Pearisburg, VA, USA
N4506L
AIR TRACTOR 402A
The Air Tractor was spreading chemical when the pilot observed orange flames and black smoke emitting from the engine exhausts. The engine lost power, he feathered the propeller, and set up for a forced landing in a nearby open field. The airplane touched down, rolled a short distance, and struck embedded rock. The landing gear collapsed, the fuselage was wrinkled, and the propeller separated from the engine. Examination of the PWC PT6A-20 engine revealed several compressor turbine blades had fractured and been released into the engine gas path. The blades also impacted adjacent and downstream components. The compressor turbine blades used in the engine were not approved by PWC; however, they were PMA manufactured with FAA approval. Since engine overhaul, the engine had accumulated 10,978.8 hours and 15,059 cycles. According to the FAA, the PWC recommended overhaul time of 3,600 hours. The airplane was being operated on a USDA Forest Service contact that required the engine to have been overhauled within the manufacturer's specifications. The engine's time since overhaul was not discovered by the Forest Service when they accepted the airplane for use on their contract.
On June 26, 2003, at 0952 eastern daylight time, an Air Tractor 402A, N4506L, under contract to the USDA Forest Service, was substantially damaged during a forced landing in Pearisburg, Virginia. The certificated commercial pilot was not injured. Visual meteorological conditions prevailed for the local flight that departed from New River Valley Airport, Dublin, Virginia (PSK). The aerial application flight was conducted on a visual flight rules (VFR) company flight plan under 14 CFR Part 91. The pilot reported that the purpose of the flight was Gypsy Moth pheromone flake dispersal, under the direction of the U.S. Forest Service. He departed from New River Valley at 07:49 and proceeded to Narrows, Virginia, the treatment location. He further stated: "...The engine emitted orange flame and black smoke from both exhaust stacks and stopped running. I made a left descending turn, pulled the prop control to feather the prop and found a place to make an off airport landing with the altitude and airspeed available. The landing was hard onto rocks within a very short distance. I exited the aircraft immediately as I had 100+ gallons of fuel on board and the fuel tanks were ruptured on landing...." The pilot was picked up by a Virginia State Police helicopter and taken to a local hospital for observation. According to an inspector from the Federal Aviation Administration (FAA), the airplane touched down, rolled a short distance, and struck rocks embedded in the ground. The landing gear collapsed rearward, the fuselage was wrinkled, and the propeller separated from the engine. The engine was forwarded to the Pratt & Whitney Canada (PWC) facility in Bridgeport, West Virginia for further examination under the supervision of an FAA airworthiness inspector. The report from PWC stated in part: "...The engine lost useful power as a result of the fracture and release of one or several compressor turbine blades into the engine gas path, and their subsequent impact with the adjacent and downstream components...." The report also stated: "...The blades were identified as Doncasters Turbo Products P/N T-023401 units, manufactured under Federal Aviation Administration Parts Manufacturer Approval (FAA PMA). However, the part was not approved for use in the engine by PWC. According to the type certificate data sheet (TCDS) for the engine, the overhaul time for the engine was 3,600 hours. According to an email from the FAA, the operator was not required to observe the engine overhaul time specified in the TCDS for the engine. The engine was reported to have a total time of 27,047.4 hours, including 10,978.8 hours, and 15,059 cycles since overhaul. The last hot section inspection was conducted 285.3 hours prior to the accident. The contract that the airplane was being operated under specified in part: "...Aircraft shall not be approved if any engine, component, or propeller time in service exceeds the manufacturers recommended time between overhaul...." The discrepancy between actual engine time since overhaul, and that allowed by the Forest Service Contract was not discovered when the Forest Service examined the airplane, its records, and accepted it for use on the contract.
A compressor turbine blade fracture which resulted in a power loss, and forced landing. Factor were the rocks in the landing area, and the operator's decision to operate the engine beyond the engine manufacturer's recommendations for overhaul.
Source: NTSB Aviation Accident Database
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