# NTSB ERA17LA326: Air Tractor AT 502, N4531K, Union City, TN, September 15, 2017 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: September 15, 2017, 09:15 local (14:15 UTC) - Place: Union City, TN - Coordinates: 36.392776, -89.116668 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=36.3928&lon=-89.1167&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Defining event: [Enroute-cruise: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report August 10, 2020 - Report: Approved by Office Director - NTSB office: Eastern Region Aviation - Parties: FAA/FSDO, Pratt and Whitney - NTSB case key (mKey): 96017 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ERA17LA326 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/96017/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=96017 - Page: https://openairdocs.org/ntsb/ERA17LA326 ## Probable cause The catastrophic failure of the compressor turbine blades, which resulted in a total loss of engine power. Contributing to the accident was the installation of undocumented, time-limited engine components of indeterminate age. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Engine (turbine/turboprop)](https://openairdocs.org/ntsb-findings/01057200): Aircraft › Aircraft power plant · Failure (probable cause); cases with it: [Air Tractor AT-502, 2 cases](https://openairdocs.org/ntsb-findings/01057200/cases.md?model=0390303), [All aircraft, 67 cases](https://openairdocs.org/ntsb-findings/01057200/cases.md) - [Power plant](https://openairdocs.org/ntsb-findings/01057100): Aircraft › Aircraft power plant · Incorrect service/maintenance (probable cause); cases with it: [Air Tractor AT-502, 1 case](https://openairdocs.org/ntsb-findings/01057100/cases.md?model=0390303), [All aircraft, 198 cases](https://openairdocs.org/ntsb-findings/01057100/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Enroute-cruise: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) (defining event); cases with it: [Air Tractor AT-502, 4 cases](https://openairdocs.org/ntsb-events/341/sequence.md?model=0390303), [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-502, 7 cases](https://openairdocs.org/ntsb-events/440/sequence.md?model=0390303), [All aircraft, 3,365 cases](https://openairdocs.org/ntsb-events/440/sequence.md) - [Landing: Part(s) separation from AC](https://openairdocs.org/ntsb-events/338); cases with it: [Air Tractor AT-502, 1 case](https://openairdocs.org/ntsb-events/338/sequence.md?model=0390303), [All aircraft, 563 cases](https://openairdocs.org/ntsb-events/338/sequence.md) ## Analysis The pilot of the aerial application flight indicated that the airplane was in cruise flight on its way to an application site when he heard a "pop," and the engine lost total power. The pilot maneuvered the airplane for a forced landing on a roadway but changed his forced landing site to a corn field due to vehicle traffic. After touchdown, the main landing gear separated, which resulted in substantial damage to the fuselage. Examination of the engine revealed catastrophic internal damage; all compressor turbine blades were fractured. Metallurgical examination revealed fracture features consistent with high-velocity impact and high-temperature deformation such as "creep." The primary fracture could not be identified; therefore, the sequence in which the fractures occurred could not be determined. The engine was an assembled compilation of manufacturer and aftermarket parts manufacturer approval (PMA) parts. Some PMA parts installed were not authorized for the application, and the serial numbers reflected in the maintenance records did not match the components installed. For example, the factory original compressor turbine disk was installed, but the logbook indicated another disk was installed. The compressor turbine disk was a time-limited item, and the total hours on the installed disk could not be verified. ## Factual narrative On September 15, 2017, about 0915 central daylight time, an Air Tractor AT-502, N4531K, was substantially damaged during collision with terrain following a forced landing after a total loss of engine power while in cruise flight near Union City, Tennessee. The commercial pilot was not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the aerial application flight which was conducted under the provisions of 14 Code of Federal Regulations Part 137.In an interview with a Federal Aviation Administration (FAA) inspector, the pilot reported he was in cruise flight on his way to an application site when he heard a 'pop' and the engine stopped producing power. The pilot maneuvered the airplane for a forced landing on a roadway but had to amend his forced landing site to a cornfield adjacent to the road due to vehicle traffic. After touchdown, the main landing gear separated which resulted in substantial damage to the fuselage. At 0915, the weather recorded at Everett-Stewart Regional Airport (UCY), about 6 miles east of the accident site, included clear skies and wind from 160° at 4 knots. The temperature was 23°C, and the dew point was 20°C. The altimeter setting was 30.06 inches of