Cary, MS, USA
N1027V
Air Tractor AT-402
The 9,901-hour commercial pilot lost control of the tail wheel-equipped airplane while performing aerial application. According to the pilot, the engine produced an "explosion" like noise prior to a total loss of engine power. The pilot was then forced to land the airplane in a cotton and soybean field. Upon landing, the airplane sustained damage to the propeller blades, both main landing gears, both wings, the fuselage, and the vertical stabilizer. The pilot reported that at the time of the mishap the airplanes' altitude was approximately be 5 to 10 feet above ground level, resulting in a lack of suitable terrain for forced landing. Teardown and examination of the engine revealed the failure was initiated by a compressor turbine guide vane ring crack at a weld repair that released material into the compressor turbine blades.
On August 20, 2007, about 0900 central daylight time, a tail wheel-equipped Air Tractor AT-402 airplane, N1027V, sustained substantial damage following a total loss of engine power while performing aerial application near Cary, Texas. The commercial pilot, the sole occupant of the airplane, sustained minor injuries. The airplane was registered and operated by the commercial pilot under the provisions of 14 CFR Part 137. Visual meteorological conditions prevailed, and no flight plan had been filed. The 9,901-hour commercial pilot reported that while performing aerial application at 5 to 10 feet above ground level the single-engine airplane produced an "explosion sound" from the engine. Following the noise, the pilot experienced a total loss of engine power. The pilot performed an emergency landing on a flat field composed of cotton and soybean plants. The pilot was able to exit the airplane unassisted sustaining only minor injuries. A Federal Aviation Administration (FAA) safety inspector, who traveled to the accident site, reported that the airplane sustained damage to the propeller blades, both main landing gears, both wings, the fuselage, and the vertical stabilizer. The turbine-powered airplane was recovered to a secured location for further examination. The engine was examined in Clinton, Arkansas. The compressor turbine guide vane ring, displayed battering, gouges, tearing, and burning on the airfoil trailing edges due to contact with separating compressor turbine blade debris. One vane airfoil at the approximate 7:00 position displayed severe burning and a chord wise separation from the approximate mid-chord position to the trailing edges. The vane leading edges displayed no burning and or coating loss. The compressor turbine shroud displayed severe battering and gouges due to contact with separated compressor turbine blade debris. The compressor turbine assembly showed that the blade airfoils were fractured from the root to approximately 3/4 span, and displayed severe battering and gouging, with impact cracking along the trailing edges. Under macroscopic inspection all fracture surfaces displayed course dendritic surfaces characteristic of overload fracture. The upstream side blade platforms displayed light circumferential rubbing across approximately 1/3 of the disc circumference due to contact with the compressor turbine guide vane ring. The power turbine guide vane ring airfoils were battered due to contact with separated compressor and power turbine blades. The interstage baffle displayed contact marks and was slightly displaced due to contact with the power turbine. The power turbine shroud displayed severe battering and gouging due to contact with separated power turbine blade debris. The failed engine parts were further examined in Montreal, Canada. That examination showed evidence indicating the compressor turbine guide vane ring cracked at a weld repair and released material into the compressor turbine blades. The pilot reported that he accumulated 300-hours in the last 90 days, and 150-hours in the last 30 days. He had 4,600-hours in this make and model. At 0853 CDT an automated weather observation station in Vicksburg, Mississippi (KTVR), which was located 32 nautical miles (nm) of the accident site reported: skies clear; visibility 9 statue miles; winds from 170 degrees at 8 knots; temperature 28 degrees Celsius; dew point 22 degrees Celsius; altimeter 30.06 inches of Mercury.
The total loss of engine power due to a power turbine failure. Contributing to the accident were the lack of suitable terrain available to pilot for the forced landing and the low altitude.
Source: NTSB Aviation Accident Database
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