# NTSB CEN09IA032: MD Helicopter MD 900, N902NM, Amherst, TX, October 19, 2008 - Type: NTSB incident investigation - Classification: Incident · No injuries · Incident investigation · Final report - Date: October 19, 2008, 16:00 local (21:00 UTC) - Place: Amherst, TX - Coordinates: 34.050834, -102.466667 - Nearby events: https://openairdocs.org/map.md?lat=34.0508&lon=-102.4667&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: 4 uninjured - Status: Completed, report August 13, 2009 - Report: Approved by Office Director - NTSB office: Central Region - ADs cited in the narratives: [AD 2008-22-53](https://openairdocs.org/ad/2008-22-53) (OpenAirDocs) - NTSB case key (mKey): 69334 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CEN09IA032 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/69334/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=69334 - Page: https://openairdocs.org/ntsb/CEN09IA032 ## 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) ## Analysis While in cruise flight, the helicopter experienced a hard right yaw and subsequent pitching moment up and down. The pilot was able to regain control of the helicopter and land without further incident. Examination revealed that the left vertical stabilizer control system adapter had failed. Metallurgical examination revealed that the failure mode was reverse bending fatigue. The vertical stabilizer control system adapter has been replaced with an improved design. Further, the Federal Aviation Administration has issued an Airworthiness Directive (AD) requiring all MD900 helicopter operators with the old VSCS tube adapters to comply with airspeed and autopilot restrictions. If an operator replaces the old VSCS tube adapter with the new design, the AD is not applicable. ## Factual narrative On October 19, 2008, approximately 1600 central daylight time, an McDonnell Douglas Helicopter Inc MD 900, N902NM, piloted by an airline transport pilot and operated by Aero Care, experienced a violent yaw while in cruise flight near Amherst, Texas. Visual meteorological conditions prevailed at the time of the event. The positioning flight was being conducted under the provisions of Title 14 Code of Federal Regulations Part 91 without a flight plan. No injuries were reported. The flight was en route to Clovis, New Mexico, and had departed Lubbock, Texas, approximately 1528. According to the accident report form submitted by the operator, during cruise flight with the autopilot off, the helicopter encountered a violent yaw to the right. The pilot regained control of the helicopter and returned to Lubbock without further incident. An examination of the helicopter revealed that the left vertical stabilizer control rod had separated from the actuator at the adapter. The left actuator adapter was removed from the helicopter and sent to the NTSB Materials Laboratory in Washington, D.C., for further examination. Examination of the fracture face revealed two distinct opposing zones displaying crack arrest marks and ratchet marks, consistent with reverse bending fatigue. According to MDHI, at least three other helicopters encountered similar failures of the VSCS actuator, (Please reference NTSB case number SEA08SA170, DEN08RA132, and CEN09IA003) all within a six-month period of time. On October 17, 2008, MDHI issued Service Bulletin (SB) 900-110 “Operational Restrictions Concerning VSCS Tube Adapters.” This SB was directed at all MD900 helicopters within a specific serial number range. The SB required 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. Aero Care was in compliance with this SB at the time of their event. 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. ## 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) ## Aircraft - Registration: [N902NM](https://openairdocs.org/deregistered/N902NM-2009-12-23), registration cancelled 2009-12-23, S/N 900-00105, built 2002 (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: 900-00105 - Airframe hours: 2842 - Engines: Pratt & Whitney BG0058 turbo shaft; Pratt & Whitney BG0106 turbo shaft - Damage: Minor damage - Flight: Positioning, Part 91 - Operator: Covenant Health System, doing business as Aero Care - Registered owner: Covenant Health System - Airworthiness certificate: Standard, Normal - Last inspection: AAIP, September 26, 2008 - Departed: KLBB, Lubbock, TX - Destination: KCVN, Clovis, NM - Flight plan: Company VFR ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 58; injuries: none; commercial, airline transport; airplane ratings: single-engine land, multi-engine land; instrument ratings: helicopter, airplane; medical: class 2, with waivers/limitations; last flight review April 24, 2008; seat: right; flight hours: 10,000 total, 1,000 in this make and model, 9,900 as pilot in command ## Weather - Conditions: Visual (VMC), Day - Wind: variable at 11 knots - Visibility: 50 statute miles - Lowest ceiling: none - Temperature: 73 °F, dew point 52 °F - Altimeter: 30.18 inHg - Observed at: KCVN, 30 nm away ## Docket (5 files) The files NTSB released with the investigation on June 15, 2009, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=69334. 6.1 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 593 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40302883&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Redacted.PDF - MD Service Bulletin 900-110 (item 2, .PDF, 5.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40313909&FileExtension=.PDF&FileName=MD%20Service%20Bulletin%20900-110-Master.PDF - MD Service Bulletin 900-110R1 (item 3, .PDF, 79 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40313910&FileExtension=.PDF&FileName=MD%20Service%20Bulletin%20900-110R1-Master.PDF - FAA Airworthiness Directive 2008-22-53 (item 4, .PDF, 34 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40313912&FileExtension=.PDF&FileName=FAA%20Airworthiness%20Directive%202008-22-53-Master.PDF - Statement of Party Representatives to NTSB Investigation (item 5, .PDF, 128 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40314303&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.