# NTSB CEN13LA473: Air Tractor AT-502B, N6113C, Nauvoo, IL, July 15, 2013 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: July 15, 2013, 11:30 local (16:30 UTC) - Place: Nauvoo, IL - Coordinates: 40.549999, -91.383331 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=40.5500&lon=-91.3833&mi=10 - Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping) - Defining event: [Maneuvering-low-alt flying: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report December 15, 2014 - Report: Approved by Office Director - NTSB office: Central Region - Parties: Pratt & Whitney Canada, FAA -- Flight Standards - NTSB case key (mKey): 87713 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CEN13LA473 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/87713/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=87713 - Page: https://openairdocs.org/ntsb/CEN13LA473 ## Probable cause A fatigue failure of an engine compressor turbine blade, which resulted in extensive secondary engine damage and a complete loss of engine power. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Engine (turbine/turboprop): compressor section](https://openairdocs.org/ntsb-findings/01057230): Aircraft › Aircraft power plant · Failure (probable cause); cases with it: [Air Tractor AT-502B, 1 case](https://openairdocs.org/ntsb-findings/01057230/cases.md?model=0390307), [All aircraft, 53 cases](https://openairdocs.org/ntsb-findings/01057230/cases.md) - [Engine (turbine/turboprop): compressor section](https://openairdocs.org/ntsb-findings/01057230): Aircraft › Aircraft power plant · Fatigue/wear/corrosion (probable cause); cases with it: [Air Tractor AT-502B, 1 case](https://openairdocs.org/ntsb-findings/01057230/cases.md?model=0390307), [All aircraft, 53 cases](https://openairdocs.org/ntsb-findings/01057230/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Maneuvering-low-alt flying: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) (defining event); cases with it: [Air Tractor AT-502B, 8 cases](https://openairdocs.org/ntsb-events/341/sequence.md?model=0390307), [All aircraft, 3,820 cases](https://openairdocs.org/ntsb-events/341/sequence.md) - [Emergency descent: Off-field or emergency landing](https://openairdocs.org/ntsb-events/440); cases with it: [Air Tractor AT-502B, 14 cases](https://openairdocs.org/ntsb-events/440/sequence.md?model=0390307), [All aircraft, 3,365 cases](https://openairdocs.org/ntsb-events/440/sequence.md) - [Landing: Collision with terr/obj (non-CFIT) ](https://openairdocs.org/ntsb-events/470); cases with it: [Air Tractor AT-502B, 46 cases](https://openairdocs.org/ntsb-events/470/sequence.md?model=0390307), [All aircraft, 10,189 cases](https://openairdocs.org/ntsb-events/470/sequence.md) ## Analysis The pilot reported that, as he was setting up for the initial aerial application run, he heard a "loud explosion," at which point, the propeller stopped turning. Metallic debris emitted from the engine exhaust, which was followed by grinding noises coming from the engine. The pilot executed a forced landing to a soybean field, which resulted in the right main landing gear collapsing and the right wing sustaining substantial damage. A postaccident engine examination revealed that one compressor turbine blade separated from the disc as a result of fatigue. The remaining engine damage was due to the secondary impact of blade fragments during the failure sequence. Further examination of the initial compressor blade fracture surface was limited by the secondary damage sustained during the event. ## Factual narrative On July 15, 2013, about 1130 central daylight time, an Air Tractor AT-502B airplane, N6113C, was substantially damaged during a forced landing following a loss of engine power near Nauvoo, Illinois. The pilot was not injured. The airplane was registered to and operated by Air Advantage Inc. under the provisions of 14 Code of Federal Regulations Part 137 as an aerial application flight. Visual meteorological conditions prevailed for the flight, which was not operated on a flight plan. The local flight originated from Schilson Field Airport (IS51), Carthage, Illinois, about 1125.The pilot reported that after takeoff he proceeded 5 miles north toward the assigned agricultural field. As he was setting up for the initial spray run, he heard a "loud explosion" at which point the propeller stopped turning. He noted that metallic debris was emitted from the engine exhaust, which was followed by grinding noises from the engine. He executed a forced landing to a soybean field; however, the airplane overran the bean field and crossed into a corn field, at which time the right main landing gear collapsed. The airplane came to rest upright, with substantial damage to the right wing. A postaccident engine examination revealed damage to the compressor turbine disc, power turbine disc, and the compressor turbine and power turbine guide vane rings and shrouds. Metallurgical examination determined that one compressor turbine blade exhibited features consistent with fatigue failure initiating at the trailing edge of the blade section, near the root. A majority of the fracture surface