Air Tractor INC AT 502 accident near Union City, Tennessee, September 15, 2017
On September 15, 2017 at about 2:15 pm local time, a 1990 Air Tractor INC AT 502, registered N4531K, was substantially damaged in an accident during enroute (cruise) near Union City, Tennessee. It was an aerial application (crop spraying) flight under agricultural flying rules (Part 137). No one was hurt; 1 person was on board or involved. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
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.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- September 15, 2017 · about 2:15 pm local time
- Place
- Union City, Tennessee · map
- Type
- Accident
- Injuries
- No one was hurt; 1 person was on board or involved.
- Weather
- visual conditions (good weather)
- Aircraft
- Air Tractor INC AT 502 UNDESIGNAT, built 1990 · all AT 502s on the register
- Registration
- N4531K · no longer on the register · serial 502-0102
- Damage
- Substantial damage
- Flight
- Aerial application (crop spraying) flight · agricultural flying rules (Part 137)
The NTSB's narrative final · quoted from the NTSB record
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.
The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.
The factual record from the NTSB's investigation tables, in plain English
What happened, in order
- Loss of engine power (total) during enroute (cruise) defining event
- Off-field or emergency landing during emergency descent
- Part(s) separation from AC during landing
The NTSB's findings
- cause Aircraft › Aircraft power plant › Engine (turbine/turboprop) › (general) › Failure
- factor Aircraft › Aircraft power plant › Power plant › (general) › Incorrect service/maintenance
Pilot
- Certificate: commercial pilot
- Ratings: single-engine land; instrument: airplane
- Flight time: 18,000 hours in all; 3,034 in this make and model
- Last flight review: January 7, 2016
- Medical certificate: Class 2
- Seat: sngl
- Injury: no injuries
The aircraft
- Airframe total time: 5,490 hours
- Seats: 1
- Landing gear: fixed
- Engine: Pratt And Whitney PWC PT6A-15AG (turboprop); 0 hours total
- Operator: Londe Air LLC
The flight
- Departed from: 1M7 Hickman KY at 2:15 pm
- Destination: 1M7 Hickman KY
- Flight plan: none
Weather at the time
- Light: daylight
- Wind: from 160° at 4 knots
- Visibility: 10 statute miles
- Sky: clear
- Temperature: 73°F (23°C), dew point 68°F (20°C)
- Altimeter: 30.05 inHg
- Observation at 2:15 pm from UCY, 6 miles away
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Flight crew | 1 |
Documents from the investigation the NTSB's docket: the evidence folder behind the report
6 documents, released by the NTSB on June 17, 2020. View them here, or download them; the NTSB redacts some personal details before release, and this site shows the NTSB's own titles rather than its file names.
| # | Document | What it is | |
|---|---|---|---|
| 1 | Pilot/operator Aircraft Accident Report, NTSB Form 6120.1 Memo for Record | PDF, 1 page | View Download |
| 2 | Materials Laboratory Factual Report | PDF, 45 pages | View Download |
| 3 | Record of Engine Teardown | PDF, 30 pages | View Download |
| 4 | Powerplants Memorandum for Record | PDF, 1 page | View Download |
| 5 | Photos | PDF, 3 pages | View Download |
| 6 | Release of Aircraft Wreckage | PDF, 1 page | View Download |
The same docket at the NTSB · documents without a copy here are fetched from the NTSB when you open them.
Everything on this page comes from the NTSB's public records. The narrative, probable cause and findings are the NTSB's own words; the coded tables behind the report are written out in plain English, with pilots' ages, home towns and medical details left out. The documents and photographs are the NTSB's docket, shown as the NTSB released them. This site's own text never names anyone involved. A preliminary report can change; the final report usually follows one to two years later, and the page is refreshed when it does.