# NTSB CEN15LA239: Ayres S2R G6, N3300U, Tivoli, TX, May 20, 2015 - Type: NTSB accident investigation - Classification: Accident · Minor injuries · Limited investigation · Final report - Date: May 20, 2015, 14:40 local (19:40 UTC) - Place: Tivoli, TX - Coordinates: 28.392221, -96.893333 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=28.3922&lon=-96.8933&mi=10 - Phase of flight: [Landing](https://openairdocs.org/ntsb-phases/550) (OpenAirDocs' grouping) - Defining event: [Landing: Nose over/nose down](https://openairdocs.org/ntsb-events/096) - Highest injury: Minor injuries - Injuries: 1 minor - Status: Completed, report November 19, 2015 - Report: Approved by Office Director - NTSB office: Central Region - Parties: FAA, Woodward Inc, Honeywell Aerospace - ADs cited in the narratives: [AD 2006-15-08](https://openairdocs.org/ad/2006-15-08) (OpenAirDocs) - NTSB case key (mKey): 91209 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CEN15LA239 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/91209/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=91209 - Page: https://openairdocs.org/ntsb/CEN15LA239 ## Probable cause The failure of the fuel control unit due to the worn stub shaft spline, which resulted in an engine overspeed. Contributing to the accident was maintenance personnel's inadequate inspection of the fuel control unit. ## 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 · Fatigue/wear/corrosion (probable cause); cases with it: [Ayres S2R-G6, 2 cases](https://openairdocs.org/ntsb-findings/01057320/cases.md?model=0970216), [All aircraft, 59 cases](https://openairdocs.org/ntsb-findings/01057320/cases.md) - [Engine fuel and control: fuel controlling system](https://openairdocs.org/ntsb-findings/01057320): Aircraft › Aircraft power plant · Inadequate inspection (probable cause); cases with it: [Ayres S2R-G6, 2 cases](https://openairdocs.org/ntsb-findings/01057320/cases.md?model=0970216), [All aircraft, 59 cases](https://openairdocs.org/ntsb-findings/01057320/cases.md) - [Maintenance: scheduled/routine maintenance](https://openairdocs.org/ntsb-findings/02062010): Personnel issues › Task performance · Maintenance personnel (probable cause); cases with it: [Ayres S2R-G6, 1 case](https://openairdocs.org/ntsb-findings/02062010/cases.md?model=0970216), [All aircraft, 320 cases](https://openairdocs.org/ntsb-findings/02062010/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); cases with it: [Ayres S2R-G6, 4 cases](https://openairdocs.org/ntsb-events/340/sequence.md?model=0970216), [All aircraft, 820 cases](https://openairdocs.org/ntsb-events/340/sequence.md) - [Landing: Nose over/nose down](https://openairdocs.org/ntsb-events/096) (defining event); cases with it: [Ayres S2R-G6, 1 case](https://openairdocs.org/ntsb-events/096/sequence.md?model=0970216), [All aircraft, 2,287 cases](https://openairdocs.org/ntsb-events/096/sequence.md) ## Analysis The pilot reported that, during the accident flight, which was the twelfth aerial application flight of the day, the engine made an uncommanded power acceleration. The pilot retarded the throttle lever, but the engine did not respond. The pilot subsequently made a forced landing into a field, and the airplane nosed over and then came to rest inverted. A postaccident examination of the airplane revealed no anomalies with the engine rigging. Examination of the fuel control unit revealed that the stub shaft spline was worn beyond the allowable limits. Such wear can allow the fuel control underspeed governor to be driven at a lower speed than the engine speed, which can increase fuel flow and engine speed and is consistent with the uncommanded power acceleration that occurred during the accident flight. A review of the airplane's maintenance records revealed that, 2 months before the accident flight, the fuel control unit was inspected for wear and damage in accordance with an airworthiness directive (AD). It is unlikely that the wear observed during the postaccident examination could have occurred between the time of the AD inspection and the accident. It is likely that the AD was either not accomplished as noted in the maintenance records or that maintenance personnel inadequately conducted the inspection. ## Factual narrative On May 20, 2015, about 1440 central daylight time, an Ayres Corporation S2R-G6 agricultural airplane, N3300U, made a forced landing into a field following a loss of engine power near Tivoli, Texas. The commercial pilot, who was the sole occupant, sustained minor injuries and the airplane was substantially damage. The airplane was registered to AT Rental Properties and operated by AT Ag Services, LLC, Tivoli, Texas, under the provisions of 14 Code of Federal Regulations Part 137 as an aerial application flight. Visual meteorological conditions prevailed at the time of the accident and no flight plan was filed. The local flight originated from a private strip near Tivoli, Texas. The pilot reported that the accident flight was the twelfth aerial application flight of the day. He was carrying a load of fertilizer to the destination field when the engine made an uncommanded power acceleration. He noticed the engine temperature increase so he retarded the power lever, but the engine did not respond. The pilot jettisoned the load of fertilizer and shut off the fuel supply to the engine. He then made a forced landing into a field; during the landing the airplane nosed over and came to rest inverted. A postaccident examination of the airplane was conducted by the responding Federal Aviation Administration (FAA) inspector and a representative from Honeywell Aerospace. The examination revealed no anomalies with the engine rigging, but the engine's fuel control unit stub shaft spline appeared to be worn. No other anomalies were noted. On June 9, 