# NTSB CEN12LA242: Bell 407, N509MT, Aberdeen, SD, April 14, 2012 - Type: NTSB accident investigation - Classification: Accident · Minor injuries · Limited investigation · Final report - Date: April 14, 2012, 02:55 local (07:55 UTC) - Place: Aberdeen, SD - Coordinates: 45.466667, -98.476387 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=45.4667&lon=-98.4764&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: Minor injuries - Injuries: 1 minor - Status: Completed, report June 11, 2014 - Report: Approved by Office Director - NTSB office: Central Region - Parties: Rolls-Royce Engines, Transportation Safety Board of Canada, Federal Aviation Administration, Med-Trans Corp - NTSB case key (mKey): 83384 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CEN12LA242 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/83384/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=83384 - Page: https://openairdocs.org/ntsb/CEN12LA242 ## Probable cause The fatigue failure of two turbine engine blades due to vibration. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Engine (turbine/turboprop): turbine section](https://openairdocs.org/ntsb-findings/01057250): Aircraft › Aircraft power plant · Fatigue/wear/corrosion (probable cause); cases with it: [Bell 407, 3 cases](https://openairdocs.org/ntsb-findings/01057250/cases.md?model=1182206), [All aircraft, 74 cases](https://openairdocs.org/ntsb-findings/01057250/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: [Bell 407, 4 cases](https://openairdocs.org/ntsb-events/340/sequence.md?model=1182206), [All aircraft, 820 cases](https://openairdocs.org/ntsb-events/340/sequence.md) - [Enroute: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342); cases with it: [Bell 407, 4 cases](https://openairdocs.org/ntsb-events/342/sequence.md?model=1182206), [All aircraft, 1,858 cases](https://openairdocs.org/ntsb-events/342/sequence.md) - [Emergency descent: Off-field or emergency landing](https://openairdocs.org/ntsb-events/440); cases with it: [Bell 407, 8 cases](https://openairdocs.org/ntsb-events/440/sequence.md?model=1182206), [All aircraft, 3,365 cases](https://openairdocs.org/ntsb-events/440/sequence.md) - [Landing-flare/touchdown: Hard landing](https://openairdocs.org/ntsb-events/092); cases with it: [Bell 407, 13 cases](https://openairdocs.org/ntsb-events/092/sequence.md?model=1182206), [All aircraft, 2,102 cases](https://openairdocs.org/ntsb-events/092/sequence.md) ## Analysis The pilot reported that, shortly after departure, the helicopter yawed left and that he heard a "loud howling/grinding sound" emanating from the upper area of the helicopter. He subsequently reduced power and performed a minimum power descent to an open area. During the landing, the helicopter touched down hard. A postimpact examination of the engine found that two third-stage turbine wheel blades had cracked and separated due to high-cycle fatigue at the trailing edge during operation of one or more natural frequencies of the wheel. Four additional blades displayed fatigue cracks. Metallurgy examinations revealed that the blades had no evidence of material anomalies and met the material hardness and composition specifications. The observed high-cycle fatigue initiation and propagation characteristics were consistent with operating in a condition conducive to vibration. The engine manufacturer plans to release design changes that will increase the operating speed natural frequency margin and improve the vibration margin. ## Factual narrative On April 14, 2012, approximately 0255 central daylight time, a Bell 407 helicopter, N509MT, sustained substantial damage during a forced landing near Aberdeen, South Dakota. The commercial pilot, the sole occupant, sustained minor injuries. The helicopter was registered to and operated by Med-Trans Corp, Tucson, Arizona under the provisions of 14 Code of Federal Regulations Part 91 as a positioning flight. Visual meteorological conditions prevailed for the flight. The flight originated from the Aberdeen Regional Airport (KABR), Aberdeen, South Dakota, about 0250.According to a statement provided by the pilot, shortly after departing KABR, the helicopter began a left yaw and emanated a loud howling/grinding sound from the upper area of the helicopter. Suspecting a failed or impending failure of the main drive shaft or transmission, the pilot reduced power and scanned for any caution lights. With no caution light illuminated, the pilot began a minimum power descent to an open area. During the landing, the helicopter touched down hard resulting in spread skids, a severed tailboom, and damage to the main rotor blades. The pilot egressed the helicopter and notified with communication center of the accident at 0258. An eyewitness reported that he heard a