on the morning of the accident flight. After making the adjustment, the student conducted an uneventful test flight in the airport traffic pattern, and he then decided to depart on his planned cross-country flight. While approaching to land at his destination, the student felt increasing left cyclic pressure, which increased as the helicopter descended. The student stated that he did not have any further recollection of the accident. A witness reported that the helicopter rolled left about 25 ft above ground level, impacted the ground, and then came to rest on its right side.

Postaccident examination of the helicopter revealed no evidence of preexisting mechanical malfunctions or anomalies. According to the helicopter kit manufacturer, cyclic stiffness and increased cyclic pressure can be caused by worn elastomeric bearings or an incorrectly adjusted slider ball collar. However, a detailed examination of the elastomeric bearings revealed that they were within manufacturer specifications for torsional stiffness and lateral bulge. Although a postaccident hover flight test conducted by the manufacturer showed that an overtightened slider ball adjustment collar can lead to increased left cyclic pressure, postaccident measurements taken by the pilot indicated that the slider ball adjustment was also within manufacturer specifications. The reason for the increased left cyclic pressure could not be determined.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
A loss of helicopter control following an uncommanded increased left cyclic pressure during landing for reasons that could not be determined because postaccident examination of the helicopter revealed no evidence of any mechanical malfunctions or anomalies.

On March 14, 2015, about 1400 eastern daylight time, an experimental amateur-built Rotorway 162F helicopter, N220AF, was substantially damaged during an off-airport landing near Indian Lake Estates, Florida. The student pilot was not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the personal flight, which departed Winter Haven's Gilbert Airport (GIF), Winter Haven, Florida, at 1330. The flight was conducted under the provisions of Title 14 Code of Federal Regulations Part 91.

The student pilot, who was also the owner and builder of the helicopter, stated that he had performed adjustments to the main rotor blade tracking and balancing on the morning of the accident. A hover test of the helicopter revealed no anomalies, but the pilot stated that during the subsequent flight around the airport traffic pattern, the lead/lag of the blades was "off the chart" according to his digital balancer. The pilot landed the helicopter and attempted to contact an acquaintance who was familiar with the helicopter make and model, but was not able to reach him. The pilot elected to make no further blade adjustments until he could consult his acquaintance, and instead chose to adjust the slider ball adjustment collar, located in the rotor hub on the swashplate assembly. He stated that he followed the kit manufacturer's maintenance instructions for the adjustment, and that during a test flight following the adjustment, "everything felt fine." The pilot then departed on a 24 nautical mile flight.

The pilot stated that he experienced no anomalies during the accident flight. While approaching to land at his destination, about 500 feet above ground level (agl), the pilot felt a left cyclic pressure that increased as the helicopter descended. The pilot could not fully recall the accident sequence, but a witness stated that the helicopter rolled to the left at an altitude of approximately 25 feet agl, the rotor blades impacted the ground. The helicopter then rolled over and came to rest on its right side.

Postaccident examination of the helicopter by Federal Aviation Administration (FAA) inspectors revealed that it sustained substantial damage to the tail boom and fuselage. During the examination, the inspectors determined that the elastomeric thrust bearings exhibited an abnormal amount of wear. The inspectors confirmed cyclic control continuity from the cockpit to the rotor blades and traced collective control from the cockpit to the rotor blades through the swashplate, which did not display any abnormalities. Both main rotor blades remained intact: one blade was bent at a 45-degree angle and the other blade was bent opposite the direction of rotation.

The 1347 automated weather observation at an airport located about 22 nm west of the accident site included winds from 180 degrees at 15 knots with gusts to 20 knots; visibility 10 statute miles, a broken cloud layer at 4,000 feet; temperature 28 degrees C; dew point 16 degree C; and an altimeter setting of 30.11 inches of mercury.

The pilot held a student pilot and FAA third-class medical certificate, which was issued in August 2014. He reported that he had accumulated about 55 total hours of flight experience, all of which were in helicopters. At the time of the accident, the pilot had accrued about 23 total flight hours in the accident helicopter make and model, with about 20 hours, including 16 hours of dual instruction in the two weeks that preceded the accident.

The two-place helicopter was equipped with a Rotorway RI600N 150 hp reciprocating engine, and was assembled by the student pilot from a kit with assistance from a mechanic. The helicopter was equipped with a two-blade main rotor and a two-blade tail rotor. The airworthiness certificate was issued in November 14, 2014. At the time of the accident, the helicopter had accumulated approximately 40 total flight hours; 15 hours of which involved hover taxi tests that were not documented in the pilot's personal flight logbook.

The two elastomeric bearings and the thrust blocks were submitted to the NTSB Materials Laboratory for detailed examination. A review of the bearings showed no anomalous wear scar patterns on any of the bearing surfaces; however, microscope images revealed the presence of elastomer extrusion at the inside and outside diameter surfaces. The thrust blocks did not display any wear scar patterns within the counter bores and associated sleeves. The bearings were subsequently sent to the manufacturer and evaluated for torsional stiffness and lateral bulge under the supervision of an FAA inspector. The torsional stiffness between both bearings measured approximately 9.84 lbf-inch/degree. The highest lateral bulge measurement for the bearings was 0.0190. According to the manufacturer's specifications, the torsional stiffness should measure between 10 – 13 pounds of force (lbf) inch/degree and the lateral bulge should be less than 0.040 inches.

According to the bearing manufacturer, the functional test results on the accident bearings were consistent with the results of new bearings. The manufacturer further stated that a blackened appearance of the outer surface resulting from micro-scaled extrusion will show during the first 23 flight hours under normal thrust loads and oscillations, but "has no affect upon function."

According to the maintenance manual, the slider ball adjustment collar can produce a feedback through the cyclic controls if the collar is not correctly adjusted. This will cause the cyclic to travel in any one direction independent of any input from the pilot. A representative of the kit manufacturer stated that if the slider ball adjustment collar set screws are not secured, the shaft will overtighten the collar during flight, which may increase cyclic pressure. Following the accident, the manufacturer performed a hover test flight to determine the impact of an overtightened adjustment collar on control function. The pilot experienced hard left cyclic pressure during the hover test.

After the accident, the student pilot measured the slider ball adjustment collar at the request of the NTSB investigator-in-charge. He initially verified that the set screws were tight and then marked the position of the adjustment collar with a black pen. The student pilot then loosened the set screws and tightened the collar until it was "snug." He marked the collar position again with a black pen and then loosened the set screws and the adjustment collar. He noted that the black marks were approximately one half inch apart, consistent with the kit manufacturer's maintenance instructions.

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