# NTSB WPR21LA354: Hiller UH-12E, N5334V, Bovill, ID, September 23, 2021 - Type: NTSB accident investigation - Classification: Accident · No injuries · Class 3 · Limited · Final report - Date: September 23, 2021, 15:00 local (22:00 UTC) - Place: Bovill, ID - Coordinates: 46.840453, -116.2866 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=46.8405&lon=-116.2866&mi=10 - Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping) - Defining event: [Maneuvering-hover: 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: Rolls Royce, FAA-Spokane - NTSB case key (mKey): 103976 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR21LA354 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/103976/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=103976 - Page: https://openairdocs.org/ntsb/WPR21LA354 ## Probable cause A loss of helicopter control for undetermined reasons based on the available evidence for this accident. ## 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: [Hiller UH-12E, 7 cases](https://openairdocs.org/ntsb-findings/02063040/cases.md?model=4360122), [All aircraft, 9,295 cases](https://openairdocs.org/ntsb-findings/02063040/cases.md) - [Not determined](https://openairdocs.org/ntsb-findings/05000000): Not determined › Not determined · Unknown/Not determined (probable cause); cases with it: [Hiller UH-12E, 5 cases](https://openairdocs.org/ntsb-findings/05000000/cases.md?model=4360122), [All aircraft, 2,247 cases](https://openairdocs.org/ntsb-findings/05000000/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Maneuvering-hover: Unknown or undetermined](https://openairdocs.org/ntsb-events/000) (defining event); cases with it: [Hiller UH-12E, 3 cases](https://openairdocs.org/ntsb-events/000/sequence.md?model=4360122), [All aircraft, 1,703 cases](https://openairdocs.org/ntsb-events/000/sequence.md) - [Maneuvering-hover: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342); cases with it: [Hiller UH-12E, 3 cases](https://openairdocs.org/ntsb-events/342/sequence.md?model=4360122), [All aircraft, 1,858 cases](https://openairdocs.org/ntsb-events/342/sequence.md) - [Maneuvering-hover: Loss of control in flight](https://openairdocs.org/ntsb-events/240); cases with it: [Hiller UH-12E, 7 cases](https://openairdocs.org/ntsb-events/240/sequence.md?model=4360122), [All aircraft, 5,002 cases](https://openairdocs.org/ntsb-events/240/sequence.md) ## Analysis The helicopter was performing an aerial application flight. While approaching the fertilizer service truck to refill the bucket, the pilot felt a “sudden jolt,” and the helicopter lost altitude. The pilot was unable to regain control, and the helicopter did not yaw after the jolt. The helicopter subsequently impacted the terrain below. The helicopter sustained substantial damage to its main rotor blades and fuselage. Before the pilot could exit the helicopter, “everything” on the helicopter, including the engine, automatically shut down. Postaccident examination of the wreckage, including the engine, revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation. Also, the examination yielded no evidence to explain why the engine automatically shut down after the accident. As a result, the reason for the pilot’s loss of helicopter control could not be determined based on the available evidence for this accident investigation. ## Factual narrative On September 23, 2021, about 1500 Pacific daylight time, a Hiller UH-12E helicopter, N5334V, was substantially damaged when it was involved in an accident near Bovill, Idaho. The pilot was not injured. The helicopter was operated as a Title 14 Code of Federal Regulations Part 137 aerial application flight. The pilot reported that he had been applying dry fertilizer over trees as part of a timber company contract and had flown about 5.7 hours that day. The pilot also reported that he refueled the helicopter every hour. About 20 minutes after the last refueling, the pilot was on approach to the fertilizer service truck to refill the bucket. About 40 ft above ground level and about 20 ft from the truck, the pilot felt a “sudden jolt,” and the helicopter “dropped” to the sloping terrain below. The pilot stated that he had no time to react and that the helicopter did not yaw after the jolt. He recalled that the torque gauge indicated between 85% and 90% at the time. The helicopter impacted the ground and came to rest on its side. The pilot further stated that “everything” on the helicopter automatically shut down before he exited. A witness, who was staffing the truck, stated that he did not hear anything abnormal regarding the engine. The witness also stated that the wind was light and variable at the