# NTSB CEN12LA525: Bell 214ST, N409SB, Avalon, TX, August 7, 2012 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: August 7, 2012, 08:45 local (13:45 UTC) - Place: Avalon, TX - Coordinates: 32.273887, -96.76583 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=32.2739&lon=-96.7658&mi=10 - Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping) - Defining event: [Maneuvering: Flight control sys malf/fail](https://openairdocs.org/ntsb-events/333) - Highest injury: No injuries - Injuries: 2 uninjured - Status: Completed, report March 24, 2014 - Report: Approved by Office Director - NTSB office: Central Region - Parties: FAA FSDO, Bell Helicopter, Inc - NTSB case key (mKey): 84595 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CEN12LA525 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/84595/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=84595 - Page: https://openairdocs.org/ntsb/CEN12LA525 ## Probable cause Maintenance personnel’s failure to properly torque the retaining nut and install the cotter pin that secured the helicopter’s tail rotor counterweight bellcrank. Contributing to the accident was the lack of detailed maintenance records that documented previous maintenance actions. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Tail rotor drive system: tail rotor drive shaft](https://openairdocs.org/ntsb-findings/01046510): Aircraft › Aircraft propeller/rotor · Failure (probable cause); cases with it: [Bell Helicopter Textron 214ST, 1 case](https://openairdocs.org/ntsb-findings/01046510/cases.md?model=1182126), [All aircraft, 25 cases](https://openairdocs.org/ntsb-findings/01046510/cases.md) - [Maintenance: installation](https://openairdocs.org/ntsb-findings/02062035): Personnel issues › Task performance · Maintenance personnel (probable cause); cases with it: [Bell Helicopter Textron 214ST, 1 case](https://openairdocs.org/ntsb-findings/02062035/cases.md?model=1182126), [All aircraft, 371 cases](https://openairdocs.org/ntsb-findings/02062035/cases.md) - [Documentation/record keeping: maintenance records](https://openairdocs.org/ntsb-findings/04033025): Organizational issues › Support/oversight/monitoring · Operator (probable cause); cases with it: [Bell Helicopter Textron 214ST, 1 case](https://openairdocs.org/ntsb-findings/04033025/cases.md?model=1182126), [All aircraft, 16 cases](https://openairdocs.org/ntsb-findings/04033025/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Maneuvering: Flight control sys malf/fail](https://openairdocs.org/ntsb-events/333) (defining event); cases with it: [Bell Helicopter Textron 214ST, 1 case](https://openairdocs.org/ntsb-events/333/sequence.md?model=1182126), [All aircraft, 410 cases](https://openairdocs.org/ntsb-events/333/sequence.md) - [Maneuvering: Part(s) separation from AC](https://openairdocs.org/ntsb-events/338); cases with it: [Bell Helicopter Textron 214ST, 1 case](https://openairdocs.org/ntsb-events/338/sequence.md?model=1182126), [All aircraft, 563 cases](https://openairdocs.org/ntsb-events/338/sequence.md) - [Landing: Off-field or emergency landing](https://openairdocs.org/ntsb-events/440); cases with it: [Bell Helicopter Textron 214ST, 1 case](https://openairdocs.org/ntsb-events/440/sequence.md?model=1182126), [All aircraft, 3,365 cases](https://openairdocs.org/ntsb-events/440/sequence.md) - [Landing-flare/touchdown: Roll over](https://openairdocs.org/ntsb-events/097); cases with it: [Bell Helicopter Textron 214ST, 1 case](https://openairdocs.org/ntsb-events/097/sequence.md?model=1182126), [All aircraft, 261 cases](https://openairdocs.org/ntsb-events/097/sequence.md) ## Analysis The helicopter was on its third test flight when the tail rotor 90-degree gearbox broke in two and separated from the helicopter. The crew conducted an autorotation to a field, and the helicopter came to rest on its side. Examination of the helicopter and components revealed that one of the tail rotor's two counterweight bellcranks and associated hardware were missing. Impact marks consistent with a counterweight bellcrank were found at the base of its associated tail rotor blade and on the aft right side of the helicopter. The remaining counterweight bellcrank was in place; however, the cotter pin for the castellated nut was missing. A review of the aircraft maintenance records revealed that the tail rotor assembly had been removed and reinstalled after the installation of test instrumentation. The maintenance records lacked specific details on whether the unit and its components were previously handled as a subassembly or as individual components when the tail rotor assembly was initially removed. Because the records did not indicate whether the unit should be handled as individual parts, the tail rotor was reinstalled as a complete subassembly, meaning that individual components, such as the nut and cotter pin, were not individually inspected before or after reinstallation on the helicopter. Reinstalling the tail rotor assembly in this manner led to the counterweight bellcrank retaining nut not being properly torqued and secured with a cotter pin. ## Factual narrative On August 7, 2012, about 0845 central daylight time, a Bell 214ST helicopter, N409SB, experienced a loss of tail rotor authority near Avalon, Texas. The commercial and airline transport pilots were not injured during the precautionary landing, and the helicopter was substantially damaged. The helicopter was owned and operated by Bell Helicopter, Textron, Inc. Fort Worth, Texas, under the provisions of 14 Code of Federal Regulations Part 91 as a research and development flight. Day visual meteorological conditions prevailed for the local flight which operated without a flight plan. The local flight originated from the Arlington Municipal Airport (KGKY), Arlington, Texas at 0815. According to the pilots the purpose of the flight was to collect data on the helicopter's rotor system. During the flight test, the helicopter completed a right turn and as they were setting up for another test condition, the pilot's heard a "bang," and felt the helicopter yaw. The pilot of the chase aircraft