# NTSB CEN22LA312: Air Tractor AT-502B, N5850R, Decatur, IL, July 11, 2022 - Type: NTSB accident investigation - Classification: Accident · No injuries · Class 3 · Limited · Final report - Date: July 11, 2022, 06:30 local (11:30 UTC) - Place: Decatur, IL - Coordinates: 39.83, -88.85 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=39.8300&lon=-88.8500&mi=10 - Phase of flight: [Takeoff](https://openairdocs.org/ntsb-phases/300) (OpenAirDocs' grouping) - Defining event: [Takeoff: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Central Region - Parties: FAA, Transportation Safety Board of Canada - NTSB case key (mKey): 105448 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CEN22LA312 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/105448/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=105448 - Page: https://openairdocs.org/ntsb/CEN22LA312 ## Probable cause Fracture of the compressor turbine (CT) blades due to creep. ## 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 · Failure (probable cause); cases with it: [Air Tractor AT-502B, 2 cases](https://openairdocs.org/ntsb-findings/01057250/cases.md?model=0390307), [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. - [Takeoff: 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) ## Analysis During departure climbout for spray operations, the pilot heard a “pop” and observed white smoke trailing the airplane. The pilot made a forced landing, during which the airplane struck an airport perimeter fence that resulted in substantial damaged to both wings. Examination revealed that all compressor turbine (CT) rotor blades were fractured at varying spanwise locations. The power turbine (PT) rotor blades downstream of the CT blades exhibited impact damage and were fractured at varying spanwise locations. Metallurgical analysis of the CT blades revealed micro-voids were present along the material grain boundaries and rafting of the gamma prime which were indicative of creep. Metallurgical analysis of the CT blades revealed solutioning of the gamma prime which is consistent with exposure to temperature in excess of the engine operating limits. It was not determined if the exposure to elevated temperatures occurred before or during the event. ## Factual narrative On July 11, 2022, about 0630 central daylight time, an Air Tractor AT-502B, N5850R, was substantially damaged when it was involved in an accident at Decatur Airport (DEC), Decatur, Illinois. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 137 flight. During initial climb out from DEC, the pilot heard a “pop” and observed white smoke trailing the airplane. The pilot noticed a loss of power and lowered the nose to gain airspeed, and then made a forced landing into a bean field, during which the airplane struck an airport perimeter fence that substantially damaged both wings. Postaccident examination of the engine revealed that all CT rotor blades were fractured at varying spanwise locations. The PT rotor blades immediately downstream of the CT exhibited impact damage and were fractured at varying spanwise locations. Circumferential rub was observed on multiple components, most notably the PT vane ring, consistent with engine rotation at impact. The CT rotor blades were removed for materials analysis. A microstructure analysis of sampled blades identified alloy solutioning consistent with exposure to temperatures in excess of engine operating limits. A scanning electron microscope analysis of the CT rotor blades revealed micro-voids along the material grain boundaries, indicative of creep. Pratt & Whitney Canada service bulletin PT6A-72-1767 (revision 5) includes the following information regarding CT blade creep: There can be blade creep at the CT area when the engine is operated at higher temperatures and power than the Pilot Operating Handbook (POH) recommended power settings. To prevent creep-related events, introduce a new CT Disk Balancing Assembly which incorporates redesigned turbine blades made from a different material and increased gap at the blade inter and under platform. The new CT blade design features single-crystal material, which is comprised of a continuous crystal lattice that eliminates grain boundaries to improve creep resistance. The new CT blade was not intended to prevent blade creep if the engine is operated outside of the engine limitations. The service bulletin was not mandated by Transport Canada or the Federal Aviation Administration, so compliance was at the discretion of the owner/operator. ## Aircraft - Registration: [N5850R](https://openairdocs.org/deregistered/N5850R-2025-05-05), registration cancelled 2025-05-05, S/N 502B-0685, built 2004 (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 Canada PT6A-34AG](https://openairdocs.org/engine/pratt-whitney-canada-pt6a-34ag) (registry code 52251, turbo-prop) (OpenAirDocs) - Category: Airplane - Serial number: 502B-0685 - Year built: 2004 - Airframe hours: 5975 - Engines: Pratt & Whitney Canada PT6A-34AG 750 horsepower turbo prop - Damage: Substantial damage - Flight: Aerial application, Part 137 - Operator: Adams Aerial Solutions LLC - Registered owner: Adams Aerial Solutions LLC - Airworthiness certificate: Special, Restricted (Special) - Last inspection: Annual, November 16, 2021, 51 hours before - Departed: DEC, Decatur, IL - Destination: DEC, Decatur, IL - Airport: DEC, Decatur Airport, runway 6, 8,496 × 150 ft, asphalt - Equipment: Stall warning system, ADS-B, Data recorder, Heads up display ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 23; injuries: none; private, commercial; airplane ratings: single-engine land; medical: class 2, with waivers/limitations; last flight review January 14, 2021; seat: single; restraint: 5-point; flight hours: 760 total, 112 in this make and model, 684 as pilot in command, 37 in the last 90 days, 30 in the last 30 days, 10 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 210° at 8 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 70 °F, dew point 61 °F - Altimeter: 29.90 inHg - Observed at: KDEC, 1 nm away - METAR: KDEC 111154Z 21008KT 10SM CLR 21/16 A2990 RMK AO2 SLP119 T02060156 10206 20183 58011 ## 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 20220711008399A](https://openairdocs.org/incident/20220711008399A), Jul 11, 2022: Air Tractor Inc AT-502B, Decatur, IL, Substantial damage. Narrative: NORMAL TAKEOFF FROM RUNwAY 06 AT DECATUR ILLINOIS (KDEC) TO THE NORTHEAST APROXIMATELY 0630 LOCAL TIME ON 07/11/2022 WITH A PLAN TO SPRAY A… ## Docket (6 files) The files NTSB released with the investigation on February 21, 2024, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=105448. 12.8 MB in all. - Pilot/operator aircraft accident report, NTSB form 6120.1 (item 1, PDF, 11 pages, 6.5 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16335135&FileExtension=pdf&FileName=6120_Redacted-Rel.pdf - Photos of airplane at accident site (item 2, PDF, 2 pages, 164 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16333274&FileExtension=pdf&FileName=Photos-Rel.pdf - Powerplants group chair's factual report (item 3, PDF, 23 pages, 4.5 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16274503&FileExtension=pdf&FileName=CEN22LA312-%20Powerplants%20Group%20Chair%27s%20Factual%20Report_Redacted-Rel.pdf - Powerplants attachment 1- pwc service investigation accident/incident report no. 23ECN00007, engine accessories investigation (item 4, PDF, 9 pages, 650 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16274513&FileExtension=pdf&FileName=Powerplants%20Attachment%201,%20Engine%20Accessories%20Report-Rel.pdf - Powerplants attachment 2- pwc service investigation accident/incident report no. 22-118, materials laboratory analysis (item 5, PDF, 7 pages, 544 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16275360&FileExtension=pdf&FileName=Powerplants%20Attachment%202,%20Materials%20Laboratory%20Analysis%20Report-Rel.pdf - Release of aircraft wreckage, NTSB form 6120.15 (item 6, PDF, 1 page, 534 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16428735&FileExtension=pdf&FileName=wreckage%20release_Redacted-Rel.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.