time of the accident. Review of the maintenance logbooks revealed that an annual inspection was accomplished on the day before the accident and that the engine was determined to be in an airworthy condition. At the time of the inspection, the airframe had a total time of 21,096 hours, and the engine had a total time of 15,415 hours of total time. Postaccident examination of the helicopter found that the cabin area and windshield structure were bent and distorted. The tailboom separated near the midsection, and the main rotor blades were buckled in multiple areas. The examination of the airframe and engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation. The engine was shipped to the manufacturer for further examination, which found that fuel was present throughout the engine fuel system, including the spray nozzle. A test run showed that the engine was capable of producing sufficient power. ## Aircraft - Registration: [N5334V](https://openairdocs.org/deregistered/N5334V-2022-08-11), registration cancelled 2022-08-11, S/N 2008, built 1959 (OpenAirDocs) - Reported make and model: HILLER UH-12E - Registry model: [Hiller UH-12E](https://openairdocs.org/model/hiller-uh-12e) (registry code 4360122) (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: 2008 - Year built: 1959 - Airframe hours: 21096 - Engines: ROLLS-ROYC 250-C20B 420 horsepower turbo shaft - Damage: Substantial damage - Flight: Aerial application, Part 137 - Operator: Western Helicopter Services - Registered owner: Bank Of Utah Trustee - Airworthiness certificate: Special, Restricted (Special) - Last inspection: 100 hour, September 22, 2021, 5.8 hours before - Equipment: Unknown ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 26; injuries: none; commercial; medical: class 2, without waivers/limitations; seat: center; restraint: 4-point; flight hours: 450 total, 46 in this make and model, 380 as pilot in command ## Weather - Conditions: Visual (VMC), Day - Wind: 230° at 5 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 68 °F, dew point 41 °F - Altimeter: 30.26 inHg - Icing: Unknown - Turbulence: Unknown - Observed at: KPUW, 34 nm away - METAR: KPUW 232153Z AUTO 23005KT 10SM CLR 20/05 A3026 RMK AO2 SLP242 T02000050 ## 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 20210923021959A](https://openairdocs.org/incident/20210923021959A), Sep 23, 2021: Hiller UH-12E, Bovill, ID, Substantial damage. The helicopter, operating part 137, was approximately 50' AGL and slowly approaching the loading zone to reload. The pilot felt a jolt then experienced a… ## Docket (9 files) The files NTSB released with the investigation on June 14, 2023, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=103976. 16.3 MB in all. - Pilot/operator aircraft accident report, NTSB form 6120.1 (item 1, PDF, 11 pages, 2.0 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=12809881&FileExtension=pdf&FileName=6120%20Docket_Redacted-Rel.pdf - Pilot statement (item 2, PDF, 2 pages, 156 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=15437064&FileExtension=pdf&FileName=Pilot-Written%20statement_Redacted-Rel.pdf - Record of memorandum-pilot (item 3, PDF, 1 page, 68 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=15436783&FileExtension=pdf&FileName=ROM-Pilot-%20Statement-Rel.pdf - Record of memorandum-truck personnel (item 4, PDF, 1 page, 61 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=15436819&FileExtension=pdf&FileName=ROM-Fertilizer%20Truck%20Personel-%20Statement-Rel.pdf - Photo array-onsite photos (item 5, PDF, 4 pages, 2.7 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=15390691&FileExtension=pdf&FileName=Onsite%20Photos-Courtesy%20of%20the%20WHS-Rel.pdf - Statement of party representatives to NTSB investigation-rolls royce (item 6, PDF, 1 page, 699 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=15592172&FileExtension=pdf&FileName=NTSB%20-%20Party%20Form%20-%20WPR21LA354%20-%20Bovill%20ID_Redacted-Rel.pdf - NTSB wreckage examination factual report (item 7, PDF, 12 pages, 17 photos, 1.9 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=15427140&FileExtension=pdf&FileName=WPR21LA354%20Examination%20Report-Rel.pdf - Rolls-royce engine investigation report (item 8, PDF, 10 pages, 13 photos, 8.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=15431359&FileExtension=pdf&FileName=WPR21LA354%20-%20Rolls-Royce%20Engine%20Report%20-%20Western%20Helicopters%20-%20Hiller%20UH-12D%20-%20N5334V-Rel.pdf - Email-wreckage release form (item 9, PDF, 3 pages, 347 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=15592643&FileExtension=pdf&FileName=Email-Wreckage%20Release%20Form_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.