reported that something had departed the tail of the helicopter. The accident pilots then initiated an autorotation to a nearby field; however, helicopter yawed, rolled right, and came to rest on its side. The helicopter, the tail rotor gear box, and tail rotor blades were recovered and transported back to a Bell facility. Representatives from the NTSB, Federal Aviation Administration (FAA), and Bell Helicopter, then examined the helicopter and components at the manufacturer's facility. The tail rotor's 90-degree gear box was broken in two; one of the mast's two counterweight bellcranks and associated hardware were missing (and not located/recovered from the accident site); the remaining counterweight bellcrank remained attached. Examination of the remaining counterweight bellcrank, revealed that the assembly was in place, but "loose". The dustcap/grease cover for the remaining counterweight bellcrank was removed, exposing the castellated nut. The examination found that the nut's cotterpin was missing. Both tail rotor blades' attachments remained in place; both blades had separated outboard of their respective attachments. On the side with the missing counterweight bellcrank, impact marks consistent with the size and shape of a counterweight bellcrank, were found on the edge and base of its associated tail rotor blade, as well as on the right side of the helicopter. The rotor blade was torn in two, with the separation starting near the impact marks at the base of the blade. Since the accident helicopter was used to collect data on a new rotor system, the tail rotor blades and components had been removed to install test instrumentation. A review of the helicopters' maintenance workbook revealed the temporary re-installation of the instrumented tail rotor section. However, the maintenance entry was not specific as to whether the reinstallation of the instrumented tail rotor assembly was conducted as an assembly or as individual components. The mechanics installing theinstrumented tail rotor treated the unit as a complete sub-assembly and not as individual components. The difference meant that the individual components were not assembled or inspected, prior to or after installation onto the helicopter. The helicopter was on its third flight after the reinstallation of the instrumented tail rotor system and had accumulated about 2.8 flight hours, before the accident. ## Aircraft - Registration: [N409SB](https://openairdocs.org/deregistered/N409SB-2015-06-25), registration cancelled 2015-06-25, S/N 28199, built 1990 (OpenAirDocs) - Reported make and model: BELL 214ST - Registry model: [Bell Helicopter Textron 214ST](https://openairdocs.org/model/bell-helicopter-textron-214st) (registry code 1182126) (OpenAirDocs) - Registry engine: [GE CT7 series](https://openairdocs.org/engine/ge-ct7-series) (registry code 30030, turbo-shaft) (OpenAirDocs) - Category: Helicopter - Serial number: 28199 - Engines: General Electric CT7-2A turbo shaft; General Electric CT7-2A turbo shaft - Damage: Substantial damage - Flight: Flight test, Part 91 - Operator: Bell Helicopter Textron Inc - Registered owner: Bell Helicopter Textron Inc - Airworthiness certificate: Special, Experimental (Special) - Departed: KGKY, Arlington Muni, TX - Destination: KGKY, Arlington Muni, TX - Flight plan: Company VFR - Equipment: Data recorder ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 52; injuries: none; flight instructor, commercial; airplane ratings: single-engine land, multi-engine land; instrument ratings: helicopter, airplane, powered-lift; medical: class 2, with waivers/limitations; seat: right; flight hours: 6,597 total, 2.7 in this make and model, 3,918 as pilot in command, 18.7 in the last 90 days, 5.3 in the last 30 days, 0.6 in the last 24 hours - Co-pilot; age 39; injuries: none; flight instructor, airline transport, commercial; airplane ratings: multi-engine land, single-engine land; instrument ratings: helicopter, airplane; medical: class 2, without waivers/limitations; last flight review April 15, 2012; seat: left; flight hours: 3,100 total, 2.7 in this make and model, 2,600 as pilot in command, 35 in the last 90 days, 12 in the last 30 days, 0.6 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Visibility: 10 statute miles - Temperature: 84 °F, dew point 66 °F - Altimeter: 29.96 inHg - Observed at: KGKY ## 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 20120807018389A](https://openairdocs.org/incident/20120807018389A), Aug 7, 2012: Bell 214ST, Avalon, TX, Substantial damage. Aircraft N409SB departed kgky on a flight test plan for a new rotor system to be installed in the Bell 525. The aircraft was on it's 3rd flight test. They… ## Docket (6 files) The files NTSB released with the investigation on February 3, 2014, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=84595. 8.3 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 2.4 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40403060&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Redacted.PDF - Pilot/Operator statements (item 2, .PDF, 887 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40403061&FileExtension=.PDF&FileName=Pilot%2FOperator%20statements-Redacted.PDF - Statement of Party Representatives to NTSB Investigation (item 3, .PDF, 216 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40403062&FileExtension=.PDF&FileName=Statement%20of%20Party%20Representatives%20to%20NTSB%20Investigation-Redacted.PDF - Photo 1: Accident helicopter (non NTSB photo) (item 4, .PDF, 3.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40403113&FileExtension=.PDF&FileName=Photo%201%3A%20%20Accident%20helicopter%20%20%20%20%20(non%20NTSB%20photo)-Master.PDF - Photo 2: Tailrotor bell crank (item 5, .PDF, 812 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40403116&FileExtension=.PDF&FileName=Photo%202%3A%20Tailrotor%20bell%20crank-Master.PDF - Photo 3: Counterweight nut (item 6, .PDF, 695 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40403134&FileExtension=.PDF&FileName=Photo%203%3A%20Counterweight%20nut-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.