# NTSB ERA24LA076: Bell Helicopter Textron 206L-1, N571CJ, Walland, TN, December 28, 2023 - Type: NTSB accident investigation - Classification: Accident · No injuries · Class 3 · Limited · Final report - Date: December 28, 2023, 13:40 local (18:40 UTC) - Place: Walland, TN · 4291 Old Walland Hwy, Walland, TN - Coordinates: 35.764226, -83.849319 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=35.7642&lon=-83.8493&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Defining event: [Enroute: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) - Highest injury: No injuries - Injuries: 6 uninjured - Status: Completed, report March 18, 2026 - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Eastern Region Aviation - Parties: Transportation Safety Board of Canada, Rolls-Royce Corporation, FAA/FSDO - NTSB case key (mKey): 193577 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ERA24LA076 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/193577/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=193577 - Page: https://openairdocs.org/ntsb/ERA24LA076 ## Probable cause The improper installation of the No. 8 bearing spanner nut, which resulted in the No. 8 bearing’s failure, and the subsequent total loss of engine power. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Maintenance: installation](https://openairdocs.org/ntsb-findings/02062035): Personnel issues › Task performance · Maintenance personnel (probable cause); cases with it: [Bell Helicopter Textron 206L-1, 2 cases](https://openairdocs.org/ntsb-findings/02062035/cases.md?model=1182107), [All aircraft, 371 cases](https://openairdocs.org/ntsb-findings/02062035/cases.md) - [Engine (turbine/turboprop): turbine section](https://openairdocs.org/ntsb-findings/01057250): Aircraft › Aircraft power plant · Incorrect service/maintenance (probable cause); cases with it: [Bell Helicopter Textron 206L-1, 3 cases](https://openairdocs.org/ntsb-findings/01057250/cases.md?model=1182107), [All aircraft, 74 cases](https://openairdocs.org/ntsb-findings/01057250/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Enroute: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) (defining event); cases with it: [Bell Helicopter Textron 206L-1, 7 cases](https://openairdocs.org/ntsb-events/341/sequence.md?model=1182107), [All aircraft, 3,820 cases](https://openairdocs.org/ntsb-events/341/sequence.md) - [Emergency descent: Off-field or emergency landing](https://openairdocs.org/ntsb-events/440); cases with it: [Bell Helicopter Textron 206L-1, 6 cases](https://openairdocs.org/ntsb-events/440/sequence.md?model=1182107), [All aircraft, 3,365 cases](https://openairdocs.org/ntsb-events/440/sequence.md) ## Analysis About 35 minutes into the local sightseeing tour flight the pilot observed the engine chip light illuminate on the instrument panel. The pilot immediately began maneuvering toward a landing area and, within a few seconds, he heard an abnormal noise from the engine and saw the engine’s oil temperature and pressure indications decrease to zero. The pilot entered an autorotation and, shortly after, the engine stopped producing power. During the autorotation landing to a field, the helicopter touched down hard, skidded forward, and the main rotor blades contacted one of the vertical stabilizers, nearly severing the tailboom. Subsequent examination of the helicopter’s engine revealed that no locking crimp had been made on the No. 8 bearing spanner nut during the last assembly, which allowed the nut to lose its torque, ultimately resulting in thermal damage and disintegration of the No. 8 bearing. This resulted in the compressor turbine shaft losing its retention and concentric location. The No. 8 bearing spanner nut had a partial crimp that exhibited a tool pry mark consistent with its removal during the last disassembly; however, it had not been blended away, nor had a new crimp been applied, consistent with the procedures described by the engine manufacturer’s overhaul manual. Additionally, the inside of the bearing’s sump cover showed rotational scoring consistent with contact with the No. 8 bearing spanner nut during engine operation, and rub damage on the power turbine support and 2nd stage turbine wheel, which was indicative of a loss of axial and radial retention of the gas producer rotor. This condition ultimately resulted in the total loss of engine power. ## Factual narrative On December 28, 2023, about 1340 eastern standard time, a Bell 206L-1 helicopter, N571CJ, was substantially damaged when it was involved in an accident near