Sunday, June 28, 2020

Loss of Engine Power (Total): Air Tractor Inc AT-502, N4531K; accident occurred September 15, 2017 in Union City, Obion County, Tennessee

Photograph of wreckage as discovered. 
Courtesy of Federal Aviation Administration

Photograph of aircraft wreckage as discovered.
Courtesy of Federal Aviation Administration

Aft photo of wreckage as discovered. 
Courtesy of Federal Aviation Administration

The National Transportation Safety Board did not travel to the scene of this accident.

Additional Participating Entities:

Federal Aviation Administration / Flight Standards District Office; Memphis, Tennessee
Pratt & Whitney

Aviation Accident Factual Report - National Transportation Safety Board:

Investigation Docket - National Transportation Safety Board:

Location: Union City, TN
Accident Number: ERA17LA326
Date & Time: 09/15/2017, 0915 CDT
Registration: N4531K
Aircraft: AIR TRACTOR INC AT 502
Aircraft Damage: Substantial
Defining Event: Loss of engine power (total)
Injuries: 1 None
Flight Conducted Under: Part 137: Agricultural 

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 blades revealed 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. 

Pilot Information

Certificate: Commercial
Age: 63, Male
Airplane Rating(s): Single-engine Land
Seat Occupied: Single
Other Aircraft Rating(s): None
Restraint Used:
Instrument Rating(s): Airplane
Second Pilot Present: No
Instructor Rating(s): None
Toxicology Performed: No
Medical Certification:Class 2 
Last FAA Medical Exam: 03/28/2017
Occupational Pilot:Yes 
Last Flight Review or Equivalent: 01/07/2016
Flight Time:  18000 hours (Total, all aircraft), 3034 hours (Total, this make and model) 

Aircraft and Owner/Operator Information

Aircraft Make: AIR TRACTOR INC
Model/Series: AT 502 UNDESIGNATED
Aircraft Category: Airplane
Year of Manufacture: 1990
Amateur Built:No 
Airworthiness Certificate: Restricted
Serial Number: 502-0102
Landing Gear Type:Tailwheel 
Seats: 1
Date/Type of Last Inspection:
Certified Max Gross Wt.:
Time Since Last Inspection:
Engines: 1 Turbo Prop
Airframe Total Time: 5490 Hours at time of accident
Engine Manufacturer: Pratt and Whitney
Engine Model/Series: PWC PT6A-15AG
Registered Owner: LONDE AIR LLC
Rated Power: 750 hp
Operating Certificate(s) Held: Agricultural Aircraft (137)

Meteorological Information and Flight Plan

Conditions at Accident Site: Visual Conditions
Condition of Light: Day
Observation Facility, Elevation: UCY, 341 ft msl
Distance from Accident Site: 6 Nautical Miles
Observation Time: 0915 CDT
Direction from Accident Site: 97°
Lowest Cloud Condition: Clear
Visibility:  10 Miles
Lowest Ceiling: None
Visibility (RVR):
Wind Speed/Gusts: 4 knots /
Turbulence Type Forecast/Actual:
Wind Direction:160° 
Turbulence Severity Forecast/Actual: / N/A
Altimeter Setting: 30.06 inches Hg
Temperature/Dew Point: 23°C / 20°C
Precipitation and Obscuration: No Obscuration; No Precipitation
Departure Point: Hickman, KY (1M7)
Type of Flight Plan Filed: None
Destination: Hickman, KY (1M7)
Type of Clearance: None
Departure Time: 0915 CDT
Type of Airspace: Class G

Wreckage and Impact Information

Crew Injuries: 1 None
Aircraft Damage: Substantial
Passenger Injuries:N/A 
Aircraft Fire:None 
Ground Injuries: N/A
Aircraft Explosion: None
Total Injuries:1 None 
Latitude, Longitude:  36.392778, -89.116667 (est)