mercury. The pilot held a commercial pilot certificate with a rating for airplane single-engine land. The pilot reported 18,000 total hours of flight experience, of which 3,034 hours were in the accident airplane make and model. According to FAA records, the airplane was manufactured in 1990 and had accrued 5,490 total aircraft hours. The engine had two data plates and had been changed from a PWC PT6A-15AG engine to a PWC PT6A-34 engine under an FAA supplemental type certificate (STC). A Pratt & Whitney Canada (PWC) accident investigator performed a field examination of the accident airplane's engine under the supervision of an FAA aviation safety inspector. The examination revealed catastrophic internal damage, and parts of the compressor turbine wheel with blade fragments were harvested and forwarded to the NTSB Materials Laboratory for examination. An NTSB Senior Powerplants Investigator reviewed the report prepared by Pratt & Whitney following the field examination of the engine and maintenance records. He concurred with the report and commented on some of its findings. In summary, the engine was an assembled compilation of PWC and aftermarket (Parts Manufacturer Approval – PMA) parts. Some PMA parts installed were not authorized for the application, and the serial numbers reflected in the maintenance records did not match the components installed and reflected a compressor turbine stator (weld) repair that was not PWC approved. For example, the factory original compressor turbine disk was installed while the logbook indicated another disk was installed. The compressor turbine disk was a time-limited item, and the total hours on the installed disk could not be verified. Metallurgical examination of the compressor turbine bladesrevealed fracture features consistent with high-velocity impact and high-temperature deformation such as "creep." All blades were fractured, the primary fracture could not be identified, and therefore the sequence in which the fractures occurred could not be determined. ## Aircraft - Registration: [N4531K](https://openairdocs.org/deregistered/N4531K-2021-03-29), registration cancelled 2021-03-29, S/N 502-0102 (OpenAirDocs) - Reported make and model: AIR TRACTOR INC AT 502 (UNDESIGNAT) - Registry model: [Air Tractor AT-502](https://openairdocs.org/model/air-tractor-at-502) (registry code 0390303) (OpenAirDocs) - Registry engine: [Pratt & Whitney Canada PT6A-60A](https://openairdocs.org/engine/pratt-whitney-canada-pt6a-60a) (registry code 52043, turbo-prop) (OpenAirDocs) - Category: Airplane - Serial number: 502-0102 - Year built: 1990 - Airframe hours: 5490 - Engines: Pratt and Whitney PWC PT6A-15AG 750 horsepower turbo prop - Damage: Substantial damage - Flight: Aerial application, Part 137 - Operator: Londe Air LLC - Registered owner: Londe Air LLC - Airworthiness certificate: Special, Restricted (Special) - Departed: 1M7, Hickman, KY - Destination: 1M7, Hickman, KY - Equipment: Unknown ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 63; injuries: none; commercial; airplane ratings: single-engine land; instrument ratings: airplane; medical: class 2; last flight review January 7, 2016; seat: single; restraint: 4-point; flight hours: 18,000 total, 3,034 in this make and model ## Weather - Conditions: Visual (VMC), Day - Wind: 160° at 4 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 73 °F, dew point 68 °F - Altimeter: 30.05 inHg - Observed at: UCY, 6 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 20170915019409A](https://openairdocs.org/incident/20170915019409A), Sep 15, 2017: Air Tractor Inc AT-502, Union City, TN, Substantial damage. The commercial pilot was the sole occupant and pilot of aircraft N4531K that departed fulton county airport, Kentucky, Friday, September 15, 2017, at 0915… ## Docket (6 files) The files NTSB released with the investigation on June 17, 2020, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=96017. 26.6 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 Memo for Record (item 1, .PDF, 52 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40484443&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1%20Memo%20for%20Record-Master.PDF - Materials Laboratory Factual Report (item 2, .PDF, 22.6 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40484444&FileExtension=.PDF&FileName=Materials%20Laboratory%20Factual%20Report-Master.PDF - Record of Engine Teardown (item 3, .PDF, 2.5 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40484486&FileExtension=.PDF&FileName=Record%20of%20Engine%20Teardown-Master.PDF - Powerplants Memorandum for Record (item 4, .PDF, 59 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40484487&FileExtension=.PDF&FileName=Powerplants%20Memorandum%20for%20Record-Master.PDF - Photos (item 5, .PDF, 549 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40484488&FileExtension=.PDF&FileName=Photos-Master.PDF - Release of Aircraft Wreckage (item 6, .PDF, 880 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40484489&FileExtension=.PDF&FileName=Release%20of%20Aircraft%20Wreckage-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.