# NTSB WPR18LA206: Bell UH 1H, N107CH, Oakdale, CA, July 24, 2018 - Type: NTSB accident investigation - Classification: Accident · Minor injuries · Class 3 · Limited · Final report - Date: July 23, 2018, 18:00 local (Jul 24, 2018, 01:00 UTC) - Place: Oakdale, CA - Coordinates: 37.798332, -120.722221 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=37.7983&lon=-120.7222&mi=10 - Phase of flight: [Landing](https://openairdocs.org/ntsb-phases/550) (OpenAirDocs' grouping) - Defining event: [Landing-flare/touchdown: Loss of control in flight](https://openairdocs.org/ntsb-events/240) - Highest injury: Minor injuries - Injuries: 1 minor, 1 uninjured - Status: Completed - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Western Pacific Region - Parties: FAA - NTSB case key (mKey): 97919 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR18LA206 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/97919/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=97919 - Page: https://openairdocs.org/ntsb/WPR18LA206 ## Probable cause The pilot's loss of control during a precautionary landing following an abnormal noise in-flight, the source of which could not be determined. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Performance/control parameters: directional control](https://openairdocs.org/ntsb-findings/01062020): Aircraft › Aircraft oper/perf/capability · Not attained/maintained (probable cause); cases with it: [Bell UH-1H, 1 case](https://openairdocs.org/ntsb-findings/01062020/cases.md?model=1181407), [All aircraft, 3,958 cases](https://openairdocs.org/ntsb-findings/01062020/cases.md) - [Performance/control parameters: landing flare](https://openairdocs.org/ntsb-findings/01062041): Aircraft › Aircraft oper/perf/capability · Not attained/maintained (probable cause); cases with it: [Bell UH-1H, 2 cases](https://openairdocs.org/ntsb-findings/01062041/cases.md?model=1181407), [All aircraft, 1,285 cases](https://openairdocs.org/ntsb-findings/01062041/cases.md) - [Use of equip/info: aircraft control](https://openairdocs.org/ntsb-findings/02063040): Personnel issues › Task performance · Pilot (probable cause); cases with it: [Bell UH-1H, 9 cases](https://openairdocs.org/ntsb-findings/02063040/cases.md?model=1181407), [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: [Bell UH-1H, 4 cases](https://openairdocs.org/ntsb-findings/05000000/cases.md?model=1181407), [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. - [Enroute-cruise: Miscellaneous/other](https://openairdocs.org/ntsb-events/900); cases with it: [Bell UH-1H, 2 cases](https://openairdocs.org/ntsb-events/900/sequence.md?model=1181407), [All aircraft, 1,556 cases](https://openairdocs.org/ntsb-events/900/sequence.md) - [Landing-flare/touchdown: Loss of control in flight](https://openairdocs.org/ntsb-events/240) (defining event); cases with it: [Bell UH-1H, 6 cases](https://openairdocs.org/ntsb-events/240/sequence.md?model=1181407), [All aircraft, 5,002 cases](https://openairdocs.org/ntsb-events/240/sequence.md) - [Landing-flare/touchdown: Collision with terr/obj (non-CFIT) ](https://openairdocs.org/ntsb-events/470); cases with it: [Bell UH-1H, 8 cases](https://openairdocs.org/ntsb-events/470/sequence.md?model=1181407), [All aircraft, 10,189 cases](https://openairdocs.org/ntsb-events/470/sequence.md) ## Analysis During a cross-country flight, the helicopter started to produce an unusual noise. The pilot initiated a precautionary landing and the noise became louder. About 5 ft off the ground before touchdown, the helicopter entered an uncontrolled climb and yaw. The pilot was unable to recover from the loss of directional control and the helicopter subsequently impacted terrain. Examination of fractured pieces from the main rotor drive shaft and the swashplate assembly exhibited features consistent with fracture from overstress; however, it is likely that this damage was sustained during the impact. Although it is possible that one of the components may have failed from overstress in-flight, this would have required an abnormally high load input to one or more components. The exam did not reveal any evidence of mechanical malfunctions or anomalies that would have precluded normal operation of the helicopter, and the source of the noise reported by the pilot could not be determined. ## Factual narrative On July 24, 2018, about 1800 Pacific daylight time, a Bell UH-1H helicopter, N107CH, was substantially damaged during a precautionary landing near Oakdale, California. The pilot was not injured; the passenger sustained minor injuries. The helicopter was registered to Airlift Helicopters Service and operated by the pilot under the provisions of Title 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed for the cross-country flight, and no flight plan was filed. The flight originated from Madera Municipal Airport (MAE), Madera, California at 1600 and was destined for Lincoln Regional Airport/Karl