# NTSB WPR22LA221: Bell 206B, N90326, Stockton, CA, June 17, 2022 - Type: NTSB accident investigation - Classification: Accident · No injuries · Class 3 · Limited · Final report - Date: June 17, 2022, 06:15 local (13:15 UTC) - Place: Stockton, CA - Coordinates: 37.908851, -121.37392 - Nearby events: https://openairdocs.org/map.md?lat=37.9089&lon=-121.3739&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Defining event: [Enroute: Unknown or undetermined](https://openairdocs.org/ntsb-events/000) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Western Pacific Region - Parties: Van Horn Aviation, Federal Aviation Administraion - NTSB case key (mKey): 105297 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR22LA221 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/105297/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=105297 - Page: https://openairdocs.org/ntsb/WPR22LA221 ## Probable cause Tail rotor blade impact with an unidentified object, which resulted in the loss of control and subsequent rollover of the helicopter. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Tail rotor: tail rotor blade](https://openairdocs.org/ntsb-findings/01046410): Aircraft › Aircraft propeller/rotor · Damaged/degraded (probable cause); cases with it: [Bell 206B, 2 cases](https://openairdocs.org/ntsb-findings/01046410/cases.md?model=1181511), [All aircraft, 31 cases](https://openairdocs.org/ntsb-findings/01046410/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Enroute: Unknown or undetermined](https://openairdocs.org/ntsb-events/000) (defining event); cases with it: [Bell 206B, 5 cases](https://openairdocs.org/ntsb-events/000/sequence.md?model=1181511), [All aircraft, 1,703 cases](https://openairdocs.org/ntsb-events/000/sequence.md) - [Landing: Attempted remediation/recovery](https://openairdocs.org/ntsb-events/060); cases with it: [Bell 206B, 14 cases](https://openairdocs.org/ntsb-events/060/sequence.md?model=1181511), [All aircraft, 1,422 cases](https://openairdocs.org/ntsb-events/060/sequence.md) - [Landing: Loss of control in flight](https://openairdocs.org/ntsb-events/240); cases with it: [Bell 206B, 32 cases](https://openairdocs.org/ntsb-events/240/sequence.md?model=1181511), [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 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 The pilot had departed his home base to relocate the helicopter for an upcoming aerial application job when he felt a vibration and heard a bang, followed immediately by an uncommanded right yaw. While performing a precautionary landing to an orchard, the helicopter entered an uncommanded, continuous right rotation about the vertical axis. The pilot rolled off the throttle and increased collective to cushion the landing, but the helicopter continued the right rotation as it touched down, which resulted in the helicopter rolling over onto its left side. The helicopter sustained substantial damage to the fuselage, transmission, main rotor, and tail rotor assemblies. Fragments of one tail rotor blade was recovered about 2,000 ft from the main wreckage. The pilot stated that he was unsure if a bird had struck the tail rotor during flight. Postaccident examination of the tail rotor assembly revealed both blades were damaged, and one blade fractured and separated from the hub. The tail rotor blades were shipped to the National Transportation Safety Board (NTSB) materials laboratory, and subsequently to the manufacturer’s laboratory for further examination. The combined examinations revealed translaminar overstress fractures of both tail rotor blades, with one blade exhibiting a leading-edge high-energy impact. Both blades exhibited an unidentified foreign material transfer onto their leading edges. A small amount of nitrile rubber was found lodged into the end of one blade; however, its origin was undetermined. ## Factual narrative On June 21, 2022, about 06015 Pacific daylight time, a Bell 206B helicopter, N90326, was substantially damaged when it was involved in an accident near Stockton, California. The pilot was not injured. The helicopter was operated as a Title 14 Code of Federal Regulations Part 91 ferry flight. According to the pilot, he was enroute to a field, but was carrying no chemicals. He was about 12 minutes into the flight when he felt a vibration that lasted no more than 10 seconds. He then heard a bang followed by a sharp right yaw. He lowered the collective and rolled the throttle down to bring the helicopter back into controlled forward flight. He maneuvered the helicopter for about a half mile to a “young orchard,” and planned to do a run-on landing between the small trees. When the helicopter had slowed to about 25 mph, and while about 20 ft above ground level (agl), it began an uncommanded rotation to the right. The pilot then rolled off the throttle and tried to cushion the landing. The helicopter landed level but continued to rotate, which resulted in it rolling onto its left side, substantially damaging the fuselage, main rotor, and tail rotor assemblies. Before the pilot exited the helicopter through the co-pilot's windshield, he shut down the engine and turned the fuel switch off. The pilot stated that he did not know if he had hit a bird. The postaccident examination, conducted by the Federal Aviation Administration (FAA), revealed structural damage to the fuselage, the transmission mount, and the main rotor and tail rotor assemblies. The tail rotor gearbox (gearbox) had separated from the end of the tailboom at the four mounting bolts, and the gearbox mounting shims were found scattered on the ground about 10 ft behind the tail rotor mount. The tail rotor control bellcrank rod end was sheared off near the gearbox. One tail rotor blade remained wholly attached on the hub but was damaged. The other tail rotor blade fractured and separated from the hub and about 80% of the blade was missing. The root end of the blade remained installed on the hub. The missing two sections of the blade were found about 2,000 ft north of the main wreckage. The tail rotor assembly, along with the gearbox and its mounting hardware, were shipped to the NTSB materials laboratory for further examination. The metallurgical examination