Firebaugh, CA, USA
N4009M
Ayres S2R
The airplane impacted soft muddy terrain during a forced landing following a loss of engine power shortly after departure. The pilot departed with a full load of fertilizer and climbed above several transmission wires before the engine lost power. The airplane pitched down in a nose-low configuration and dove toward terrain. The engine's most recent inspection occurred about 2 months prior to the accident. The logbook entry for that inspection stated that the mechanic performed a hot section inspection at which time the compressor turbine (CT) disk was reinstalled with 3,595 cycles remaining. A post accident examination of the engine revealed that a CT blade had failed in fatigue initiating in the fir tree root. Near the fatigue origin, no surface damage was observed and no material anomalies were found on the fracture surface; the reason for the fatigue failure was never definitively determined. The blade was likely manufactured under a Parts Manufacturer Approval (PMA). The Safety Board Materials Laboratory reported that the chemistry of the fractured blade appeared to be consistent with the PMA specified alloy and not to the material specification the original equipment manufacturer (OEM) utilizes. A review of the Safety Board database revealed an instance of a very similar failure on an OEM manufactured CT blade. Evidence of recent marijuana use was found on toxicological evaluation, and the pilot might have been impaired ..." It is not clear whether this impairment adversely affected the pilot's actual actions during his response to the loss of engine power.
HISTORY OF FLIGHT On February 18, 2005, at 0811 Pacific standard time, an Ayres S2R, N4009M, impacted soft muddy terrain shortly after departing Firebaugh Airport, Firebaugh, California. Vance Ag was operating the airplane under the provisions of 14 CFR Part 137 as a local aerial application flight. The commercial pilot, the sole occupant, sustained fatal injuries; the airplane sustained substantial damage. Visual meteorological conditions prevailed, and a flight plan had not been filed. According to the operator, the accident flight was to be the pilot's fourth flight of the day in that airplane. The pilot had landed just prior to the accident, and subsequently departed with a full load of Urea fertilizer. During a telephone conversation with a National Transportation Safety Board investigator, a witness stated that while exiting his office on the north end of the airport, he observed the accident airplane depart the runway. After the airplane climbed above several transmission wires, the engine made two "tszzz" whirling sounds, and subsequently became silent. The airplane pitched down in a nose-low configuration and dove toward terrain. The pilot initially egressed the airplane, but succumbed to his injuries about 30 minutes thereafter. A Federal Aviation Administration (FAA) inspector examined the airplane after the accident occurred. He stated that the propeller blades did not exhibit any high energy impact signatures, and remained straight. While conducting an examination of the airplane he noted that the seatbelt was separated. AIRCRAFT INFORMATION The airplane was an Ayres S2R-T34, serial number 6012. A review of the airplane's logbooks revealed that the airframe had undergone a 100-hour inspection on August 26, 2004, at a total time of 11,193.4 hours. The airplane was powered by a Pratt & Whitney PT6A-34AG turboprop engine (serial number 56561) that had accumulated an estimated total time of 17, 215 hours since manufacture (May 1979). A review of the engine logbooks revealed that the last engine overhaul was performed on August 24, 2003, at the airplane's Hobbs time of 9,701.1 hours. At that time the compressor turbine (CT) disk was installed (serial number 1M560) with 10,012 cycles already consumed (a notation stated 5,988 cycles remained ). The engine's most recent inspection occurred on December 30, 2004. The entry indicated that the mechanic preformed a hot section inspection at which time the CT disk was reinstalled with 3,595 cycles remaining. The airplane was configured with one pilot seat located directly in the middle of the cockpit. The control stick is oriented in front of the seat, between the pilot's legs. A representative for the airplane manufacturer stated that the seat and seatbelts/shoulder harnesses involved in the accident were not tested by Thrush Aircraft, Inc., or its predecessors, because the seat was qualified to Technical Standard Order (TSO) C39 and the belts to TSO C22F, which occurred prior to Thrush Aircraft's involvement and testing of restraint systems. As a reference, the representative further stated that the installation of seats used before the ones installed on the accident airplane were tested by Thrush Aircraft, Inc., to loads specified by Civil Aviation Regulation (CAR) 3.186, with CAR 3.190 fitting factors and CAM 8 loads. This corresponds to the installation being tested in the up direction to 3.0 x 1.33 = 3.99g, in the down direction to 3.8 x 1.33 x 1.5 = 7.58g, in the side direction to 3.0g, and in the forward direction to 9.0 x 1.33 = 11.97g. The representative further stated that the shoulder harnesses were introduced after the original certification, and their installation structure was analyzed for a 190-pound person to a forward g-load of 9.0. MEDICAL AND PATHOLOGICAL INFORMATION The Fresno County Coroner performed an autopsy on the pilot. A review of the autopsy report disclosed that there were no visible external injuries to the head or neck area of the pilot. He sustained injuries to his abdomen with the report noting an abrasion (4 inches by 0.5 inches) and contusion (3.5 inches by 1.5 inches) on the right side. It was also noted that the sternum was fractured at its upper 1/3, with extravasations of blood over his chest area. Blood