# NTSB GAA16CA201: Helicycle/Morrisey RR RM-1, N867TV, Denver, CO, April 22, 2016 - Type: NTSB accident investigation - Classification: Accident · Minor injuries · Data collection · Final report - Date: April 22, 2016, 16:00 local (22:00 UTC) - Place: Denver, CO - Coordinates: 39.784168, -104.537498 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=39.7842&lon=-104.5375&mi=10 - Phase of flight: [Approach](https://openairdocs.org/ntsb-phases/500) (OpenAirDocs' grouping) - Defining event: [Approach-VFR pattern final: Loss of tail rotor effectiveness](https://openairdocs.org/ntsb-events/242) - Highest injury: Minor injuries - Injuries: 1 minor - Status: Completed, report July 14, 2016 - Report: Approved by Office Director - NTSB office: General Aviation Accidents - Parties: FAA - NTSB case key (mKey): 93068 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=GAA16CA201 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/93068/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=93068 - Page: https://openairdocs.org/ntsb/GAA16CA201 ## Probable cause The pilot's failure to maintain control of the helicopter yaw while operating in conditions conducive to loss of tail rotor effectiveness, resulting in an uncommanded rapid right yaw and ground impact. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Performance/control parameters: yaw control](https://openairdocs.org/ntsb-findings/01062024): Aircraft › Aircraft oper/perf/capability · Not attained/maintained (probable cause); cases with it: [Helicycle/Morrisey R R RM-1, 1 case](https://openairdocs.org/ntsb-findings/01062024/cases.md?model=05620U7), [All aircraft, 149 cases](https://openairdocs.org/ntsb-findings/01062024/cases.md) - [Use of equip/info: aircraft control](https://openairdocs.org/ntsb-findings/02063040): Personnel issues › Task performance · Pilot (probable cause); cases with it: [Helicycle/Morrisey R R RM-1, 1 case](https://openairdocs.org/ntsb-findings/02063040/cases.md?model=05620U7), [All aircraft, 9,295 cases](https://openairdocs.org/ntsb-findings/02063040/cases.md) - [Wind: tailwind](https://openairdocs.org/ntsb-findings/03034015): Environmental issues › Conditions/weather/phenomena · Awareness of condition; cases with it: [Helicycle/Morrisey R R RM-1, 1 case](https://openairdocs.org/ntsb-findings/03034015/cases.md?model=05620U7), [All aircraft, 594 cases](https://openairdocs.org/ntsb-findings/03034015/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Approach-VFR pattern final: Loss of tail rotor effectiveness](https://openairdocs.org/ntsb-events/242) (defining event); cases with it: [Helicycle/Morrisey R R RM-1, 1 case](https://openairdocs.org/ntsb-events/242/sequence.md?model=05620U7), [All aircraft, 100 cases](https://openairdocs.org/ntsb-events/242/sequence.md) - [Uncontrolled descent: Collision with terr/obj (non-CFIT) ](https://openairdocs.org/ntsb-events/470); cases with it: [Helicycle/Morrisey R R RM-1, 1 case](https://openairdocs.org/ntsb-events/470/sequence.md?model=05620U7), [All aircraft, 10,189 cases](https://openairdocs.org/ntsb-events/470/sequence.md) ## Analysis According to the pilot, after a local flight in his experimental amateur built helicopter, he rejoined the pattern at the towered airport that he departed thirty minutes prior. The runway in use was 08, and the pilot requested to land on runway 17 in order to practice hovering. The pilot reported that he executed multiple approaches to runway 17, and requested a wind check from the tower. During the accident approach tower reported, "Wind 090 at 03." The pilot affirmed that as he made his turn from base to final his airspeed was slow. He reported that during his descent at slow airspeed, with a direct, left crosswind, the helicopter yawed right. He asserted that he lowered the collective, and applied forward cyclic which had no effect on the uncommanded rapid right yaw. Finally, the pilot reported that "application of left pedal throughout made no difference in correcting the aircraft heading." The helicopter made several 360 degree turns and just prior to the helicopter ground impact; the pilot reported that he increased the collective. The helicopter sustained substantial damage to the frame and windscreen. The pilot reported that the