Walland, Tennessee. The pilot and five passengers were not injured. The helicopter was operated by Whirl'd Helicopters, Inc. (doing business as Scenic Helicopter Tours) as a Title 14 Code of Federal Regulations Part 91 revenue sightseeing flight. The flight departed from Eagles Landing Heliport (03TN), Sevierville, Tennessee, about 1300 for a local tour flight. About 35 minutes into the flight, the pilot observed an engine chip light announcement on the instrument panel. The pilot immediately began maneuvering toward a landing area and, within a few seconds, he heard an abnormal noise from the engine and saw the engine oil temperature and pressure indications decrease to zero. The pilot immediately entered an autorotation while continuing to maneuver to the landing area. About 3 to 5 seconds later, the engine stopped producing power. During the autorotation landing to a field, the helicopter touched down hard, skidded forward several feet, and came to a stop. During this time, the main rotor blades contacted one of the vertical stabilizers, nearly severing the tailboom. The engine was a Rolls-Royce 250-C28B and had accumulated 13,378.7 hours time since new (TSN). The engine was last repaired on July 27, 2021. The gearbox assembly was installed on July 14, 2021, and the compressor assembly was installed on July 27, 2021, at an engine TSN of 12,823.3 hours. The turbine assembly was installed on July 24, 2019, at an engine TSN of 11,980.9 hours. A postaccident field examination revealed that all the 4th stage turbine blades were intact, but most of the blade shrouds were worn away. Manual rotation of the N1 rotor spool resulted in rotation of the N2 rotor spool, consistent with a mechanical lock between shafts. The upper chip detector showed a coating of black paste and metallic debris, and the lower chip detector was clean of ferrous debris. The engine to airframe oil tank lines were found secure with no evidence of leakage. Residual oil was observed in the supply line from the oil tank to the engine, the return line was void of oil, and the engine oil tank contained less than half a tank of oil. About 16 ounces of oil was drained from the accessory gear box. Engine disassembly revealed that the compressor module was intact and undamaged, and the compressor impeller turned freely and smoothly. The spur adapter gearshaft (SAG) was intact and undamaged, and the turbine-to-compressor coupling spline was intact. The aft SAG O-ring was disintegrated into coarse black paste, and there was no evidence of an O-ring in the forward SAG O-ring groove. The accessory gearbox internal components and oil scavenge and pressure pumps were undamaged and well lubricated. The 4th stage turbine wheel was intact, but the curvic coupling mating it with the 3rd stage turbine wheel showed rotational smearing. Further,most of the blade shrouds were rotationally abraded away, consistent with contact against the 4th stage wheel tracks. The 4th stage turbine nozzle was intact but showed rotational scoring on the 3rd and 4th stage turbine wheel tracks. The power turbine bearing support was intact, but the 3rd and 1st stage turbine wheels could not be withdrawn because the turbine-to-compressor coupling and the power turbine inner shaft were fractured and deformed outward, which locked the 3rd stage turbine wheel. The 3rd stage turbine wheel was intact, but the curvic coupling mating with the 4th stage turbine wheel showed rotational smearing. All 3rd stage turbine wheel blades were intact. The combustor outer case and the combustor liner were intact and undamaged, and the fuel nozzle was intact, undamaged, and clean. The No. 8 bearing sump cavity was found dry and coated with a black residue, and the No. 8 bearing spanner nut was found untorqued and backed out until about the last thread. The No. 8 bearing spanner nut exhibited one partial crimp and two blended locations. Generally, when a No. 8 bearing spanner nut is removed during overhaul, the previous locking crimp must first pried open before the nut can be unscrewed. The overhaul manual allows each crimp to be used only once, so the previous deformed crimped material on the nut must be blended away and a new crimp location must be chosen on the nut after it is re-torqued onto the shaft during re-assembly of the engine. Examination of the partial crimp that was found on the No. 8 bearing spanner nut, revealed a pry mark on the inner surface of the crimp ring, which was consistent with the removal of the crimp during the last disassembly. Additionally, the inner crimp surface was