# NTSB WPR19LA122: Bell 206, N206JH, Oakridge, OR, April 26, 2019 - Type: NTSB accident investigation - Classification: Accident · No injuries · Class 3 · Limited · Final report - Date: April 26, 2019, 07:00 local (14:00 UTC) - Place: Oakridge, OR - Coordinates: 43.55389, -122.47583 - Nearby events: https://openairdocs.org/map.md?lat=43.5539&lon=-122.4758&mi=10 - Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping) - Defining event: [Maneuvering-low-alt flying: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Western Pacific Region - Parties: Rolls Royce, Federal Aviation Administration FSDO - NTSB case key (mKey): 99326 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR19LA122 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/99326/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=99326 - Page: https://openairdocs.org/ntsb/WPR19LA122 ## Probable cause A total loss of engine power following the failure of a 3rd stage turbine blade due to low- and high-cycle fatigue. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Engine (turbine/turboprop): turbine section](https://openairdocs.org/ntsb-findings/01057250): Aircraft › Aircraft power plant · Failure (probable cause); cases with it: [Bell 206B, 2 cases](https://openairdocs.org/ntsb-findings/01057250/cases.md?model=1181511), [All aircraft, 74 cases](https://openairdocs.org/ntsb-findings/01057250/cases.md) - [Engine (turbine/turboprop): turbine section](https://openairdocs.org/ntsb-findings/01057250): Aircraft › Aircraft power plant · Fatigue/wear/corrosion (probable cause); cases with it: [Bell 206B, 2 cases](https://openairdocs.org/ntsb-findings/01057250/cases.md?model=1181511), [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. - [Maneuvering-low-alt flying: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) (defining event); cases with it: [Bell 206B, 17 cases](https://openairdocs.org/ntsb-events/341/sequence.md?model=1181511), [All aircraft, 3,820 cases](https://openairdocs.org/ntsb-events/341/sequence.md) - [Emergency descent: Collision with terr/obj (non-CFIT) ](https://openairdocs.org/ntsb-events/470); cases with it: [Bell 206B, 57 cases](https://openairdocs.org/ntsb-events/470/sequence.md?model=1181511), [All aircraft, 10,189 cases](https://openairdocs.org/ntsb-events/470/sequence.md) ## Analysis During the agricultural aerial application flight, the helicopter lost engine power, and the pilot performed an autorotation into sloping, tree-covered terrain. Examination of the engine revealed that a blade from the 3rd stage turbine wheel had been liberated, resulting in the loss of engine power. The blade’s fracture surface indicated that it was initiated in a low-cycle fatigue mode near the trailing edge radius of the blade and progressed to a high-cycle fatigue process along the blade chord, which finally resulted in overload failure. The initiation event for the failure could not be determined; however, it was likely caused by operation within an engine speed avoidance range, an engine speed/airframe interaction of unknown origin, inadequate engine temperature management on startup, inadequate wheel design or undetermined manufacturing defect, or combinations thereof. The blade had not been operated beyond its overhaul or inspection time limit. Similar blade failure was associated with five previous accidents and two previous incidents. An in-service replacement program was started by the engine manufacturer on July 30, 2021, requiring removal and replacement of the 3rd stage turbine wheel with a new design at the next scheduled replacement time. ## Factual narrative On April 26, 2019, about 0700 Pacific daylight time, a Bell 206B, N206JH, was substantially damaged when it was involved in an accident near Oakridge, Oregon. The pilot was not injured. The helicopter was operated as a Title 14 Code of Federal Regulations Part 137 aerial application flight. The pilot had just sprayed a load of herbicide on trees and was maneuvering the helicopter for a final pass to complete the dispersal when he heard a faint buzzing sound that lasted about 1 to 2 seconds. There were no accompanying annunciator light warnings, and he did not hear any alert horns, but noticed that the engine power turbine (N2) gauge was oscillating about the 11 to 12 o'clock position (50-65% range). The rotor tachometer speed remained within the operating range, and he decided to perform an autorotation. The helicopter landed on sloping, tree-covered terrain and rolled over. The helicopter was equipped with a Rolls Royce M250-C20B turbo-shaft engine. Initial external inspection indicated that the N2 stage had locked, and that the exhaust duct and stacks exhibited multiple dents to their inner surfaces expanding in an outward direction. Disassembly and examination revealed that one blade of the 3rd stage turbine wheel, immediately following a shroud slot, was fractured and had liberated near the inner platform at the blade root. Visual examination of the fracture surface revealed progressive growth ring signatures consistent with fatigue from the trailing edge to approximately 2/3 along the chord, at which point the fracture surface changed texture, becoming rough, consistent with overload failure. The 3rd stage turbine wheel was sent to the Rolls Royce materials laboratory for further assessment. Evaluation revealed that the fracture initiated in a low-cycle fatigue near the trailing edge radius of the blade and progressed to a high-cycle fatigue process