# NTSB WPR19LA194: Bell 47G 3B 1, N3078G, Mosby, MT, July 13, 2019 - Type: NTSB accident investigation - Classification: Accident · Serious injuries · Class 3 · Limited · Final report - Date: July 13, 2019, 14:30 local (20:30 UTC) - Place: Mosby, MT - Coordinates: 47.040832, -107.66055 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=47.0408&lon=-107.6606&mi=10 - Phase of flight: [Landing](https://openairdocs.org/ntsb-phases/550) (OpenAirDocs' grouping) - Defining event: [Landing: Loss of control in flight](https://openairdocs.org/ntsb-events/240) - Highest injury: Serious injuries - Injuries: 2 serious, 1 minor - Status: Completed - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Western Pacific Region - Parties: Helena FSDO, Rolls-Royse Corporation - NTSB case key (mKey): 99890 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR19LA194 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/99890/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=99890 - Page: https://openairdocs.org/ntsb/WPR19LA194 ## Probable cause The pilot’s failure to account for environmental conditions conducive to a loss of tail rotor effectiveness, which resulted in a loss of tail rotor effectiveness and subsequent loss of control. Contributing to the accident was the pilot’s inappropriate application of power during the recovery. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Use of equip/info: aircraft control](https://openairdocs.org/ntsb-findings/02063040): Personnel issues › Task performance · Pilot (probable cause); cases with it: [Bell 47G-3B-1, 6 cases](https://openairdocs.org/ntsb-findings/02063040/cases.md?model=1181028), [All aircraft, 9,295 cases](https://openairdocs.org/ntsb-findings/02063040/cases.md) - [Performance/control parameters: prop/rotor parameters](https://openairdocs.org/ntsb-findings/01062052): Aircraft › Aircraft oper/perf/capability · Not attained/maintained (probable cause); cases with it: [Bell 47G-3B-1, 2 cases](https://openairdocs.org/ntsb-findings/01062052/cases.md?model=1181028), [All aircraft, 182 cases](https://openairdocs.org/ntsb-findings/01062052/cases.md) - [Knowledge: knowledge of meteorologic cond](https://openairdocs.org/ntsb-findings/02032020): Personnel issues › Experience/knowledge · Pilot; cases with it: [Bell 47G-3B-1, 1 case](https://openairdocs.org/ntsb-findings/02032020/cases.md?model=1181028), [All aircraft, 30 cases](https://openairdocs.org/ntsb-findings/02032020/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Landing: Loss of tail rotor effectiveness](https://openairdocs.org/ntsb-events/242); cases with it: [Bell 47G-3B-1, 1 case](https://openairdocs.org/ntsb-events/242/sequence.md?model=1181028), [All aircraft, 100 cases](https://openairdocs.org/ntsb-events/242/sequence.md) - [Landing: Loss of control in flight](https://openairdocs.org/ntsb-events/240) (defining event); cases with it: [Bell 47G-3B-1, 5 cases](https://openairdocs.org/ntsb-events/240/sequence.md?model=1181028), [All aircraft, 5,002 cases](https://openairdocs.org/ntsb-events/240/sequence.md) - [Landing: Collision with terr/obj (non-CFIT) ](https://openairdocs.org/ntsb-events/470); cases with it: [Bell 47G-3B-1, 10 cases](https://openairdocs.org/ntsb-events/470/sequence.md?model=1181028), [All aircraft, 10,189 cases](https://openairdocs.org/ntsb-events/470/sequence.md) ## Analysis The pilot had refueled the helicopter, bringing the total fuel on board to about 58 gallons, and departed with two passengers for a 15-mile flight to a private ranch. After arriving at the destination, the pilot circled the area and determined the wind direction. He established a normal approach path into the wind to land near a building. While about 30 to 40 feet above ground level, the helicopter entered an uncommanded yaw to the right. Despite the pilot’s control inputs, which included application of full left pedal, the helicopter continued to yaw to the right. The pilot attempted to recover and applied forward cyclic to gain airspeed to go-around. The helicopter continued to yaw right and ascended above the building as described by the two passengers and a witness located near the building. During the recovery attempt, the pilot recalled initially lowering the collective when the yaw first occurred, but did not recall raising or lowering it again. The pilot lost control of the helicopter, which subsequently impacted the ground in a silage pit about 250 feet north of the intended landing area. An engine test run and airframe examination revealed no mechanical failures or malfunctions with the helicopter that would have precluded normal operation. During the approach, the helicopter was operating in a high-power demand condition due to high density altitude, high gross weight, and while near the out-of-ground effect boundary and at a slow airspeed. These conditions reduced the amount of yaw control effectiveness available to counter an uncommanded right yaw. Additionally, the pilot’s selected approach path placed the helicopter on the leeward side of a building and likely exposed the helicopter