Sunday, February 09, 2020

Loss of Engine Power (Partial): Air Tractor AT-401, N4532F; accident occurred August 24, 2017 in Pearsall, Frio County, Texas

The No. 9 engine cylinder viewed from the aft side, as received. 

The No. 9 engine cylinder viewed from the forward side, as received.

The pushrod tubes on the forward side of the engine, showing denting damage.

View of the aft spark plug, showing denting damage and the end of the crack between two cooling fins.

The crack in the cylinder showing the largest opening.

The cylinder crack, viewed from the forward side.

View of the other end of the cylinder crack.

View of the fracture surfaces of the cylinder crack, after laboratory opening. 

The outboard mating fracture surface, annotated to show the different fracture regions.

The progressive area of the outboard fracture surface, using oblique lighting.

The inboard mating fracture surface, annotated to show the different fracture regions.

The fatigue area of the outboard fracture surface, using oblique lighting.

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

Additional Participating Entity:

Federal Aviation Administration / Flight Standards District Office; San Antonio, Texas

Aviation Accident Factual Report - National Transportation Safety Board:

Investigation Docket - National Transportation Safety Board:

Location: Pearsall, TX
Accident Number: CEN17LA330
Date & Time: 08/24/2017, 1000 CDT
Registration: N4532F
Aircraft: AIR TRACTOR INC AT 401
Aircraft Damage: Substantial
Defining Event: Loss of engine power (partial)
Injuries: 1 None
Flight Conducted Under: Part 137: Agricultural 

On August 24, 2017, about 1000 central daylight time, an Air Tractor AT-401, N4532F, impacted terrain during a forced landing following a partial loss of engine power near Pearsall, Texas. The commercial pilot was not injured, and the airplane was substantially damaged. The airplane was registered to and operated by Fitch's Flying Service as a Title 14 Code of Federal Regulations Part 137 without a flight plan. Day visual meteorological conditions prevailed for the local agricultural application that departed from McKinley Field Airport (T30), Pearsall, Texas, at 0900.

The pilot reported that the airplane experienced a partial loss of engine power during a low-altitude spray run over a field. He noted that the engine was surging and that he was unable to regain normal engine operation. He climbed to 100 ft above ground level, jettisoned the airplane's chemical load, but the engine operation still did not improve. The pilot reported that he subsequently made a forced landing to a nearby field. The pilot stated that the airplane decelerated rapidly and nosed over when it descended into tall vegetation and landed in soft sandy soil. The vertical stabilizer and rudder were substantially damaged.

A postaccident examination revealed a circumferential fracture of the No. 9 cylinder. The fractured cylinder, serial number (s/n) 4 4HN52 L215, was submitted to the National Transportation Safety Board's Materials Laboratory for additional examination. The laboratory examination revealed a large circumferential crack through the cylinder housing. The crack was located at the valley between two air cooling fins and through the forward spark plug hole. The crack measured circumferentially as 26.3 inches long, with about 5.6 inches of the remaining cylinder circumference uncracked. The widest opening of the crack was located about 8.5 inches from the bottom side of the inboard flange, and 10.5 inches from the bottom opening of the cylinder. The fracture faces exhibited features consistent with prolonged exposure to exhaust and combustion gasses for different lengths of time. Further examination revealed crack arrest and ratchet marks consistent with progressive cracking from multiple crack initiation sites. There were no discernable discrepancies, such as corrosion pits, wear marks, or machining marks present at the crack initiation sites. The crack had prorogated from the outer cylinder surfaces inward. Further examination of the crack features using a scanning electron microscope revealed fatigue striations consistent with fatigue cracking. A sample of the cylinder was tested using energy dispersive x-ray spectroscopy and x-ray fluorescence, which confirmed the material composition was consistent with an AA 200-series aluminum casting alloy. Additionally, hardness measurements were consistent with a casted AA 200-series aluminum alloy material.

The engine, a Pratt & Whitney R-1340AN-1, s/n 41-12807, had accumulated 8,899.2 hours since new and 1,310.1 hours since the last overhaul on March 5, 2009. A complete service history for the No. 9 cylinder could not be determined with the available logbook documentation. The No. 9 cylinder was not replaced or repaired during the 2009 overhaul. Based on available documentation, the No. 9 cylinder was not removed or repaired since the 2009 overhaul. According to the engine logbook, on August 1, 2017, about 64 hours before the accident, the engine cylinders were inspected in accordance with airworthiness directive No. 99-11-02 to verify that there were no visible cylinder cracks, and the corresponding logbook entry indicated "no cracks found."

Pilot Information

Certificate: Commercial
Age: 33, Male
Airplane Rating(s): Single-engine Land
Seat Occupied: Center
Other Aircraft Rating(s): None
Restraint Used:
Instrument Rating(s): None
Second Pilot Present: No
Instructor Rating(s): None
Toxicology Performed: No
Medical Certification: Class 2 Without Waivers/Limitations
Last FAA Medical Exam: 05/09/2017 
Occupational Pilot:Yes
Last Flight Review or Equivalent: 03/10/2017
Flight Time:  609 hours (Total, all aircraft), 290 hours (Total, this make and model), 545 hours (Pilot In Command, all aircraft), 220 hours (Last 90 days, all aircraft), 108 hours (Last 30 days, all aircraft), 3 hours (Last 24 hours, all aircraft) 

Aircraft and Owner/Operator Information

Aircraft Make: AIR TRACTOR INC
Registration: N4532F
Model/Series: AT 401 UNDESIGNATED
Aircraft Category: Airplane
Year of Manufacture:1990 
Amateur Built: No
Airworthiness Certificate: Restricted
Serial Number: 401-0769
Landing Gear Type: Tailwheel
Seats: 1
Date/Type of Last Inspection: 03/01/2017, Annual
Certified Max Gross Wt.: 7860 lbs
Time Since Last Inspection: 264 Hours
Engines: 1 Reciprocating
Airframe Total Time: 6228.1 Hours at time of accident
Engine Manufacturer: Pratt & Whitney
ELT: Not installed
Engine Model/Series: R-1340AN-1
Registered Owner: Fitch's Flying Service
Rated Power: 600 hp
Operator: Fitch's Flying Service
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: COT, 474 ft msl
Distance from Accident Site: 20 Nautical Miles
Observation Time: 0953 CDT
Direction from Accident Site: 180°
Lowest Cloud Condition:
Visibility:  10 Miles
Lowest Ceiling: Broken / 12000 ft agl
Visibility (RVR):
Wind Speed/Gusts: 5 knots /
Turbulence Type Forecast/Actual: None / None
Wind Direction: 120°
Turbulence Severity Forecast/Actual: N/A / N/A
Altimeter Setting: 29.92 inches Hg
Temperature/Dew Point: 28°C / 22°C
Precipitation and Obscuration: No Obscuration; No Precipitation
Departure Point: Pearsall, TX (T30)
Type of Flight Plan Filed: None
Destination: Pearsall, TX (T30)
Type of Clearance:None 
Departure Time: 0900 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: 28.876389, -99.005278 (est)

1 comment:

  1. nothing unusual, have seen that on a couple of T-6s, Engine will run fine below 28inches, anything above that it backfires and blows white smoke. The last time it happened it occurred on take off, landed on the remaining runway, and the engine sounded normal, until above 28 inches