Wednesday, February 24, 2016

Robinson R66, Robinson Helicopter Co., N266RH: Accident occurred February 23, 2016 at Zamperini Field (KTOA), Torrance, Los Angeles County, California

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

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

Additional Participating Entities:

Federal Aviation Administration / Flight Standards District Office;  Long Beach, California 
Robinson Helicopter; Torrance, California 

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


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


ROBINSON HELICOPTER CO: http://registry.faa.gov/N266RH

NTSB Identification: WPR16LA075
14 CFR Part 91: General Aviation
Accident occurred Tuesday, February 23, 2016 in Torrance, CA
Probable Cause Approval Date: 06/20/2017
Aircraft: ROBINSON HELICOPTER CO R66, registration: N266RH
Injuries: 1 Uninjured.

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 commercial pilot was performing company flight testing in the helicopter. After performing an air taxi and a hovering autorotation, the pilot conducted a simulated maximum performance takeoff. About 200 ft above ground level, the pilot heard a noise and felt a momentary helicopter vibration. He subsequently performed a precautionary autorotation to a grass area on airport property. The pilot stated that the helicopter had forward speed during the landing and that the grass was soft; as a result, the helicopter entered a fore-aft rocking motion after touchdown, and the main rotor contacted the tail boom, resulting in substantial damage. 

Postaccident review of data from the engine monitoring unit revealed no anomalies, and an examination of the helicopter revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation; therefore, the reason for the noise and vibration could not be determined. 

The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
A vibration of the helicopter, which resulted in an autorotation to soft terrain and subsequent impact of the tail boom with the main rotor. The reason for the vibration could not be determined because postaccident examination revealed no malfunctions or anomalies that would have precluded normal operation.

HISTORY OF FLIGHT

On February 23, 2016, about 1145 Pacific standard time, a Robinson R66, N266RH, sustained substantial damage to the tailboom following a precautionary autorotation at Zamperini Field Airport (TOA), Torrance, California. The pilot, the sole occupant, was not injured. The experimental (research and development category) test helicopter was registered to and operated by Robinson Helicopter Company (RHC) as a test flight under the provision of 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and no flight plan was filed for the local flight that originated from TOA at 1145.

The purpose of the flight was to test the auxiliary fuel system, low RPM horn, autopilot, and sprag clutch.

The pilot reported that he had performed a takeoff to a hover, a hover taxi, and one hovering autorotation without incident. He then executed a maximum performance takeoff. About 200 feet above ground level, the pilot heard a noise and felt a momentary helicopter vibration. Subsequently, he performed an autorotation to a grassy area on the airfield. After the helicopter landed in soft grass with forward momentum, it experienced a fore and aft rocking motion, and the main rotor blades contacted the tailboom.

HELICOPTER INFORMATION

The five-seat helicopter, serial number 0002, was manufactured in 2009. The operator reported that the helicopter's maximum gross weight was 2,700 pounds, and it weighed 2,047 at the time of the accident. The helicopter was powered by a 300-horsepower Rolls Royce 250-C300/A1 engine. The last annual maintenance inspection was conducted on October 15, 2015, at the total engine time of 363 hours. The airframe had a total of 400.04 hours at the time of the accident, as it had operated 20 hours since its last maintenance inspection. The engine was examined on March 4, 2016, at RHC, Torrance, California.

TESTS AND RESEARCH

A visual examination of the airframe components was conducted and no anomalies were found. There were no metal particles found in the oil filter and the chip detector. The Engine Monitoring Unit (EMU) data was downloaded and reviewed by a representative from Rolls-Royce. The EMU provided general information about the operation of the engine including time, cycles, faults and any exceedances of engine operating limits. The downloaded data corresponded to the entire accident flight. There were no exceedances noted in the data; however, at the time stamp 32.27.1 the power turbine (N2) peaked at 107.76% and the Torquemeter Oil Pressure (TMOP) peaked at 95.304% (275 ft/lbs). According to the Rolls Royce 300 Operational and Maintenance Manual, the limit for N2 is 110% for 15 seconds, and the torque limit during takeoff is 288 ft/lbs with a maximum transient of 430 ft/lbs. 

With no pre-accident anomalies noted with the engine, the engine was test run on the helicopter through various power settings. No anomalies were noted during the engine exam. The engine data was downloaded after the engine runs, and no faults were noted in the data.

Following the engine run, the sprag clutch was inspected and it was revealed that the sprag clutch had moved between 45-90 degrees from its original position. The sprag clutch was then removed, and it was observed that it took about 550 pounds of torque to loosen the clutch assembly compared to the 300 pounds of torque used to tighten the clutch in the assembly process. The clutch was then inspected, and no anomalies were found. 

A review of the maintenance logbook revealed that the new Revision E sprag clutch had been installed on the helicopter before the accident flight. The Revision E sprag clutch was compared to the previously installed Revision D sprag clutch, and the wear patterns appeared normal and consistent with those observed in the Revision E clutch assembly.

The complete engine report is appended to this accident in the public docket.

The Pilot's Operating Handbook states that a vibration can be an indication of a drive system failure. However, a drive system failure is also accompanied by nose right or left yaw, and a decrease of the rotor RPM while N2 RPM increases.

RHC Safety Notice SN-39, issued in July 2003, stated that an unusual vibration can indicate a main rotor blade crack. However, those vibrations are characterized as severe and the helicopter would be difficult to control.

NTSB Identification: WPR16LA075 
14 CFR Part 91: General Aviation
Accident occurred Tuesday, February 23, 2016 in Torrance, CA
Aircraft: ROBINSON HELICOPTER CO R66, registration: N266RH
Injuries: 1 Uninjured.

This is preliminary information, subject to change, and may contain errors. Any errors in this report will be corrected when the final report has been completed. NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

On February 23, 2016, about 1145 Pacific standard time, a Robinson R66, N266RH, sustained substantial damage following a precautionary autorotation at Zamperini Field airport (TOA), Torrance, California. The pilot, the sole occupant, was not injured. The helicopter was registered to, and operated by, Robinson Helicopter Company under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed, and no flight plan was filed for the local flight that originated from TOA at 1145.

The pilot reported that he was executing a simulated maximum performance takeoff. About 200 feet above ground level, the pilot felt vibrations and subsequently performed an autorotation to an open area. The helicopter impacted the ground and the main rotor blades contacted the tailboom, which resulted in substantial damage.

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