to disturbed air that disrupted the airflow entering the main rotor and tail rotor and initiated the uncommanded right yaw/loss of tail rotor effectiveness. During the recovery attempt, the pilot likely increased the collective while applying full left pedal, which resulted in the ascent described by the passengers and witness. The added power from the increased collective would also have resulted in an increased right yaw rate and the subsequent loss of control. ## Factual narrative On July 13, 2019, about 1430 mountain daylight time, a Bell 47G-3B-1 helicopter, N3078G, was substantially damaged when it was involved in an accident near Mosby, Montana. The pilot and one passenger received serious injuries; one passenger received minor injuries. The helicopter was operated as a Title 14 Code of Federal Regulations Part 91 aerial observation flight. Before departing on the 15-mile flight, the pilot fueled the helicopter, bringing the total fuel quantity to about 58 gallons. After arriving at the destination, the pilot circled the landing area to determine the wind conditions. Concluding that the wind was light and from the west, he entered a normal approach into the wind to land near the building where the helicopter would be stored following the flight. During the approach, the helicopter entered an uncommanded yaw to the right. Despite the pilot’s control inputs, which included full left pedal application, the helicopter continued to yaw to the right. He attempted to recover by applying forward cyclic control to gain airspeed and then perform a go-around. The pilot recalled lowering the collective control when the event first started, but did not recall if he raised or lowered the collective control during the go-around attempt. He stated that the controls felt like they were ineffective and that the helicopter descended straight down and impacted the ground hard. One passenger stated that the helicopter pitched from side to side and then the tail came around twice. He stated that the pilot tried to climb and as the helicopter was going up, it was still spinning. The other passenger recalled that they were approaching the building and the helicopter swung to the right and started to ascend above the building. A witness located near the building reported that the helicopter approached from the east and looked normal until it was about 30 to 40 ft above the ground. He said that the helicopter turned right, then left, and back to the right before it ascended and flew directly over his position. The witness photographed the helicopter as it began to yaw to the right. (see Figure 1.) Figure 1. Photograph of the helicopter as it began the uncommanded right yaw. Photo courtesy of a witness. The helicopter came to rest in a level attitude in a silage pit located about 250 ft north of the intended landing area, at an elevation of 2,856 ft above mean sea level (msl). All major components were found in the small debris area around the helicopter. Postaccident examination of the airframe revealed no preaccident mechanical malfunctions or failures with the helicopter that would have precluded normal operation. The engine was examined and test run at a Rolls-Royce authorized service facility and operated normally, with no mechanical malfunctions or failures that would have precluded normal operation. A review of the pilot’s training records revealed that he had recorded about 1,092 hours of flight experience in reciprocating enginehelicopters. According to the operator, after the pilot was hired, he began training to operate the turbine-powered Bell 47G-3B-1. He received 18 hours of ground instruction, 4 hours of flight training, and an additional 6 hours of solo flight time in the helicopter. He accrued an additional 15.5 flight hours during the aerial observation flights before the accident. An automated weather reporting station located at Lewiston Municipal Airport, about 84 miles west of the accident site, reported wind from 080° at 7 knots, 10 statute miles visibility, clear sky condition, temperature 31°C, dew point temperature 12°C, and an altimeter setting of 30.00 inches of mercury. The calculated density altitude for the accident site about the time of the accident was about 5,406 ft msl. A weather reporting station located about 5 miles northeast of the accident site reported wind from 160° at 7 knots, temperature 31°C, dewpoint temperature 15°C. The Federal Aviation Administration Helicopter Flying Handbook (FAA-H-8083-21B) states the following regarding loss of tail rotor effectiveness (LTE), also referred to as “uncontrolled right yaw”: LTE is a condition that occurs when the flow of air through a tail rotor is altered in some way, by altering the angle or speed at which the air passes through the rotating blades of the tail rotor disk. To help reduce the onset of LTE, follow these steps: Avoid OGE [out of ground effect] operations and high-power demand situations below airspeeds of 30 knots at low altitudes. A loss of translational lift results in an unexpected high-power demand and an increased