# NTSB CEN09IA003: MD Helicopter MD 900, N902RN, Weatherford, TX, October 8, 2008 - Type: NTSB incident investigation - Classification: Incident · No injuries · Incident investigation · Final report - Date: October 8, 2008, 14:10 local (19:10 UTC) - Place: Weatherford, TX - Coordinates: 32.746112, -97.68222 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=32.7461&lon=-97.6822&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Defining event: [Enroute-cruise: Flight control sys malf/fail](https://openairdocs.org/ntsb-events/333) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report November 9, 2009 - Report: Approved by Office Director - NTSB office: Central Region - Parties: MD Helicopters - ADs cited in the narratives: [AD 2008-22-53](https://openairdocs.org/ad/2008-22-53) (OpenAirDocs) - NTSB case key (mKey): 69244 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CEN09IA003 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/69244/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=69244 - Page: https://openairdocs.org/ntsb/CEN09IA003 ## Probable cause The failure of the vertical stabilizer control adapter due to reverse bending fatigue. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Flight control system: stabilizer control system](https://openairdocs.org/ntsb-findings/01022740): Aircraft › Aircraft systems · Fatigue/wear/corrosion (probable cause); cases with it: [MD Helicopters MD 900, 2 cases](https://openairdocs.org/ntsb-findings/01022740/cases.md?model=3030004), [All aircraft, 13 cases](https://openairdocs.org/ntsb-findings/01022740/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Enroute-cruise: Flight control sys malf/fail](https://openairdocs.org/ntsb-events/333) (defining event); cases with it: [MD Helicopters MD 900, 3 cases](https://openairdocs.org/ntsb-events/333/sequence.md?model=3030004), [All aircraft, 410 cases](https://openairdocs.org/ntsb-events/333/sequence.md) ## Analysis While in cruise flight, the helicopter experienced a hard right yaw and subsequent left nose tuck. The pilot was able to regain control of the helicopter and reduce the airspeed to under 100 knots. The flight continued to its destination without further incident. An examination revealed that the vertical stabilizer control system adapter failed. Metallurgical examination revealed that the failure mode was reverse bending fatigue. The vertical stabilizer control system adapter has since been redesigned. Installation of the improved design is now required by an Airworthiness Directive. ## Factual narrative On October 8, 2008, approximately 1410 central daylight time, an McDonnell Douglas Helicopter Inc., MD 900, N902RN, piloted by a commercial pilot, experienced a violent yaw while in cruise flight near Weatherford, Texas. Visual meteorological conditions prevailed at the time of the event. The positioning flight was being operated under the provisions of Title 14 Code of Federal Regulations Part 91 without a flight plan. The pilot was not injured. The flight was en route to Grand Prairie Municipal Airport (KGPM), Grand Prairie, Texas. According to the written statement submitted by the pilot, he had stopped in Plainview, Texas, for fuel, and was en route to KGPM at an altitude of 5,500 feet mean sea level. The pilot stated that there was a “right quartering tailwind” approximately 15 knots, the sky condition was clear, and there was no turbulence. The airspeed was 125 knots indicated airspeed and the autopilot was “engaged and coupled to [altitude] and [navigation] modes.” One hour and thirty-five minutes into the flight the helicopter experienced a “hard right yaw and subsequent left nose tuck.” The pilot was able to regain control of the helicopter and reduced the airspeed “below 100” knots. The flight continued to KGPM without further incident. The helicopter was examined under the supervision of National Transportation Safety Board (NTSB) investigators and a representative from MD Helicopters. The examination revealed that the adapter located between the actuator and the control rod for the left vertical stabilizer control system (VSCS) had fractured. Further examination revealed minor damage to the front and rear fairings located between the upper and lower fins and a small rub mark on the leading edge of the horizontal stabilizer. With the exception of the fractures, the actuation assembly was intact, correctly installed, and appropriately wire-locked. The actuator and the control rod rotated freely within the limitations of their respective rod-ends. Examination of the rigging of the right and left vertical fins revealed no anomalies. The left actuation assembly was removed from the helicopter and sent to the NTSB Materials Laboratory in Washington, D.C., for further examination. Examination of the fracture