was obscured by corrosion products and metal splatter, which precluded a complete evaluation of the fracture surface. Metallographic examination of the trailing edge of the blade fracture surface revealed no material anomalies. The blade material and airfoil trailing edge thickness were determined to be within drawing requirements. The remaining blades of the compressor turbine displayed gouges and fracture surfaces consistent with secondary impact damage and overstress failures. The power turbine blades were separated from the root to about two-thirds of the blade span. The fracture features were consistent with overstress separations of the blade sections. Five blades were not separated; these blades exhibited gouges consistent with secondary impact damage from the liberated blades. Scraping damage was observed on the compressor and turbine shrouds, which was consistent with blade contact during the engine failure sequence after the initial compressor blade failure. The airplane was powered by a 750-shaft horsepower Pratt & Whitney Canada PT6A-34AG engine. At the time of the accident, the engine had accumulated about 9,961 hours since new, with about 7,336 hours since overhaul. The most recent recorded engine maintenance consisted of a 100-hour inspection completed on July 6, 2013, at 9,950 hours total time. The most recent engine hot section inspection was completed on December 31,2012, at 9,782 hours total time. Maintenance records indicated that the engine was removed and inspected due to excessive vibration in April 2008 at 7,132 hours engine total time. Damage to the power and compressor turbine blades and guide vane rings was observed. Overhauled power turbine blades and an overhauled power turbine guide vane ring were installed. New compressor turbine blades were installed at that time. The most recent engine overhaul was completed in April 2000 at 2,625 hours total time since new. Based on the available engine maintenance records, the most recent review of engine start cycles was completed on December 22, 2012. At that time, the engine had accumulated 9,752 hours total time, with 5,634 engine start cycles consumed. The compressor turbine start cycle limit was 16,000. ## Aircraft - Registration: [N6113C](https://openairdocs.org/deregistered/N6113C-2022-11-05), registration cancelled 2022-11-05, S/N 502B-0275, built 1994 (OpenAirDocs) - Reported make and model: AIR TRACTOR INC AT-502B - Registry model: [Air Tractor AT-502B](https://openairdocs.org/model/air-tractor-at-502b) (registry code 0390307) (OpenAirDocs) - Registry engine: [Pratt & Whitney PT6A series](https://openairdocs.org/engine/pratt-whitney-pt6a-series) (registry code 52034, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 502B-0275 - Airframe hours: 9961 - Engines: P&W PT6A-34AG 750 horsepower turbo prop - Damage: Substantial damage - Flight: Aerial application, Part 137 - Operator: Air Advantage Inc. - Registered owner: Air Advantage Inc. - Airworthiness certificate: Special, Restricted (Special) - Last inspection: 100 hour, July 6, 2013, 11 hours before - Departed: IS51, Carthage, IL - Destination: IS51, Carthage, IL ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 50; injuries: none; commercial; airplane ratings: single-engine land; medical: class 2, with waivers/limitations; last flight review September 10, 2011; seat: single; flight hours: 19,976 total, 3,500 in this make and model, 19,976 as pilot in command, 350 in the last 90 days, 250 in the last 30 days, 8 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 160° at 3 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 84 °F, dew point 73 °F - Altimeter: 30.25 inHg - Observed at: FSW, 7 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 20130715013539A](https://openairdocs.org/incident/20130715013539A), Jul 15, 2013: Air Tractor Inc AT-502B, Nauvoo, IL, Substantial damage. Aircraft was being flown from one field to another and the engine failed. The aircraft landed in a field sustaining substantial damage. ## Other investigations on N6113C (1) 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. - [NTSB CEN19FA259](https://openairdocs.org/ntsb/CEN19FA259), Aug 8, 2019: Air Tractor AT502 (N6113C), Sumner, IA, destroyed, 1 fatal. Probable cause: The pilot’s impairment by medical conditions and/or medications, which resulted in the airplane’s impact with power lines and terrain. ## Docket (3 files) The files NTSB released with the investigation on November 12, 2014, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=87713. 2.9 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 399 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40400908&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Redacted.PDF - Engine Maintenance Logbook (item 2, .PDF, 2.4 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40406190&FileExtension=.PDF&FileName=Engine%20Maintenance%20Logbook-Redacted.PDF - Summary of Metallurgy Examination (item 3, .PDF, 62 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40418899&FileExtension=.PDF&FileName=Summary%20of%20Metallurgy%20Examination-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.