along the blade chord, which resulted in overload failure. Fluorescent penetrant inspection further revealed that the trailing edges of all airfoils within the packet that contained the failed blade, along with the preceding blade, exhibited cracks at similar locations on the blade root radius. Furthermore, the pressure side wax weld adjacent to every airfoil appeared to intersect the airfoil root radius. The wheel was identified as part of a post-service bulletin (SB) commercial engine bulletin (CEB)-1365 or “enhanced” turbine assembly design released by Rolls Royce in November 1999. The life limit for the wheel was 4,550 hours, and 6,000 cycles. The recommended time between overhaul for the turbine module was 3,500 hours. Maintenance records indicated that the accident 3rd stage wheel had accumulated 1,661.9 hours in 1,030 cycles. SB CEB-A-1400, Steady State Operation Avoidance Range Limit, was originally released in December 2006 and revised six times through January 2019. The SB was intended to reduce the possibility of high cycle fatigue in the 3rd stage turbine wheel by providing a seriesof speed avoidance restrictions. According to Rolls Royce records, the wheel released as part of SB CEB-1365 had been associated with five previous accidents and two previous incidents. As part of a mitigation plan, Rolls Royce undertook a redesign of the 3rd stage turbine wheel, featuring a modified fillet radius at the platform and improved manufacturing processes to reduce fillet variations, with production that began in December 2020. An in-service replacement program was begun on July 30, 2021, via SB CEB A-1428, requiring removal of the SB CEB-1365 3rd stage turbine wheel and installation of the new SB CEB A-1428 3rd stage turbine wheel no later than the next gas producer turbine wheel replacement time. An FAA Airworthiness Directive (AD) was planned to mandate the incorporation of SB CEB A-1428; however, as of the time of publication of this report, the release of the AD has not yet been established. ## Aircraft - Registration: [N206JH](https://openairdocs.org/deregistered/N206JH-2019-11-29), registration cancelled 2019-11-29, S/N 2918, built 1980 (OpenAirDocs) - Reported make and model: Bell 206 (B) - Registry model: [Bell 206B](https://openairdocs.org/model/bell-206b) (registry code 1181511) (OpenAirDocs) - Registry engine: [Rolls-Royce 250-C20B](https://openairdocs.org/engine/rolls-royce-250-c20b) (registry code 54385, turbo-shaft) (OpenAirDocs) - Category: Helicopter - Serial number: 2918 - Year built: 1980 - Airframe hours: 12816.4 - Engines: Rolls Royce M250-C20B 420 horsepower turbo shaft - Damage: Substantial damage - Flight: Aerial application, Part 137 - Operator: Wilbur Ellis Co - Registered owner: Wilbur Ellis Co - Airworthiness certificate: Special, Restricted (Special) - Last inspection: Annual, April 17, 2019, 27.5 hours before - Departed: Oakridge, OR - Destination: Oakridge, OR - Equipment: Satellite tracking device ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 35; injuries: none; commercial; airplane ratings: single-engine land; instrument ratings: airplane; medical: class 2, without waivers/limitations; last flight review May 20, 2017; seat: right; restraint: 4-point; flight hours: 615 total, 370 in this make and model, 570 as pilot in command, 56 in the last 90 days, 47 in the last 30 days ## Weather - Conditions: Visual (VMC), Day - Wind: calm - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 48 °F, dew point 37 °F - Altimeter: 30.20 inHg - Observed at: KRBG, 43 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 20190426016859A](https://openairdocs.org/incident/20190426016859A), Apr 26, 2019: Bell 206B, Oakridge, OR, Substantial damage. On April 26th, 2019 N206JH, a Bell 206B3, crashed while conducting an agricultural spray operation in clearwater, OR. The aircraft was being operated under CFR… ## Other investigations on N206JH (1) 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 LAX84LA117](https://openairdocs.org/ntsb/LAX84LA117), Dec 27, 1983: Bell 206B III (N206JH), Mountain City, NV, substantial damage ## Docket (6 files) The files NTSB released with the investigation on April 19, 2022, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=99326. 18.4 MB in all. - Powerplants chairman's factual report (item 1, PDF, 26 pages, 26 photos, 3.7 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13200417&FileExtension=pdf&FileName=WPR19LA122-pp-fact-Rel.pdf - Powerplants - rolls royce lab report (item 2, PDF, 64 pages, 13.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13624236&FileExtension=pdf&FileName=19FAE-061-PR-Rel.pdf - Pilot/operator aircraft accident report, NTSB form 6120.1 (item 3, PDF, 11 pages, 543 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13688762&FileExtension=pdf&FileName=122%206120_1_Redacted-Rel.pdf - Maintenance logbook excerpts (item 4, PDF, 3 pages, 263 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13394983&FileExtension=pdf&FileName=r_Logbook%20Excerpts_Redacted-Rel.pdf - Statement of party representatives to NTSB investigation (item 5, PDF, 10 pages, 94 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13381144&FileExtension=pdf&FileName=r_Party%20RR%20a_Redacted-Rel.pdf - Release of aircraft wreckage, NTSB form 6120.15 (item 6, PDF, 1 page, 534 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13623454&FileExtension=pdf&FileName=Release%20of%20Wreckage_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.