# NTSB WPR10LA117: Bell 47G-4A, N28938, Shafter, CA, January 22, 2010 - Type: NTSB accident investigation - Classification: Accident · Minor injuries · Limited investigation · Final report - Date: January 22, 2010, 09:09 local (17:09 UTC) - Place: Shafter, CA - Coordinates: 35.473331, -119.242774 - Nearby events: https://openairdocs.org/map.md?lat=35.4733&lon=-119.2428&mi=10 - Phase of flight: [Landing](https://openairdocs.org/ntsb-phases/550) (OpenAirDocs' grouping) - Defining event: [Landing-flare/touchdown: Hard landing](https://openairdocs.org/ntsb-events/092) - Highest injury: Minor injuries - Injuries: 1 minor - Status: Completed, report January 7, 2011 - Report: Approved by Office Director - NTSB office: Western Pacific Region - Parties: Federal Aviation Administration FSDO - NTSB case key (mKey): 75301 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR10LA117 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/75301/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=75301 - Page: https://openairdocs.org/ntsb/WPR10LA117 ## Probable cause The loss of a main rotor blade counterweight due to corrosion. Contributing to the accident was the failure of the operator to perform the initial and recurrent inspections required by a Service Bulletin to detect the corrosion in the counterweight. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Flight control system](https://openairdocs.org/ntsb-findings/01022700): Aircraft › Aircraft systems · Failure (probable cause); cases with it: [Bell 47G-4A, 1 case](https://openairdocs.org/ntsb-findings/01022700/cases.md?model=1181031), [All aircraft, 65 cases](https://openairdocs.org/ntsb-findings/01022700/cases.md) - [Inspection](https://openairdocs.org/ntsb-findings/02061500): Personnel issues › Task performance · Maintenance personnel (probable cause); cases with it: [Bell 47G-4A, 1 case](https://openairdocs.org/ntsb-findings/02061500/cases.md?model=1181031), [All aircraft, 29 cases](https://openairdocs.org/ntsb-findings/02061500/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Prior to flight: Aircraft maintenance event](https://openairdocs.org/ntsb-events/040); cases with it: [Bell 47G-4A, 1 case](https://openairdocs.org/ntsb-events/040/sequence.md?model=1181031), [All aircraft, 484 cases](https://openairdocs.org/ntsb-events/040/sequence.md) - [Maneuvering: Part(s) separation from AC](https://openairdocs.org/ntsb-events/338); cases with it: [Bell 47G-4A, 1 case](https://openairdocs.org/ntsb-events/338/sequence.md?model=1181031), [All aircraft, 563 cases](https://openairdocs.org/ntsb-events/338/sequence.md) - [Landing-flare/touchdown: Hard landing](https://openairdocs.org/ntsb-events/092) (defining event); cases with it: [Bell 47G-4A, 4 cases](https://openairdocs.org/ntsb-events/092/sequence.md?model=1181031), [All aircraft, 2,102 cases](https://openairdocs.org/ntsb-events/092/sequence.md) ## Analysis The pilot reported that he was maneuvering the helicopter to make an aerial application pass. At approximately 80 feet above ground level, he heard a muffled "crack/bang" and the helicopter immediately yawed and he experienced lateral vibrations in the cyclic. The pilot then initiated a forced landing with the shaking becoming more violent. The helicopter subsequently landed hard with the engine still running. The main rotor blades contacted and severed the tail boom, and the engine separated from its mounts. Postaccident examination of the helicopter revealed that a main rotor counterweight was missing. Examination of the broken counterweight rod end showed evidence of corrosion over approximately 45 percent of the diameter of the rod end. Maintenance records indicate that a Service Bulletin to inspect main rotor counterweight rods for pit corrosion had not been complied with. The Service Bulletin states that after an initial inspection of the main rotor counterweight rods, recurrent inspections should be accomplished every 300 hours of time in service. ## Factual narrative On January 22, 2010, approximately 0909 Pacific standard time, a Bell 47G-4A helicopter, N28938, sustained substantial damage following a forced landing near Shafter, California. The commercial pilot, the sole occupant, received minor injuries. Inland Crop Dusters, Inc., was operating the helicopter under the provisions of 14 Code of Federal Regulations Part 137. Visual