was also located in the chest cavity. The pilot's spleen was severely lacerated. The autopsy report additionally noted significant contusions on the pilot's legs, around the knee and thigh area. The pelvic bones were intact. The forensic pathologist who preformed the autopsy opined that the cause of death was, "chest and abdominal trauma due to blunt impact." The Fresno County's toxicological testing results were positive for Delta-9-THC at the level noted of 45 ng/ml and 9-Carboxy-11-nor-Delta-9 at a level of 720 ng/ml. The FAA Toxicology and Accident Research Laboratory additionally performed toxicological testing of specimens of the pilot. The results of analysis of the pilot's specimens were negative for ethanol, carbon monoxide, and cyanide. The testing found tetrahydrocannabinol (marihuana) in both the blood and liver specimens at levels of 0.0075 (ug/ml, ug/g) and 0.023 (ug/ml, ug/g), respectively. It additionally revealed tetrahydrocannabinol carboxylic acid in the blood and liver specimens at levels of 0.1219 (ug/ml, ug/g) and 0.1626 (ug/ml, ug/g), respectively. TEST AND RESEARCH Engine Examination. The engine was shipped to Pratt & Whitney Canada for examination. Under the auspices of a Transportation Safety Board of Canada investigator, the engine was disassembled at the Montreal facilities on May 10 and 11, 2005. The compressor first stage rotor appeared intact, showing no indications of distress. The compressor turbine (CT) blades were all missing material at the tips, varying in heights. One blade was fractured below the fir tree area and was significantly shorter than the other blades. The CT shroud displayed molten material with gouging on the sides. The power turbine (PT) guide vane airfoil leading edges displayed nicks and gouge marks consistent with contact from separated compressor turbine blade debris. A majority of the PT blades were fractured at varying heights and displayed characteristics of contact with separated CT blade debris and contact with the PT shroud. The remaining blades and PT guide vane displayed circumferential rubbing; the external housing had been deformed, which appeared to be a result of impact damage. Blade Examination. Personnel from the Safety Board Materials Laboratory examined the fracture face of the subject CT blade. The fracture surface appeared smooth with a curving boundary, typical of fatigue. Near the fatigue origin, no surface damage was observed and no material anomalies were visible on the fracture surface. The facture was located above the region of fretting noted in the fir tree root. The manufacturer of the blade could not be positively established from the limited portion of the blade that remained. The part number (T-102401-100A) on other blades in the set indicated that they were manufactured by Turbo Products, a Division of Doncasters, Inc., who are the sole Parts Manufacturer Approval (PMA) manufacturer for the blades. The remaining blades were all machined with heat code identification of 13CBF. Personnel from the Safety Board Materials Laboratory further reported that the chemistry of the fractured blade appeared to be consistent with the PMA specified alloy and not to the material Pratt & Whitney Canada utilizes for manufacturer. A review of the Safety Borad database revealed an instance of a very similar failure on a Pratt & Whitney Canada manufactured CT blade (see accident number SEA00LA160). A representative from the blade manufacturer stated that the heat code on the surrounding blades corresponded to a batch of blades manufactured in mid 2004. He stated that the blades were shipped from their facility between August 4 and September 14, 2004. Seat Belt Examination. The separated seatbelt was sent to the FAA Civil Aerospace Medical Institute Biodyamics Lab for examination. The seatbelt, a four-point restraint system, consisted of a 3-inch wide lap belt and dual 2-inch wide shoulder straps. The shoulder straps had their own respective inertia reels and connected to the lap belt at a center latch. The TSO tags on both straps were faded and illegible. The right lap belt was faded with different hues displaying evidence of environmental exposure. The webbing was frayed at the adjuster bar and the metal latch tongue had markings that the inspector stated was consistent with heavy loading. The upper portion of the belt was disintegrated from the tongue to 2 inches down the length of the belt. The belt length showed minor fraying along the bottom edge at the adjuster bar and the latch tongue. The left lap belt was torn where the webbing passed through the adjustment mechanism. The inspector stated that the pattern of the webbing tear indicated that the tear initiated at the top edge where it passed over the bar. The FAA's lab inspector stated that minor fraying of the lower edge of the lap belt's webbing was consistent with normal wear. The severe fraying (disintegration) of the upper portion of the right belt and the separation of the webbing at the adjuster on the left lap belt is consistent with heavy loading during the accident sequence. He further stated that the entire belt appeared to be contaminated with chemicals. The reduction in webbing strength due to chemical and normal ultra violet (UV) light exposure was unknown. There was not enough section of undamaged webbing to perform a static strength test. A review of the airframe logbooks revealed that on April 4, 1995, a mechanic made a notation specifically notating that the seat belts were inspected during his 100-hour inspection; the Hobbs time was entered to be 1,722.8 hours.
the loss of engine power during takeoff climb resulting from the fatigue failure of one of the compressor turbine blades; the cause of the fatigue failure could not be definitively determined.
Source: NTSB Aviation Accident Database
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