Harder Field (LHM), Lincoln, California. In a post-accident telephone conversation with the National Transportation Safety Board (NTSB) Investigator in Charge, the pilot stated that he was in a straight and level flight when he heard a "strange" noise and he decided to execute a precautionary landing. He described the noise sounding like "a tarp in the back of a pickup". There were no other indications in the helicopter; all instruments were within normal operating limits, there was no vibration and the engine was producing power. About 5 ft above the ground, the helicopter entered an uncontrolled climb and yaw. The pilot was unable to recover from the loss of directional control and the helicopter impacted terrain. In the NTSB Form 6120.1 "Pilot/Operator Aircraft Accident/Incident Report", the pilot added that, during the descent, the noise "grew louder". The helicopter touched down in the upright position. In the report, the pilot did not mention uncontrolled climb and/or yaw. In a telephone call to the Federal Aviation Administration (FAA) Inspector, the passenger in the helicopter reported that, while in a level cruise flight, he heard a noise. The pilot checked the instrument panel and confirmed that all instruments were within normal operating limits. The passenger noted no vibrations or changes other than the noise. He did not disclose how long the noise was present nor what the noise sounded like. They made a normal approach with a controlled descend to land and that was the last thing he remembered surrounding the accident sequence. The NTSB Materials Laboratory examined fractured pieces from the main drive shaft and damaged remnants of the swashplate assembly. The main drive shaft and the swashplate support fracture surfaces exhibited features consistent with fracture from overstress. The overstress orientation varied from part to part, but was observed in tension, bending, shear, compression, and combinations. Postacccident exam of the helicopter did not reveal any pre-exciting malfunction that would have precluded normal operations. ## Aircraft - Registration: [N107CH](https://openairdocs.org/aircraft/N107CH), registered now, S/N 67-17290, built 1967 (OpenAirDocs) - Reported make and model: Bell UH 1H (No Series) - Registry model: [Bell UH-1H](https://openairdocs.org/model/bell-uh-1h) (registry code 1181407) (OpenAirDocs) - Registry engine: [Lycoming T53-L-13](https://openairdocs.org/engine/lycoming-t53-l-13) (registry code 41551, turbo-shaft) (OpenAirDocs) - Category: Helicopter - Serial number: 67-17290 - Year built: 1967 - Airframe hours: 8905.8 - Engines: Honeywell T53 turbo shaft - Damage: Substantial damage - Flight: Ferry, Part 91 - Airworthiness certificate: Special, Restricted (Special) - Last inspection: Continuous airworthiness, May 21, 2018 - Departed: MAE, Madera, CA - Destination: LHM, Lincoln, CA ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 60; injuries: none; commercial; medical: class 2, without waivers/limitations; seat: left; restraint: 4-point ## Weather - Conditions: Visual (VMC), Day - Wind: 300° at 16 knots, gusting 22 - Visibility: 10 statute miles - Lowest ceiling: 11,000 ft broken - Temperature: 100 °F, dew point 55 °F - Altimeter: 29.89 inHg - Observed at: KMOD, 15 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 20180724014579A](https://openairdocs.org/incident/20180724014579A), Jul 24, 2018: Bell - Hagglund UH-1H, Oakdale, CA, Substantial damage. The accident occurred while repositioning to a new aerial fire fighting assignment for the state fire agency under a cwn contract order. In cruise flight at… ## Docket (6 files) The files NTSB released with the investigation on September 8, 2020, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=97919. 23.7 MB in all. - Materials Laboratory Factual Report (item 1, .PDF, 18.0 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40486708&FileExtension=.PDF&FileName=Materials%20Laboratory%20Factual%20Report-Master.PDF - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 2, .PDF, 3.1 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40486709&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Master.PDF - Record of Conversation - Pilot (item 3, .PDF, 84 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40486710&FileExtension=.PDF&FileName=Record%20of%20Conversation%20-%20Pilot-Master.PDF - FAA ROC Passenger (item 4, .PDF, 331 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40486711&FileExtension=.PDF&FileName=FAA%20ROC%20Passenger-Master.PDF - Release of Aircraft Wreckage, NTSB Form 6120.15 (item 5, .PDF, 226 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40486712&FileExtension=.PDF&FileName=Release%20of%20Aircraft%20Wreckage,%20NTSB%20Form%206120.15-Master.PDF - Photos (item 6, .PDF, 1.9 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40486713&FileExtension=.PDF&FileName=Photos-Master.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.