NTSB Factual Report

On August 19, 2005, approximately 1100 central daylight time, a single-engine Air Tractor AT-401 agricultural airplane, N4545W, sustained minor damage during a forced landing to a field shortly after take off from the Chambers County-Winnie Stowall Airport (T90), near Winnie, Texas. The commercial pilot, sole occupant of the airplane, was not injured. The airplane was registered to and operated by Twin County Air Ag Incorporated, of Winnie, Texas. No flight plan was filed for the flight destined for the Wharton Regional Airport (ARM), near Wharton, Texas. Visual meteorological conditions prevailed for the positioning flight conducted under 14 Code of Federal Regulations Part 91.

In a written statement, the 18,950-hour pilot stated that he departed Runway 17 and initiated a climbing turn to the southwest. When the airplane reached an altitude of 150 to 200 feet above the ground, he reduced power and the "engine blew." The pilot executed a forced landing to an open field adjacent to the airport.

The Honeywell TPE-331-2-201 turbine engine (serial number P-90315) was examined at the manufacturer's Investigation Laboratory, near Phoenix, Arizona, on October 13, 2005, under the supervision of a representative of the Federal Aviation Administration (FAA). Examination of the engine revealed an uncontained separation of the second-stage turbine disk. Three sections of the disk and four separated blades were submitted for material analysis. According to Honeywell's report, the fractured surfaces were examined optically and in a scanning electron microscope (SEM). Fracture features typical of low cycle fatigue were found emanating from the bore of the second-stage turbine disk and extended radially up to 0.82-inches into the disk. Low cycle fatigue also emanated from rotor rivet holes; however, the fatigue features in the rivet holes extended only 0.07-inches radially into the disk and were not considered primary to the disk separation. No evidence of deep scratches or gouges were observed on the bore surface or on the forward and aft face of the disk. A Senior Metallurgist from the National Transportation Safety Board reviewed Honeywell's report and concurred with their findings.

An FAA inspector, who reviewed the engine's maintenance records, reported that the engine had been previously installed on an aircraft that was registered in a foreign country. The maintenance records were not complete. When the operator purchased the engine, he informed the facility that performed his engine maintenance that the second-stage turbine rotor was installed on the engine in 1992 and had accrued a total of 730 cycles. The maintenance facility then produced a new life-limit card for the second stage turbine wheel. Based on this data, the wheel had accrued a total of approximately 1,738 cycles at the time it failed. However, according to Honeywell production records, the second-stage turbine rotor had originally been shipped with zero cycles in another, new production engine on January 24, 1973. The rotor had an FAA approved life-limit of 5,400 cycles.

NTSB Probable Cause

The loss of engine power due to the failure of the second-stage turbine wheel as a result of low cycle fatigue.