meteorological conditions prevailed for the aerial application flight. A flight plan had not been filed. The pilot reported that while maneuvering at 80 feet to make an aerial application run, he heard a muffled "crack/bang." The helicopter immediately yawed and the pilot experienced lateral vibrations in the cyclic. He initiated a forced landing to the field below and the shaking became more "violent." He said the engine was still running, but the aircraft landed hard. The main rotor blades contacted and severed the tail boom, and the engine separated from its mounts. A post accident examination of the helicopter by a Federal Aviation Administration inspector revealed that a main rotor blade counterweight was missing. There was a search for the missing part, but it was never located. Examination of the broken counterweight rod end showed evidence of corrosion over approximately 45 percent of the diameter of the rod end. Maintenance records indicate the rod was not inspected for corrosion pits to comply with Bell Helicopter Textron Service Bulletin 47-78-2 Rev. B, April 13, 1981. The Service Bulletin states that after an initial inspection for corrosion pits on the counterweight rods, recurrent inspections will be accomplished every 300 hours of time in service. ## Aircraft - Registration: [N28938](https://openairdocs.org/deregistered/N28938-2018-03-02), registration cancelled 2018-03-02, S/N 7728, built 1970 (OpenAirDocs) - Reported make and model: BELL 47G-4A - Registry model: [Bell 47G-4A](https://openairdocs.org/model/bell-47g-4a) (registry code 1181031) (OpenAirDocs) - Registry engine: [Lycoming VO-540 series](https://openairdocs.org/engine/lycoming-vo-540-series) (registry code 41534, reciprocating) (OpenAirDocs) - Category: Helicopter - Serial number: 7728 - Airframe hours: 7207 - Engines: LYCOMING VO-540 SERIES 310 horsepower reciprocating - Damage: Substantial damage - Flight: Aerial application, Part 137 - Operator: Inland Crop Dusters Inc - Registered owner: Inland Crop Dusters Inc - Airworthiness certificate: Special, Restricted (Special) - Departed: MIT, Shafter, CA - Destination: MIT, Shafter, CA ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 63; injuries: minor; commercial; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 2, with waivers/limitations; seat: right; flight hours: 32,000 total, 4,000 in this make and model, 31,280 as pilot in command ## Weather - Conditions: Visual (VMC), Day - Wind: 90° at 7 knots - Visibility: 10 statute miles - Lowest ceiling: 4,400 ft broken - Temperature: 46 °F, dew point 39 °F - Altimeter: 29.45 inHg - Observed at: BFL, 10 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 20100122026059A](https://openairdocs.org/incident/20100122026059A), Jan 22, 2010: Bell 47G-4A, Shafter, CA, Substantial damage. Pilot stated he was nearing his first aerial application pass traveling in a northwest direction, turning and decending. Approximate altitude of 80 feet and… ## Other investigations on N28938 (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 LAX87DVD01](https://openairdocs.org/ntsb/LAX87DVD01), Feb 2, 1987: Bell 47G4A (N28938), Stockton, CA, substantial damage ## Docket (5 files) The files NTSB released with the investigation on September 29, 2010, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=75301. 3.8 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 457 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40336840&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Redacted.PDF - FAA Report-Interviews (item 2, .PDF, 2.9 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40336841&FileExtension=.PDF&FileName=FAA%20Report-Interviews-Redacted.PDF - Release of Aircraft Wreckage, NTSB Form 6120.15 (item 3, .PDF, 68 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40336842&FileExtension=.PDF&FileName=Release%20of%20Aircraft%20Wreckage,%20NTSB%20Form%206120.15-Redacted.PDF - Bell Service Bulletin 47-78-2 (item 4, .PDF, 360 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40336843&FileExtension=.PDF&FileName=Bell%20Service%20Bulletin%2047-78-2-Master.PDF - Bell 47, Proposed AD, with 1 Embedded Photo (item 5, .PDF, 58 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40336844&FileExtension=.PDF&FileName=Bell%2047,%20Proposed%20AD,%20with%201%20Embedded%20Photo-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.