# NTSB WPR16LA075: Robinson Helicopter R66, N266RH, Torrance, CA, February 23, 2016 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: February 23, 2016, 11:45 local (19:45 UTC) - Place: Torrance, CA - Coordinates: 33.802501, -118.338607 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=33.8025&lon=-118.3386&mi=10 - Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping) - Defining event: [Maneuvering: Miscellaneous/other](https://openairdocs.org/ntsb-events/900) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report June 20, 2017 - Report: Approved by Office Director - NTSB office: Western Pacific Region - Parties: Robinson Helicopter, FAA FSDO - NTSB case key (mKey): 92758 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR16LA075 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/92758/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=92758 - Page: https://openairdocs.org/ntsb/WPR16LA075 ## Probable cause 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. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Not determined](https://openairdocs.org/ntsb-findings/05000000): Not determined › Not determined · Unknown/Not determined (probable cause); cases with it: [Robinson Helicopter R66, 3 cases](https://openairdocs.org/ntsb-findings/05000000/cases.md?model=7640130), [All aircraft, 2,247 cases](https://openairdocs.org/ntsb-findings/05000000/cases.md) - [Terrain: wet/muddy terrain](https://openairdocs.org/ntsb-findings/03021035): Environmental issues › Physical environment · Not specified; cases with it: [Robinson Helicopter R66, 2 cases](https://openairdocs.org/ntsb-findings/03021035/cases.md?model=7640130), [All aircraft, 110 cases](https://openairdocs.org/ntsb-findings/03021035/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Maneuvering: Miscellaneous/other](https://openairdocs.org/ntsb-events/900) (defining event); cases with it: [Robinson Helicopter R66, 3 cases](https://openairdocs.org/ntsb-events/900/sequence.md?model=7640130), [All aircraft, 1,556 cases](https://openairdocs.org/ntsb-events/900/sequence.md) - [Autorotation: Miscellaneous/other](https://openairdocs.org/ntsb-events/900); cases with it: [Robinson Helicopter R66, 3 cases](https://openairdocs.org/ntsb-events/900/sequence.md?model=7640130), [All aircraft, 1,556 cases](https://openairdocs.org/ntsb-events/900/sequence.md) - [Landing-flare/touchdown: Abrupt maneuver](https://openairdocs.org/ntsb-events/270); cases with it: [Robinson Helicopter R66, 3 cases](https://openairdocs.org/ntsb-events/270/sequence.md?model=7640130), [All aircraft, 346 cases](https://openairdocs.org/ntsb-events/270/sequence.md) ## Analysis 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. ## Factual narrative 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. 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. 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 theengine 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. ## Aircraft - Registration: [N266RH](https://openairdocs.org/aircraft/N266RH), registered now, S/N 0002, built 2009 (OpenAirDocs) - Reported make and model: ROBINSON HELICOPTER CO R66 (NO SERIES) - Registry model: [Robinson Helicopter R66](https://openairdocs.org/model/robinson-helicopter-r66) (registry code 7640130) (OpenAirDocs) - Registry engine: [Rolls-Royce 250-C300/A1](https://openairdocs.org/engine/rolls-royce-250-c300-a1) (registry code 54232, turbo-shaft) (OpenAirDocs) - Category: Helicopter - Serial number: 0002 - Year built: 2009 - Airframe hours: 400.04 - Engines: Rolls-Royce 250-C300/A1 300 horsepower turbo shaft - Damage: Substantial damage - Flight: Flight test, Part 91 - Operator: Robinson Helicopter Co - Registered owner: Robinson Helicopter Co - Airworthiness certificate: Special, Experimental (Special) - Last inspection: Annual, October 15, 2015 - Departed: TOA, Torrance, CA - Destination: TOA, Torrance, CA - Airport: TOA, Zamperini Field - Equipment: Auto-pilot, Electronic primary flight display ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 45; injuries: none; flight instructor, commercial; airplane ratings: single-engine sea; instrument ratings: airplane, helicopter; medical: class 2, with waivers/limitations; last flight review April 23, 2014; seat: right; flight hours: 1,750 total, 200 in this make and model, 1,650 as pilot in command, 30 in the last 90 days, 15 in the last 30 days ## Weather - Conditions: Visual (VMC), Day - Wind: calm - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 84 °F, dew point 36 °F - Altimeter: 30.01 inHg - Observed at: KTOA ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Accident 20160223007729A](https://openairdocs.org/incident/20160223007729A), Feb 23, 2016: Robinson Helicopter Co R66, Torrance, CA, Substantial damage. Robinson R66 helicopter was being flown by Robinson test pilot [privacy data omitted] to put some time on systems that Robinson was testing. After liftoff and… ## Docket (12 files) The files NTSB released with the investigation on April 10, 2017, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=92758. 6.2 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 258 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40454451&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Master.PDF - FAA Statements (item 2, .PDF, 2.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40450927&FileExtension=.PDF&FileName=FAA%20Statements-Master.PDF - NTSB Engine Examination (item 3, .PDF, 211 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40450928&FileExtension=.PDF&FileName=NTSB%20Engine%20Examination-Master.PDF - Flight Export Data (item 4, .PDF, 760 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40450929&FileExtension=.PDF&FileName=Flight%20Export%20Data-Master.PDF - Rolls-Royce Operating Manual Excerpt Use Approval (item 5, .PDF, 112 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40450930&FileExtension=.PDF&FileName=Rolls-Royce%20Operating%20Manual%20Excerpt%20Use%20Approval-Master.PDF - Rolls-Royce Operating Manual Excerpt (item 6, .PDF, 511 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40450931&FileExtension=.PDF&FileName=Rolls-Royce%20Operating%20Manual%20Excerpt-Master.PDF - Manufacturer's Explanation of the Failure (item 7, .PDF, 86 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40450932&FileExtension=.PDF&FileName=Manufacturer%27s%20Explanation%20of%20the%20Failure-Master.PDF - Purpose of Flight (item 8, .PDF, 423 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40450933&FileExtension=.PDF&FileName=Purpose%20of%20Flight-Master.PDF - Statement of Party Representatives to NTSB Investigation (item 9, .PDF, 207 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40450934&FileExtension=.PDF&FileName=Statement%20of%20Party%20Representatives%20to%20NTSB%20Investigation-Master.PDF - Release of Aircraft Wreckage, NTSB Form 6120.15 (item 10, .PDF, 138 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40450935&FileExtension=.PDF&FileName=Release%20of%20Aircraft%20Wreckage,%20NTSB%20Form%206120.15-Master.PDF - FAA Photos of a Sprag Clutch (item 11, .PDF, 2 photos, 416 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40450936&FileExtension=.PDF&FileName=FAA%20Photos%20of%20a%20Sprag%20Clutch-Master.PDF - Photos (item 12, .PDF, 4 photos, 926 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40450937&FileExtension=.PDF&FileName=Photos-Master.PDF From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.