# NTSB CEN14LA312: Airbus Helicopters AS-350B2, N407EM, Texarkana, TX, June 23, 2014 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: June 23, 2014, 13:45 local (18:45 UTC) - Place: Texarkana, TX - Coordinates: 33.535556, -94.192497 - Nearby events: https://openairdocs.org/map.md?lat=33.5356&lon=-94.1925&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Defining event: [Enroute: Powerplant sys/comp malf/fail](https://openairdocs.org/ntsb-events/340) - Highest injury: No injuries - Injuries: 4 uninjured - Status: Completed, report May 16, 2016 - Report: Approved by Office Director - NTSB office: Central Region - Parties: Honeywell, FAA FSDO, BEA, Eagle Med, LLC - NTSB case key (mKey): 89520 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CEN14LA312 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/89520/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=89520 - Page: https://openairdocs.org/ntsb/CEN14LA312 ## Probable cause The failure of the two fuel control unit drive bearings for reasons that could not be determined based on the available evidence, which resulted in an uncommanded engine acceleration and subsequent overspeed condition. Contributing to the accident was the pilot’s improper autorotation, which resulted in a hard landing. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Engine fuel and control: fuel controlling system](https://openairdocs.org/ntsb-findings/01057320): Aircraft › Aircraft power plant · Failure (probable cause); cases with it: [All aircraft, 59 cases](https://openairdocs.org/ntsb-findings/01057320/cases.md) - [Use of equip/info: aircraft control](https://openairdocs.org/ntsb-findings/02063040): Personnel issues › Task performance · Pilot (probable cause); cases with it: [All aircraft, 9,295 cases](https://openairdocs.org/ntsb-findings/02063040/cases.md) - [Performance/control parameters: descent/approach/glide path](https://openairdocs.org/ntsb-findings/01062040): Aircraft › Aircraft oper/perf/capability · Not attained/maintained (probable cause); cases with it: [All aircraft, 809 cases](https://openairdocs.org/ntsb-findings/01062040/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Enroute: Powerplant sys/comp malf/fail](https://openairdocs.org/ntsb-events/340) (defining event); cases with it: [All aircraft, 820 cases](https://openairdocs.org/ntsb-events/340/sequence.md) - [Autorotation: Hard landing](https://openairdocs.org/ntsb-events/092); cases with it: [All aircraft, 2,102 cases](https://openairdocs.org/ntsb-events/092/sequence.md) ## Analysis The commercial pilot and two flight crewmembers were conducting an emergency medical services flight. The helicopter was in cruise flight when the pilot noticed that the rotor rpm had rapidly increased and that the high rotor aural warning had sounded. Despite troubleshooting efforts, the pilot was unable to reduce the rotor rpm, so he performed on autorotation to a field. During the subsequent run-on landing, the helicopter touched down hard. During the landing, the main rotors contacted and partially severed the tailboom. Disassembly of the fuel control unit (FCU) revealed that the two drive bearings that ensure drive integrity between the FCU and the fuel pump had failed. The failure of the bearings led to excessive wear in the races and degraded the drive shaft such that it could no longer provide positive drive to the FCU, which the FCU interpreted as an underspeed condition. This led the FCU to command more power to the engine and resulted in an engine overspeed condition. Metallurgical testing of the FCU drive bearings did not reveal the reason for their failure. As a result of this accident, the engine manufacturer adjusted the FCU bearing replacement schedule from a one-time replacement to replacement every 600 hours. ## Factual narrative On June 23, 2014, about 1345 central daylight time, an Airbus Helicopters AS-350B2, N407EM, was substantially damaged following an autorotation near Texarkana, Texas. The commercial pilot, two crew members, and passenger were not injured. The helicopter was registered to and operated by EagleMed LLC under the provisions of 14 Code of Federal Regulations Part 135 as an emergency medical services flight. Visual meteorological conditions prevailed for the flight, which operated on a visual flight rules flight plan. The flight originated from Idabel, Oklahoma, about 1320, and was destined for Texarkana, Texas.According to statements provided by the pilot and medical crew, the helicopter was in cruise flight about 1,000 feet above ground level and five minutes from landing at the destination hospital when the pilot noticed the helicopter's rotor RPM rapidly increase with the associated high rotor aural warning. The pilot attempted to troubleshoot the malfunction before deciding to perform an autorotation to a farm field. During the run-on landing from the autorotation, the helicopter skipped