oxidized, due to exposure to the hot gases during engine operation, consistent with a non-contact condition the turbine wheel shaft. No evidence was found that locking crimp was made on the No. 8 bearing spanner nut during the last assembly. The No. 8 bearing sump cover showed rotational scoring consistent with contact with the No. 8 bearing spanner nut during engine operation. The No. 8 bearing exhibited significant wear and thermal damage to the bearing balls and inner ring, as well as a loss of the forward shoulder of the inner raceway ring. Rub damage on the power turbine support and 2nd stage turbine wheel was consistent with loss of axial and radial retention of the gas producer rotor during operation. ## Aircraft - Registration: [N571CJ](https://openairdocs.org/aircraft/N571CJ), registered now, S/N 45781, built 1983 (OpenAirDocs) - Reported make and model: BELL HELICOPTER TEXTRON 206L-1 - Registry model: [Bell Helicopter Textron 206L-1](https://openairdocs.org/model/bell-helicopter-textron-206l-1) (registry code 1182107) (OpenAirDocs) - Registry engine: [Allison 250-C28 series](https://openairdocs.org/engine/allison-250-c28-series) (registry code 03022, turbo-shaft) (OpenAirDocs) - Category: Helicopter - Serial number: 45781 - Year built: 1983 - Airframe hours: 24059.2 - Engines: Rolls Royce RR 250 C28-B 420 horsepower turbo jet - Damage: Substantial damage - Flight: Aerial observation, Part 91 - Operator: Whirl'd Helicopters Inc, doing business as Scenic Helicopter Tours - Registered owner: Rotorpro LLC - Airworthiness certificate: Standard, Normal - Last inspection: Continuous airworthiness, December 26, 2023, 57.5 hours before - Departed: 03TN, Sevierville, TN - Airport: NONE - Equipment: Stall warning system, Onboard weather, Handheld GPS, ADS-B ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 38; injuries: none; flight instructor, commercial; instrument ratings: helicopter; medical: class 2, without waivers/limitations; last flight review April 11, 2023; seat: front; restraint: 4-point; flight hours: 2,785 total, 880 in this make and model, 2,730 as pilot in command, 145 in the last 90 days, 25 in the last 30 days, 1 in the last 24 hours - Pilot-rated passenger; injuries: none; seat: left; restraint: lap only ## Weather - Conditions: Visual (VMC), Day - Wind: 240° at 11 knots - Visibility: 10 statute miles - Temperature: 46 °F, dew point 34 °F - Altimeter: 29.82 inHg - Observed at: TYS, 7 nm away - METAR: KTYS 281853Z 24011KT 10SM SCT034 08/01 A2982 RMK AO2 SLP097 T00830006 ## 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 20231228019719A](https://openairdocs.org/incident/20231228019719A), Dec 28, 2023: Bell Helicopter Textron 206L-1, Walland, TN, Substantial damage. During sight seeing tour flight, pilot observed an illuminated eng chip light. During monovering for landing, pilot heard abnormal noise and observed engine… ## Docket (7 files) The files NTSB released with the investigation on March 18, 2026, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=193577. 10.0 MB in all. - Pilot/operator aircraft accident report, NTSB form 6120.1 (item 1, PDF, 11 pages, 2.1 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19629833&FileExtension=pdf&FileName=6120%20Accident%20Report_Signed_Redacted-Rel.pdf - Record of conversation_pilot (item 2, PDF, 2 pages, 101 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19629524&FileExtension=pdf&FileName=ERA24LA076%20MOR%20Pilot_Redacted-Rel.pdf - Powerplants factual report (item 3, PDF, 23 pages, 30 photos, 4.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=18979795&FileExtension=pdf&FileName=ERA24LA076-pp-factual-Rel.pdf - NTSB examination report (item 4, PDF, 8 pages, 994 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19628606&FileExtension=pdf&FileName=ERA24LA076%20Engine%20Examination-Rel.pdf - Photos_accident site and damage (item 5, PDF, 3 pages, 544 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19632503&FileExtension=pdf&FileName=Photo%20Array_Accident%20Site%20and%20Damage-Rel.pdf - Wreckage retention and release_signed (item 6, PDF, 1 page, 710 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19637017&FileExtension=pdf&FileName=Whirl%27d%20NTSB%20Wreckage%20Release%20Parts%20Receipt%20Signed_Redacted-Rel.pdf - Certification of party representative to an NTSB investigation (item 7, PDF, 14 pages, 1.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19643327&FileExtension=pdf&FileName=NTSB%20Party%20Guidance%20and%20Form%20Rolls%20Royce_Redacted-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.