revealed that the pitch change control rod and the four gearbox mounting bolts had overstress fractures. The blade grips, hub, and pitch change links revealed no witness marks or indications of preexisting damage. The tail rotor blades were examined by the NTSB, and subsequently, by Van Horn Aviation, LLC, the blade manufacturer. The blades were FAA PMA (Parts Manufacturer Approval) components. The two blades, serial number C548, and C549 are shown in Figures 1 and 2. Figure 1. Tail rotor blade C548. Figure 2. Tail rotor blade C549. Blade C548 had partially separated along the centerline, exhibiting a loss of outboard skin, shown near theblack stripe. The fracture on blade C548 exhibited a zig-zag pattern, oriented 45° in some locations and parallel with the blade direction in others. These orientations were consistent with fracture along the fiber direction of the composite, across different plies, which were oriented in different directions. The fiber composite also exhibited irregular and erratic fracture patterns, consistent with overstress fracture across multiple plies (translaminar). Blade C549 had wholly fractured and exhibited three major remnants. The blade fractured along the root of the blade, with the outboard portion cracking along the interior foam core. Only the base of the blade remained installed on the tail rotor hub. Like with the other tail rotor blade, fracture directions were consistent with the fiber direction of the ply when located along the composite layup of the blade. Unlike the other tail rotor blade, this blade was absent the tip, with the outboard 2.5 inches of material missing. This blade also exhibited features that were consistent with a translaminar fracture of the composite, as opposed to an interlaminar delamination fracture. According to the manufacturer, in the fractured tip area the abrasion strip exhibited denting, folding, and debonding/delamination along the aft edge as well as discoloration from a foreign material. The extensive deformation of the abrasion strip was consistent with a high energy impact on the leading edge. The manufacturer identified multiple scrapes and material transfer onto blade C548, as shown in figure 3, and discoloration from foreign materials on blade C549, as shown in figure 4. A small amount of foreign matter, identified as nitrile rubber, was found lodged in the fractured blade end. Figure 3. Blade C548, exhibiting scrapes and material transfer on the leading edge. Figure 4. Mosaic of photos of Blade 549, exhibiting discoloration and a small amount of foreign matter lodged in the blade end. ## Aircraft - Registration: [N90326](https://openairdocs.org/deregistered/N90326-2024-12-28), registration cancelled 2024-12-28, S/N 1764, built 1975 (OpenAirDocs) - Reported make and model: BELL 206B - Registry model: [Bell 206B](https://openairdocs.org/model/bell-206b) (registry code 1181511) (OpenAirDocs) - Registry engine: [Allison 250 SER 400HP](https://openairdocs.org/engine/allison-250-ser-400hp) (registry code 03013, turbo-shaft) (OpenAirDocs) - Category: Helicopter - Serial number: 1764 - Year built: 1975 - Engines: Rolls-Royce 250-C20B 420 horsepower turbo shaft - Damage: Substantial damage - Flight: Positioning, Part 91 - Operator: Alpine Helicopter Service Inc - Registered owner: Alpine Helicopter Service Inc - Airworthiness certificate: Standard, Normal; Special, Restricted (Special) - Departed: Lodi, CA - Destination: Same as departure - Airport: NA - Equipment: ADS-B ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 72; injuries: none; commercial, private; airplane ratings: single-engine sea; instrument ratings: airplane; medical: class 2, with waivers/limitations; last flight review March 5, 2022; seat: right; restraint: lap only; flight hours: 31,697 total, 14,406 in this make and model, 31,399 as pilot in command, 75 in the last 90 days, 27 in the last 30 days ## Weather - Conditions: Visual (VMC), Day - Wind: 260° at 9 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 57 °F, dew point 45 °F - Altimeter: 29.86 inHg - Observed at: KSCK, 7 nm away - METAR: KSCK 171255Z AUTO 26009KT 10SM CLR 14/07 A2986 RMK AO2 SLP110 T01390072 $ ## 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 20220617006419A](https://openairdocs.org/incident/20220617006419A), Jun 17, 2022: Bell 206B, Stockton, CA, Destroyed. Agricultural helo (no chemicals) crashed. Summary of findings: Helicopter resting on l/h side in almond tree orchard. Helicopter is intact other than a missing… ## Docket (7 files) The files NTSB released with the investigation on April 18, 2024, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=105297. 18.6 MB in all. - Pilot/operator aircraft accident report, NTSB form 6120.1 (item 1, PDF, 9 pages, 5.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=15386306&FileExtension=pdf&FileName=Acciden.Incident%20Report%20NTSB%20-%20June%2017.2022_Redacted-Rel.pdf - Photos (item 2, PDF, 4 pages, 2.9 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=15386705&FileExtension=pdf&FileName=Photos%20for%20WPR22LA221-Rel.pdf - Pilot's statement (item 3, PDF, 3 pages, 104 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=15587508&FileExtension=pdf&FileName=Interviews%20with%20Pilot-Rel.pdf - Materials laboratory factual report (item 4, PDF, 30 pages, 35 photos, 6.4 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=15816370&FileExtension=pdf&FileName=23-052%20-%20Materials%20Lab%20Factual%20Report%20(WPR22LA221)-Rel.pdf - Materials laboratory addendum report (item 5, PDF, 7 pages, 6 photos, 977 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=15996305&FileExtension=pdf&FileName=23-052B%20-%20Materials%20Lab%20Addendum%20Report%20(WPR22LA221)-Rel.pdf - FAA field examination of accident scene (item 6, PDF, 2 pages, 79 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16051460&FileExtension=pdf&FileName=FAA%20N90326%20Accident%20Report%20WPR22LA221%20%206-14-2022-Rel.pdf - Manufacturer's examination report (item 7, PDF, 28 pages, 2.8 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16451939&FileExtension=pdf&FileName=206BT-STR-508%20N90326%20Crash%20Damage%20Evaluation%20Report,%20Rev%20NC_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.