and settled firmly to the ground. The main rotors contacted and partially severed the tail boom resulting in substantial damage. Damage to the front of the left skid was also found. The engine was removed from the helicopter and sent to Honeywell's laboratories in Phoenix, Arizona. Under the auspices of the Federal Aviation Administration (FAA), the engine was examined and placed on a test bed for the purpose of an engine run. The engine started and idled for 8 seconds before performing an uncommanded acceleration. The engine run was then terminated. Three subsequent engine runs were performed isolating various connections in order to troubleshoot the uncommanded acceleration command. Only when the pg line from the fuel control unit (FCU) to the power turbine (PT) was removed, did the engine not experience an uncommanded acceleration. The FCU was removed from the engine and inspected. The drive bearing appeared to be degraded and no longer provided axial or radial positioning of the FCU drive shaft. The splined fuel pump to FCU coupler spun freely on the FCU drive shaft. The fuel pump was inspected and debris and three bearing balls from the FCU were removed from the fuel pump overboard drain passage. The fuel pump was then sent to Triumph for additional testing. The additional testing found no defects with the fuel pump. Disassembly of the FCU revealed that the drive bearings failed. Metallurgy analysis of the FCU bearings and particulates found evidence of polyimide material in particles located during the FCU removal. The bearing separators are constructed of a porous polyimide material. Particles rich in silicon and oxygen were found imbedded in ball contact surfaces of the drive bearing inner and out races in addition to being found imbedded in undamaged bearing balls. Bearing balls that were recovered from the drain passage were dented and covered withaluminum rich material. No material anomalies were detected in the components. The reason for the failure of the drive bearing could not be determined. On December 18, 2014, Honeywell Service Bulletin LT 101-73-20-0272 was amended to change a onetime replacement of the main drive bearings to every 600 hours. A search of the FAA's Service Difficulty Reporting Site did not find any reports of part failure after the issuance of the updated service bulletin. ## Aircraft - Registration: N407EM (not matched to a registry record) - Reported make and model: AIRBUS HELICOPTERS AS-350B2 - Category: Helicopter - Serial number: 1906 - Year built: 1986 - Airframe hours: 10504 - Engines: Honeywell LTS 101-700-D 732 horsepower turbo shaft - Damage: Substantial damage - Flight: Part 135 - Operator: Eaglemed LLC, doing business as Eaglemed LLC - Registered owner: Eaglemed LLC - Airworthiness certificate: Standard, Normal - Last inspection: 100 hour, June 17, 2014, 40 hours before - Departed: Idabel, OK - Destination: Texarkana, TX - Flight plan: Company VFR ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 38; injuries: none; airline transport, military; instrument ratings: helicopter; medical: class 2, without waivers/limitations; last flight review June 1, 2013; seat: left; restraint: 4-point; flight hours: 2,285 total, 708 in this make and model, 2,072 as pilot in command, 65 in the last 90 days, 13 in the last 30 days, 4 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 180° at 11 knots, gusting 20 - Visibility: 9 statute miles - Lowest ceiling: none - Temperature: 84 °F, dew point 73 °F - Altimeter: 29.86 inHg - Observed at: KTXK, 11 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 20140623018259A](https://openairdocs.org/incident/20140623018259A), Jun 23, 2014: Eurocopter France AS350B2, Texarkana, TX, Substantial damage. On June 23, 2014, about 1345 central daylight time, an Airbus helicopters AS-350B2, N407EM, was substantially damaged following an autorotation near Texarkana,… ## Docket (5 files) The files NTSB released with the investigation on March 8, 2016, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=89520. 2.5 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 1.7 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40437443&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Master.PDF - Crew Statements (item 2, .PDF, 128 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40437444&FileExtension=.PDF&FileName=Crew%20Statements-Master.PDF - Party Form (item 3, .PDF, 308 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40437445&FileExtension=.PDF&FileName=Party%20Form-Master.PDF - Summary of Findings (item 4, .PDF, 65 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40437446&FileExtension=.PDF&FileName=Summary%20of%20Findings-Master.PDF - Accident Site Photo (item 5, .PDF, 1 photo, 357 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40437447&FileExtension=.PDF&FileName=Accident%20Site%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.