accident occurred about 1600 mountain daylight time (MDT). The Automated Terminal Information Service reported that wind conditions at 1547 (MDT) were 120 degrees true at 10 knots. The pilot remarked that after exiting the helicopter, as he walked away from the wreckage, he noticed that the wind was variable and gusting. The pilot reported that there were no mechanical failures or anomalies with the airplane prior to or during the flight that would have prevented normal flight operation. According the Federal Aviation Administration (FAA) Helicopter Flying Handbook (FAA-8083-21A) section describing Loss of Tail Rotor Effectiveness (LTE), and more specifically FAA Advisory Circular (AC) 90-95 Unanticipated Rapid Right Yaw (pg. 1, para. 4.a.): LTE is a critical; low-speed aerodynamic flight characteristic which can result in an uncommanded rapid yaw rate which does not subside of its own accord and, if not corrected, can result in the loss of aircraft control. 7. b. Although specific wind azimuths are identified for each region, the pilot should be aware that the azimuths shift depending on the ambient conditions. The regions do overlap. The most pronounced thrust variations occur in these overlapping areas. c. These characteristics are present only at airspeeds less than 30 knots and apply to all single rotor helicopters. Flight test data has verified that the tail rotor does not stall during this period. d. The aircraft characteristics and relative wind azimuth regions are: (1) Main rotor disc vortex interference (285" to 315"). (See figure 1.) (a) Winds at velocities of about 10 to 30 knots from the left front will cause the main rotor vortex to be blown into the tail rotor by the relative wind. The effect of this main rotor disc vortex is to cause the tail rotor to operate in an extremely turbulent environment.(3) Tail rotor vortex ring state (210" to 330"). (a) Winds within this region will result in the development of the vortex ring state of the tail rotor. As the inflow passes through the tail rotor, it creates a tail rotor thrust to the left. A left crosswind will oppose this tail rotor thrust. This causes the vortex ring state to form, which causes a nonuniform, unsteady flow into the tail rotor. The vortex ring state causes tail rotor thrust variations which result in yaw deviations. The net effect of the unsteady flow is an oscillation of tail rotor thrust. This is why rapid and continuous pedal movements are necessary when hovering in left crosswind. ## Factual narrative According to the pilot, after a local flight in his experimental amateur built helicopter, he rejoined the pattern at the towered airport that he departed thirty minutes prior. The runway in use was 08, and the pilot requested to land on runway 17 in order to practice hovering. The pilot reported that he executed multiple approaches to runway 17, and requested a wind check from the tower. During the accident approach tower reported, "Wind 090 at 03." The pilot affirmed that as he made his turn from base to final his airspeed was slow. He reported that during his descent at slow airspeed, with a direct, left crosswind, the helicopter yawed right. He asserted that he lowered the collective, and applied forward cyclic which had no effect on the uncommanded rapid right yaw. Finally, the pilot reported that "application of left pedal throughout made no difference in correcting the aircraft heading." The helicopter made several 360 degree turns and just prior to the helicopter ground impact; the pilot reported that he increased the collective. The helicopter sustained substantial damage to the frame and windscreen. The pilot reported that the accident occurred about 1600 mountain daylight time (MDT). The Automated Terminal Information Service reported that wind conditions at 1547 (MDT) were 120 degrees true at 10 knots. The pilot remarked that after exiting the helicopter, as he walked away from the wreckage, he noticed that the wind was variable and gusting. The pilot reported that there were no mechanical failures or anomalies with the airplane prior to or during the flight that would have prevented normal flight operation. According the Federal Aviation Administration (FAA) Helicopter Flying Handbook (FAA-8083-21A) section describing Loss of Tail Rotor Effectiveness (LTE), and more specifically FAA Advisory Circular (AC) 90-95 Unanticipated Rapid Right Yaw (pg. 1, para. 4.a.): LTE is a critical; low-speed aerodynamic flight characteristic which can result in an uncommanded rapid yaw rate which does not subside of its own accord and, if not corrected, can result in the loss of aircraft control. 