antitorque requirement. Be aware that if a considerable amount of left pedal is being maintained, a sufficient amount of left pedal may not be available to counteract an unanticipated right yaw. Be alert to changing wind conditions, which may be experienced when flying along ridge lines and around buildings. Recovery technique (Uncontrolled Right Yaw). If a sudden unanticipated right yaw occurs, the following recovery technique should be performed. Apply full left pedal. Simultaneously, apply forward cyclic control to increase speed. If altitude permits, reduce power… If the rotation cannot be stopped and ground contact is imminent, an autorotation may be the best course of action. ## Aircraft - Registration: [N3078G](https://openairdocs.org/deregistered/N3078G-2022-03-05), registration cancelled 2022-03-05, S/N 2925, built 1964 (OpenAirDocs) - Reported make and model: BELL 47G 3B 1 - Registry model: [Bell 47G-3B-1](https://openairdocs.org/model/bell-47g-3b-1) (registry code 1181028) (OpenAirDocs) - Registry engine: [Allison 250 SER 250HP](https://openairdocs.org/engine/allison-250-ser-250hp) (registry code 03003, turbo-prop) (OpenAirDocs) - Category: Helicopter - Serial number: 2925 - Year built: 1964 - Airframe hours: 7328.1 - Engines: Rolls-Royce 250-C20B 420 horsepower turbo shaft - Damage: Substantial damage - Flight: Aerial observation, Part 91 - Airworthiness certificate: Standard, Normal - Last inspection: Annual, April 16, 2019, 450.9 hours before - Departed: Benzien, MT - Destination: Mosby, MT - Flight plan: Company VFR - Equipment: ADS-B, Satellite tracking device ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 31; injuries: serious; flight instructor, commercial; instrument ratings: helicopter; medical: class 1, without waivers/limitations; seat: left; restraint: 4-point; flight hours: 1,125 total, 36 in this make and model, 1,037 as pilot in command ## Weather - Conditions: Visual (VMC), Day - Wind: 160° at 7 knots - Visibility: 10 statute miles - Temperature: 88 °F, dew point 59 °F - Altimeter: 30.00 inHg - Observed at: LWT, 5 nm away ## 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 20190713011389A](https://openairdocs.org/incident/20190713011389A), Jul 13, 2019: Bell 47G-3B-1, Mosby, MT, Destroyed. Pilot was landing at a private ranch with two passengers and was unable to maintain directional control upon landing. Witness stated the rotorcraft started… ## Other investigations on N3078G (2) 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. - [NTSB ATL94LA014](https://openairdocs.org/ntsb/ATL94LA014), Nov 12, 1993: Bell 47G-3B-1 Soloy (N3078G), Atmore, AL, substantial damage. Probable cause: THE PILOT'S INADEQUATE PRE-FLIGHT INSPECTION. FACTORS WERE THE LACK OF A FILTER ON THE REFUELING PUMP WHICH WOULD PRECLUDE WATER PASSAGE, AND THE HIGH TREES. - [NTSB SEA79FTI19](https://openairdocs.org/ntsb/SEA79FTI19), Jun 25, 1979: Bell 47G3B1 (N3078G), Emigrant, MT, substantial damage ## Docket (10 files) The files NTSB released with the investigation on March 17, 2022, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=99890. 13.4 MB in all. - Pilot/operator aircraft accident report, NTSB form 6120.1 (item 1, PDF, 9 pages, 1.8 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=9666926&FileExtension=pdf&FileName=NTSB%20accident%20report%206120_1_Redacted-Rel.pdf - Pilot's statement (item 2, PDF, 2 pages, 147 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=12365766&FileExtension=pdf&FileName=Pilot%27s%20Statement-Rel.pdf - Passenger interviews (item 3, PDF, 2 pages, 124 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13366397&FileExtension=pdf&FileName=Passenger%20Interviews-Rel.pdf - Operator and witness interviews (item 4, PDF, 6 pages, 299 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13367346&FileExtension=pdf&FileName=Interviews-Rel.pdf - Airframe and engine exam report (item 5, PDF, 10 pages, 2.5 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13372450&FileExtension=pdf&FileName=Airframe%20and%20Engine%20Examination%20WPR19LA194-Rel.pdf - Performance planning card / load calculation (item 6, PDF, 1 page, 3.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=9664970&FileExtension=pdf&FileName=load%20calculation-Rel.pdf - Pilot's training record (item 7, PDF, 4 pages, 1.1 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=12373959&FileExtension=pdf&FileName=Pilot%20Training%20record_Redacted-Rel.pdf - Statement of party representatives to NTSB investigation (item 8, PDF, 1 page, 112 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13381178&FileExtension=pdf&FileName=PARTY%20REPRESENTATIVE%20WPR19LA194_Redacted-Rel.pdf - Release of aircraft wreckage, NTSB form 6120.15 (item 9, PDF, 1 page, 848 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=9668075&FileExtension=pdf&FileName=Wreckage%20Release%20Form_Redacted-Rel.pdf - Photo array (item 10, PDF, 7 pages, 3.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=12366068&FileExtension=pdf&FileName=Photos%20WPR19LA194-Rel.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.