# NTSB WPR11LA386: Air Tractor AT-401, N1012T, Hardin, MT, August 16, 2011 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: August 16, 2011, 09:00 local (15:00 UTC) - Place: Hardin, MT - Coordinates: 45.733333, -107.616668 - Nearby events: https://openairdocs.org/map.md?lat=45.7333&lon=-107.6167&mi=10 - Phase of flight: [Takeoff](https://openairdocs.org/ntsb-phases/300) (OpenAirDocs' grouping) - Defining event: [Takeoff: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report January 12, 2015 - Report: Approved by Office Director - NTSB office: Western Pacific Region - Parties: FAA FSDO - NTSB case key (mKey): 81510 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR11LA386 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/81510/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=81510 - Page: https://openairdocs.org/ntsb/WPR11LA386 ## Probable cause The loss of engine power during takeoff due to the fatigue failure of the turbine wheel blades, which resulted from inadequate maintenance and inspections. ## 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: [Air Tractor AT-401, 1 case](https://openairdocs.org/ntsb-findings/01057250/cases.md?model=0390204), [All aircraft, 74 cases](https://openairdocs.org/ntsb-findings/01057250/cases.md) - [Engine (turbine/turboprop)](https://openairdocs.org/ntsb-findings/01057200): Aircraft › Aircraft power plant · Not serviced/maintained (probable cause); cases with it: [Air Tractor AT-401, 2 cases](https://openairdocs.org/ntsb-findings/01057200/cases.md?model=0390204), [All aircraft, 67 cases](https://openairdocs.org/ntsb-findings/01057200/cases.md) - [Engine (turbine/turboprop)](https://openairdocs.org/ntsb-findings/01057200): Aircraft › Aircraft power plant · Inadequate inspection (probable cause); cases with it: [Air Tractor AT-401, 2 cases](https://openairdocs.org/ntsb-findings/01057200/cases.md?model=0390204), [All aircraft, 67 cases](https://openairdocs.org/ntsb-findings/01057200/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Takeoff: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342) (defining event); cases with it: [Air Tractor AT-401, 4 cases](https://openairdocs.org/ntsb-events/342/sequence.md?model=0390204), [All aircraft, 1,858 cases](https://openairdocs.org/ntsb-events/342/sequence.md) - [Emergency descent: Collision with terr/obj (non-CFIT) ](https://openairdocs.org/ntsb-events/470); cases with it: [Air Tractor AT-401, 10 cases](https://openairdocs.org/ntsb-events/470/sequence.md?model=0390204), [All aircraft, 10,189 cases](https://openairdocs.org/ntsb-events/470/sequence.md) ## Analysis The pilot reported that, shortly after takeoff for the aerial application flight, the engine quit. He did not have sufficient altitude to restart the engine, so he made a forced landing to an open field; the airplane came to rest upright, and the airframe sustained structural damage. A visual examination of the engine at the accident site revealed that the compressor section had sustained fire damage and that the turbine section had broken and missing vanes. Postaccident metallurgical examination revealed that one of the turbine wheel blades had fractured and that the fracture surfaces revealed signatures consistent with fatigue propagation and subsequent failure. About 1 year 5 months before the accident, an examination of the engine revealed excessive wear to the combustor outer liner lugs, and the engine was determined to be unserviceable. About 1 year 1 month later (about 4 months before the accident), the airplane underwent a 100-hour inspection and was returned to service in an airworthy condition. No evidence was found indicating that the engine was overhauled or replaced during the 1-year period between when it was determined to be unserviceable and when it was returned to service. The pilot reported that the airplane had undergone a 100-hour inspection 1 week before the accident, but no entries were found pertaining to the inspection in the airplane's maintenance logbooks. The engine had accrued 2,819.6 hours since major overhaul. No evidence was found indicating that the engine was inspected in accordance with the manufacturer's recommended time between overhaul inspection interval of 2,000 hours. It is likely that proper maintenance inspections would have detected the crack and wear in the engine. ## Factual narrative HISTORY OF FLIGHT On August 16, 2011, about 0900 mountain daylight time, an Air Tractor AT-401 airplane, N1012T, was substantially damaged during a forced landing near Hardin, Montana. The owner/pilot operated the airplane under the provisions of 14 Code of Federal Regulations Part 137 as an aerial application flight. The commercial pilot, the sole occupant, was not injured. Visual meteorological conditions prevailed, and no flight plan was filed. According to the pilot, he had just taken off and was maneuvering the airplane to start an application pass when the engine quit. During the forced landing to the field, the airplane came to rest upright and sustained structural damage to the entire airplane. A Federal Aviation Administration (FAA) inspector responded to the accident site and reported that the debris field consisted of fire damaged hay fields about 1 mile behind the main wreckage. A visual inspection of the engine revealed that the compressor section had sustained fire damage, and the turbine section had broken and missing vanes. AIRCRAFT INFORMATION