7. b. Although specific wind azimuths are identified for each region, the pilot should be aware that the azimuths shift depending on the ambient conditions. The regions do overlap. The most pronounced thrust variations occur in these overlapping areas. c. These characteristics are present only at airspeeds less than 30 knots and apply to all single rotor helicopters. Flight test data has verified that the tail rotor does not stall during this period. d. The aircraft characteristics and relative wind azimuth regions are: (1) Main rotor disc vortex interference (285" to 315"). (See figure 1.) (a) Winds at velocities of about 10 to 30 knots from the left front will cause the main rotor vortex to be blown into the tail rotor by the relative wind. The effect of this main rotor disc vortex is to cause the tail rotor to operate in an extremely turbulent environment.(3) Tail rotor vortex ring state (210" to 330"). (a) Winds within this region will result in the development of the vortex ring state of the tail rotor. As the inflow passes through the tail rotor, it creates a tail rotor thrust to the left. A left crosswind will oppose this tail rotor thrust. This causes the vortex ring state to form, which causes a nonuniform, unsteady flow into the tail rotor. The vortex ring state causes tail rotor thrust variations which result in yaw deviations. The net effect of the unsteady flow is an oscillation of tail rotor thrust. This is why rapid and continuous pedal movements are necessary when hovering in left crosswind. ## Aircraft - Registration: [N867TV](https://openairdocs.org/deregistered/N867TV-2019-05-06), registration cancelled 2019-05-06, S/N 007, built 2006 (OpenAirDocs) - Reported make and model: HELICYCLE/MORRISEY RR RM-1 - Registry model: [Helicycle/Morrisey R R RM-1](https://openairdocs.org/model/helicycle-morrisey-r-r-rm-1) (registry code 05620U7) (OpenAirDocs) - Registry engine: [Amateur-built UNKNOWN ENG](https://openairdocs.org/engine/amateur-built-unknown-eng) (registry code 99999) (OpenAirDocs) - Category: Helicopter, amateur-built - Serial number: 007 - Year built: 2006 - Airframe hours: 188.7 - Engines: Solar T62-T32 90 horsepower turbo shaft - Damage: Substantial damage - Flight: Personal, Part 91 - Operator: TurbineV LLC. - Registered owner: TurbineV LLC. - Airworthiness certificate: Special, Experimental (Special) - Departed: FTG, Denver, CO - Destination: FTG, Denver, CO - Airport: FTG, Front Range - Equipment: None ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 53; injuries: minor; private; medical: class 2, with waivers/limitations; last flight review November 8, 2014; seat: single; flight hours: 229 total, 8 in this make and model, 117 as pilot in command, 38 in the last 90 days, 1 in the last 30 days ## Weather - Conditions: Visual (VMC), Day - Wind: 120° at 10 knots - Visibility: 50 statute miles - Temperature: 75 °F, dew point 28 °F - Altimeter: 29.98 inHg - Observed at: KFTG ## 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 20160422003879A](https://openairdocs.org/incident/20160422003879A), Apr 22, 2016: Helicycle/Morriesey R R RM-1, Watkins, CO, Substantial damage. While on approach at Front Range Airport to runway 17, aircraft yawed right and began to spin. Aircraft landed in a spin and rolled over on its left side. ## Docket (2 files) The files NTSB released with the investigation on July 11, 2016, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=93068. 2.3 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 1.9 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40442208&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Master.PDF - Photo (Courtesy of FAA) (item 2, .PDF, 1 photo, 464 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40442209&FileExtension=.PDF&FileName=Photo%20(Courtesy%20of%20FAA)-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.