helicopter departing the airport and the engine did not sound normal. The engine made a noise similar to a back fire and he saw sparks and flames coming out of the exhaust. He could see flames from the helicopter as it descended. A postaccident examination of the helicopter found internal damage to the engine. The engine was removed and transported to Rolls-Royce for an examination. On May 16, 2012, an engine exam was conducted under the auspices of the Federal Aviation Administration. The examination revealed that two blades from the third stage turbine wheel had fatigue cracked and separated. One other blade also display signatures of fatigue cracks. Metallurgy confirmed that the blades had no evidence of material anomalies, and met the proper values for material hardness and composition. Rolls-Royce engineering has determined that the third stage turbine wheel blades fractured in high cycle fatigue at the trailing edge location due to operation on one or more natural frequencies of the wheel. The observed high cycle fatigue initiation and propagation characteristics are consistent with operating in a condition that is conducive to vibration. Rolls-Royce plans to release two design changes that will increase the operating speed natural frequency margin on the initial change and further increase the frequency margin and also improve the vibration margin on the second design change. ## Aircraft - Registration: [N509MT](https://openairdocs.org/deregistered/N509MT-2012-07-30), registration cancelled 2012-07-30, S/N 53281, built 1998 (OpenAirDocs) - Reported make and model: BELL 407 - Registry model: [Bell 407](https://openairdocs.org/model/bell-407) (registry code 1182206) (OpenAirDocs) - Registry engine: [Allison 250-C47 series](https://openairdocs.org/engine/allison-250-c47-series) (registry code 03029, turbo-shaft) (OpenAirDocs) - Category: Helicopter - Serial number: 53281 - Airframe hours: 7379 - Engines: Rolls-Royce 250-C47B 650 horsepower turbo shaft - Damage: Substantial damage - Flight: Positioning, Part 91 - Operator: Med-Trans Corp - Registered owner: Med-Trans Corp - Airworthiness certificate: Standard, Normal - Last inspection: AAIP, March 26, 2012, 36 hours before - Departed: KABR, Aberdeen, SD - Destination: SD54, Aberdeen, SD - Flight plan: Company VFR ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 44; injuries: minor; commercial; airplane ratings: single-engine land; instrument ratings: helicopter, airplane; medical: class 2, with waivers/limitations; last flight review April 12, 2012; seat: right; flight hours: 3,790 total, 23 in this make and model, 2,150 as pilot in command, 9 in the last 90 days, 4 in the last 30 days, 2 in the last 24 hours ## Weather - Conditions: Visual (VMC), Night - Wind: 240° at 3 knots - Visibility: 5 statute miles - Lowest ceiling: none - Temperature: 37 °F, dew point 36 °F - Altimeter: 29.70 inHg - Observed at: KABR, 2 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 20120414010679A](https://openairdocs.org/incident/20120414010679A), Apr 14, 2012: Bell 407, Aberdeen, SD, Substantial damage. Accident occurred on 4-14-2012, about 0200 CDT (0700Z) near Aberdeen, SD. Pilot had just refueled at the Aberdeen (abr) airport and was ferrying the aircraft… ## Docket (6 files) The files NTSB released with the investigation on November 14, 2013, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=83384. 2.8 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 1.1 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40400357&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Redacted.PDF - Witness Statement (item 2, .PDF, 143 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40400355&FileExtension=.PDF&FileName=Witness%20Statement-Redacted.PDF - Photo 1: Wreckage overview (photo from Med-Trans) (item 3, .PDF, 187 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40400353&FileExtension=.PDF&FileName=Photo%201%3A%20Wreckage%20overview%20(photo%20from%20Med-Trans)-Master.PDF - Reports from Parties to the Investigation: Engine examination summary (item 4, .PDF, 103 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40400308&FileExtension=.PDF&FileName=Reports%20from%20Parties%20to%20the%20Investigation%3A%20Engine%20examination%20summary-Master.PDF - Statement of Party Representatives to NTSB Investigation (item 5, .PDF, 1.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40400351&FileExtension=.PDF&FileName=Statement%20of%20Party%20Representatives%20to%20NTSB%20Investigation-Redacted.PDF - Release of Aircraft Wreckage, NTSB Form 6120.15 (item 6, .PDF, 85 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40400354&FileExtension=.PDF&FileName=Release%20of%20Aircraft%20Wreckage,%20NTSB%20Form%206120.15-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.