According to the engine logbook, on April 4, 2002, the accident engine was installed on the accident airplane, with zero time since overhaul. The engine was started and test flown with no discrepancies. In March 2010, a GE aviation field support manager, and a technician from Premier Turbine in Neosho, Missouri, performed a borescope inspection of the engine in accordance with combustor outer liner lugs Service Bulletin. At that time they noted that the combustor outer liner lugs were 85-90 percent worn, which rendered the engine unserviceable. They passed on the information to the operator and recommended an engine overhaul due to the condition of the engine hot section and high time since overhaul. On April 19, 2011, the airplane had undergone a 100-hour inspection and was returned to service in an airworthy condition; no evidence was found indicating that the engine had been worked on or replaced during the 1-year period between when it was deemed unserviceable and when it was returned to service. According to the pilot, the airplane had undergone a 100-hour inspection a week prior to the accident; however, there was no corresponding airframe or engine logbook entry. Recorded time since major overhaul was 2,819.6 hours. According to the engine manufacturer, the engine had three inspection times that were required to be adhered to: 1. Time between Overhaul (TBO) – 2,000 engine flight hours 2. Cycles between Overhaul – 2,250 engine flight cycles 3. Calendar time – Five years TEST AND RESEARCH The turbine section assembly and exhaust housing, turbine wheel and blades, and compressor assembly with shaft were shipped to the National Transportation Safety Board's (NTSB) Materials Laboratory in Washington, D.C., for further examination. The materials lab specialist reported that the majority of the first stage turbine wheel blades were missing the bulk of the airfoil material above theplatforms. One blade, at the 12 o-clock position had fractured below the airfoil platform, with a blade fragment retained in the wheel slot. This area exhibited features consistent with a fatigue crack that initiated at the forward left side of the blade fir tree. The specialist reported a flat faceted feature that was consistent with stage 1 fatigue crack growth typical after fatigue crack initiation in nickel-based superalloys, was located at the crack initiation site. Ratchet marks observed in this area were also consistent with fatigue crack propagation from the crack initiation site. A detailed examination report is attached to the docket for this accident. ## Aircraft - Registration: [N1012T](https://openairdocs.org/aircraft/N1012T), registered now, S/N 401-0719 (OpenAirDocs) - Reported make and model: AIR TRACTOR INC AT-401 - Registry model: [Air Tractor AT-401](https://openairdocs.org/model/air-tractor-at-401) (registry code 0390204) (OpenAirDocs) - Registry engine: [Pratt & Whitney R1340 series](https://openairdocs.org/engine/pratt-whitney-r1340-series) (registry code 52016, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 401-0719 - Airframe hours: 7300 - Engines: GE Aviation Czech M601E-11 751 horsepower turbo prop - Damage: Substantial damage - Flight: Aerial application, Part 137 - Airworthiness certificate: Special, Restricted (Special) - Last inspection: Annual, April 19, 2011, 295.4 hours before - Departed: Hardin, MT - Destination: Hardin, MT ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 54; injuries: none; commercial; airplane ratings: single-engine land; medical: class 2, without waivers/limitations; seat: single; flight hours: 15,600 total, 5,000 in this make and model ## Weather - Conditions: Visual (VMC), Day - Wind: calm - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 61 °F, dew point 52 °F - Altimeter: 30.17 inHg - Observed at: BIL, 39 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 20110816018769A](https://openairdocs.org/incident/20110816018769A), Aug 16, 2011: Air Tractor Inc AT-401, Hardin, MT, Substantial damage. Turbine engine failed shortly after take off. Pilot made an emergency landing,the aircraft right wing caught in the crop and caused the aircraft to nose into… ## Docket (6 files) The files NTSB released with the investigation on November 19, 2014, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=81510. 8.7 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 873 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40376175&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Redacted.PDF - Materials Laboratory Factual Report (item 2, .PDF, 5.9 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40419197&FileExtension=.PDF&FileName=Materials%20Laboratory%20Factual%20Report-Master.PDF - FAA Inspector Statement (item 3, .PDF, 345 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40419200&FileExtension=.PDF&FileName=FAA%20Inspector%20Statement-Redacted.PDF - Aircraft Logbook Excerpt (item 4, .PDF, 725 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40419201&FileExtension=.PDF&FileName=Aircraft%20Logbook%20Excerpt-Redacted.PDF - Engine Logbook Excerpt (item 5, .PDF, 667 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40419202&FileExtension=.PDF&FileName=Engine%20Logbook%20Excerpt-Redacted.PDF - Revised Factual Report (item 6, .PDF, 104 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40420334&FileExtension=.PDF&FileName=Revised%20Factual%20Report-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.