2015, the fuel control unit was examined by Woodward, Inc., Loves Park, Illinois, with representatives from the NTSB, FAA, and Honeywell Aerospace. The examination revealed that the stub shaft spline was worn beyond the allowable limits. The internal spline was also checked using a specific go/no-go gauge, which should not fit between the teeth of the spline; the gauge rotated freely. This wear can allow the fuel control underspeed governor to be driven at a speed which is lower than the engine speed and subsequently increase fuel flow and engine speed. On August 24, 2006, the FAA issued Airworthiness Directive (AD) 2006-15-08, for Honeywell TPE331 series turboprop engines. The AD stated in part, "The AD results from reports of loss of the fuel control drive, leading to engine overspeed, overtorque, overtemperature, uncontained rotor failure, and asymmetric thrust in multi-engine airplanes. We are issuing this AD to prevent destructive overspeed that could result in uncontained rotor failure, and damage to the airplane." The AD specifies that Honeywell Service Bulletin (SB) TPE331-A73-0262 be used to accomplish the maintenance work. An excerpt from the SB: Initial Inspection of Engines with Affected FCU Assemblies (f) At the next scheduled inspection of the fuel control drive, but within 1,000 hours-in-service after the effective date of this AD: (1) Perform an initial dimensional inspection of the fuel controldrive for wear or damage. Information on spline inspection can be found in Section 72-00-00 of the applicable maintenance manuals. (2) Repair or replace the fuel pump, if the spline fails the dimensional inspection, with any serviceable fuel pump. (3) Repair or replace the FCU assembly, if the splines fail the dimensional inspection, with a serviceable modified FCU assembly. Repetitive Inspections of Engines with Affected FCU Assemblies (g) Thereafter, within 1,000 hours since-last-inspection: (1) Perform repetitive dimensional inspections of the fuel control drive, for wear or damage. Information on spline inspection can be found in Section 72-00-00 of the applicable maintenance manuals. (2) Repair or replace the fuel pump, if the spline fails the dimensional inspection, with any serviceable fuel pump. (3) Repair or replace the FCU assembly if the splines fail the dimensional inspection, with a serviceable modified FCU assembly. A review of the aircraft maintenance records revealed that AD 2006-15-08 was accomplished on March 16, 2015. The records noted that the AD inspection was to be completed again in 1,000 hours. ## Aircraft - Registration: [N3300U](https://openairdocs.org/aircraft/N3300U), registered now, S/N G6-139 (OpenAirDocs) - Reported make and model: AYRES CORPORATION S2R G6 - Registry model: [Ayres S2R-G6](https://openairdocs.org/model/ayres-s2r-g6) (registry code 0970216) (OpenAirDocs) - Registry engine: [AiResearch TPE331-5&6SER](https://openairdocs.org/engine/airesearch-tpe331-5-6ser) (registry code 01515, turbo-prop) (OpenAirDocs) - Category: Airplane - Serial number: G6-139 - Year built: 1996 - Engines: AiResearch TPE 331-10 turbo prop - Damage: Substantial damage - Flight: Aerial application, Part 137 - Operator: A T Ag Services, LLC - Registered owner: A T Rental Properties LLC - Airworthiness certificate: Special, Restricted (Special) - Last inspection: Continuous airworthiness, March 16, 2015 - Departed: Tivoli, TX - Destination: Tivoli, TX ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 58; injuries: minor; commercial; airplane ratings: single-engine land; medical: class 2, with waivers/limitations; last flight review May 18, 2015; seat: single; restraint: 3-point; flight hours: 300 in the last 90 days ## Weather - Conditions: Visual (VMC), Day - Wind: 160° at 9 knots - Visibility: 10 statute miles - Lowest ceiling: 5,000 ft broken - Temperature: 84 °F, dew point 73 °F - Altimeter: 29.95 inHg - Observed at: KPKV, 17 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 20150520023629A](https://openairdocs.org/incident/20150520023629A), May 20, 2015: Ayres Corporation S2R-G6, Tivoli, TX, Substantial damage. During cruse flight the pilot experienced uncontrolled engine acceleration. Pilot noted that temperature started to climb towards the red; he then started to… ## Docket (7 files) The files NTSB released with the investigation on October 21, 2015, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=91209. 5.1 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 3.5 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40433000&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Master.PDF - Airworthiness Directive 2006-15-08 (item 2, .PDF, 164 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40433001&FileExtension=.PDF&FileName=Airworthiness%20Directive%202006-15-08-Master.PDF - Service Bulletin TPE331-A73-0262 (item 3, .PDF, 92 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40433002&FileExtension=.PDF&FileName=Service%20Bulletin%20TPE331-A73-0262-Master.PDF - Statement of Party Representatives to NTSB Investigation (item 4, .PDF, 495 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40433003&FileExtension=.PDF&FileName=Statement%20of%20Party%20Representatives%20to%20NTSB%20Investigation-Master.PDF - Release of Aircraft Wreckage, NTSB Form 6120.15 (item 5, .PDF, 134 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40433004&FileExtension=.PDF&FileName=Release%20of%20Aircraft%20Wreckage,%20NTSB%20Form%206120.15-Master.PDF - Photos (item 6, .PDF, 2 photos, 274 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40433005&FileExtension=.PDF&FileName=Photos-Master.PDF - Maintenance Records (item 7, .PDF, 457 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40433006&FileExtension=.PDF&FileName=Maintenance%20Records-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.