face on the adapter revealed two distinct opposing zones displaying crack arrest marks and ratchet marks, typical of reverse bending fatigue. A review of the maintenance records revealed that fractured adapter had been installed in September 2, 2008, in compliance with MDHI Service Bulletin (SB) 900-109, dated August 15, 2008. According to MDHI, at least three other helicopters encountered similar failures of the VSCS actuator, (Please reference NTSB case number SEA08SA170, DEN08RA132, and CEN09IA032) all within a six-month period of time. On October 17, 2008, MDHI issued SB 900-110 “Operational Restrictions Concerning VSCS Tube Adapters.” This SB was directed at all MD900 helicopters within a specific serial number range. The SBrequired owners and operators to reduce the operational airspeed of their helicopters to 100 knots indicated airspeed, or Velocity Never Exceed Speed (whichever was less), in visual meteorological conditions, with the autopilot off, VSCS on, until the VSCS adapters could be replaced. On December 3, 2008, MDHI issued SB 900-110R1 “Operational Restrictions and Replacement of VSCS Tube Adapters.” This SB superseded the SB 900-110 and directed operators to replace the two VSCS tube adapters with the “improved” tube adapters. Once this SB had been complied with, the operational airspeed and autopilot restrictions were no longer applicable. On December 17, 2008, Airworthiness Directive (AD) 2008-22-53 issued by the Federal Aviation Administration became effective. This AD required all MD900 helicopter operators with the old VSCS tube adapters to comply with airspeed and autopilot restrictions. If the operator had replaced the old VSCS tube adapter with the new “improved” design, the AD was not applicable. ## Aircraft - Registration: [N902RN](https://openairdocs.org/deregistered/N902RN-2012-12-17), registration cancelled 2012-12-17, S/N 900-00121, built 2007 (OpenAirDocs) - Reported make and model: MD Helicopter Inc MD 900 - Registry model: [MD Helicopters MD 900](https://openairdocs.org/model/md-helicopters-md-900) (registry code 3030004) (OpenAirDocs) - Registry engine: [Pratt & Whitney Canada PW207E](https://openairdocs.org/engine/pratt-whitney-canada-pw207e) (registry code 52161, turbo-shaft) (OpenAirDocs) - Category: Helicopter - Serial number: 900-00121 - Airframe hours: 201 - Engines: Pratt & Whitney Canada PW 207E 646 horsepower turbo shaft; Pratt & Whitney Canada PW 207E 646 horsepower turbo shaft - Damage: Minor damage - Flight: Positioning, Part 91 - Operator: California Shock and Trauma Air Rescue - Registered owner: California Shock and Trauma Air Rescue - Airworthiness certificate: Standard, Normal - Last inspection: Continuous airworthiness, September 25, 2008 - Departed: KPVW, Plainview, TX - Destination: KGPM, Grand Prairie, TX ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 48; injuries: none; commercial; airplane ratings: single-engine land; instrument ratings: helicopter; medical: class 2, with waivers/limitations; last flight review November 20, 2007; seat: left; flight hours: 5,600 total, 214 in this make and model, 5,200 as pilot in command, 44 in the last 90 days, 23 in the last 30 days, 9 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: calm - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 81 °F, dew point 46 °F - Altimeter: 30.04 inHg - Observed at: KMWL ## Docket (6 files) The files NTSB released with the investigation on June 15, 2009, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=69244. 8.0 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 502 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40302234&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Redacted.PDF - Materials Laboratory 15 - Factual Report 09-008. (item 2, .PDF, 981 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40309847&FileExtension=.PDF&FileName=Materials%20Laboratory%2015%20-%20Factual%20Report%2009-008.-Master.PDF - MD Service Bulletin 900-110 (item 3, .PDF, 5.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40313905&FileExtension=.PDF&FileName=MD%20Service%20Bulletin%20900-110-Master.PDF - MD Service Bulletin 900-110R1 (item 4, .PDF, 79 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40313906&FileExtension=.PDF&FileName=MD%20Service%20Bulletin%20900-110R1-Master.PDF - FAA Airworthiness Directive 2008-22-53 (item 5, .PDF, 34 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40313907&FileExtension=.PDF&FileName=FAA%20Airworthiness%20Directive%202008-22-53-Master.PDF - Statement of Party Representatives to NTSB Investigation (item 6, .PDF, 1.1 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40314302&FileExtension=.PDF&FileName=Statement%20of%20Party%20Representatives%20to%20NTSB%20Investigation-Redacted.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.