N6113CAir Tractor AT-502B · 1994

On August 8, 2019, about 0721 central daylight time, an Air Tractor AT-502B, N6113C, was destroyed when it was involved in an accident near Sumner, Iowa. The pilot was fatally injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 positioning flight.

The flight originated from the Mt. Pleasant Municipal Airport, Mt. Pleasant, Iowa, about 0615 and was destined for Oelwein Municipal Airport (OLZ), Oelwein, Iowa. A witness at OLZ reported that the pilot overflew the runway but then continued north. The airplane appeared to be intact, and the engine seemed to be running normally at that time.

Based on multiple witness statements, the airplane continued about 14 miles north of OLZ before it turned south. Witnesses located about 2-1/2 miles north of the accident site reported observing the airplane overfly their homes at a low altitude. One witness noted that the airplane appeared to be in level flight, and the engine seemed to be operating normally.

A witness near the accident site observed the airplane approach from the west-northwest in a constant 20° left turn. The airplane struck the power lines; however, the airplane's flightpath was not affected. The airplane then nearly struck a building before it struck a second set of power lines. It then veered left, and the nose dropped. The airplane subsequently impacted a road, skidded across the road, and impacted the ground near a large tree. A postimpact fire ensued. The witness added that nothing seemed to be unusual about the airplane before the initial wire strike except that it was at a “very low altitude.” The airplane seemed to be intact, and the engine sounded normal. He also stated that the airplane remained in the shallow left turn as it struck the power lines and did not appear to be climbing or descending.

The pilot's logbook was not available to the National Transportation Safety Board during the investigation. On his most recent medical certificate application, the pilot reported taking no medications and having diet-controlled diabetes. He was involved in a wire strike event in the accident airplane 8 days before the accident. Witnesses noted that after that wire strike, the pilot seemed shaken, and he was heard coughing and vomiting several days later.

The owner of an agriculture operation based at OLZ noticed damage to the propeller, windshield, and spray boom following the pilot’s previous wire strike. The airplane remained at OLZ until repairs were completed; the engine and propeller were removed, and the airplane was returned to service 3 days before the accident.

A maintenance entry dated August 5, 2019, indicated that the engine power section was removed for an unscheduled inspection due to a propeller strike. It was repaired, reinstalled, and approved for return to service.

Sunrise occurred at 0608. At the time of the accident, the sun was positioned about 12° above the horizon at an azimuth of 079° (relative to true north).

The owner of an agriculture operation based at OLZ noticed damage to the propeller, windshield, and spray boom following the pilot’s previous wire strike. The airplane remained at OLZ until repairs were completed; the engine and propeller were removed, and the airplane was returned to service 3 days before the accident.

A maintenance entry dated August 5, 2019, indicated that the engine power section was removed for an unscheduled inspection due to a propeller strike. It was repaired, reinstalled, and approved for return to service.

Damage to two sets of power lines, a small roof-mounted antenna on a single-story building, and a power line support pole was consistent with the airplane striking them before impacting a two-lane road and coming to rest against a large tree. The accident site was in the yard of a mixed-use commercial/residential building. The main wreckage consisted of the fuselage, right wing, inboard portion of the left wing, and empennage. The outboard portion of the left wing and the left aileron had separated and were located near the power line support pole. The engine, with the propeller attached, had separated from the airframe and was located at the accident site. A postimpact fire consumed most of the fuselage.

A postaccident airframe examination did not reveal any evidence of an in-flight structural failure or flight control system anomaly. An engine examination revealed circumferential contact marks throughout the engine consistent with rotation at impact. No anomalies consistent with a preimpact failure or malfunction were observed.

An autopsy conducted by the Iowa Office of the State Medical Examiner, Ankeny, Iowa, attributed the pilot's death to multiple blunt force injuries with thermal injuries. The autopsy identified evidence of heart disease, a subarachnoid hemorrhage that appeared to be several days old, pulmonary hypertension, and chronic kidney disease. Medical records revealed the pilot received dialysis for kidney disease and was being treated for diabetes, which his primary care doctor described as "not well controlled." In addition, the pilot had a history of coronary artery disease treated with stent placement and high blood pressure treated with medication.

Toxicology testing was performed by the Federal Aviation Administration Forensic Sciences Laboratory. The testing detected hydrocodone and dihydrocodeine, fentanyl and norfentanyl, trazodone, and yohimbine in heart blood and liver tissue.

Hydrocodone and fentanyl were prescribed to the pilot for chronic pain due to spinal stenosis. Both are in a class of medications referred to as opioid analgesics and have the potential to be impairing. Dihydrocodeine and norfentanyl are metabolites of hydrocodone and fentanyl, respectively. Trazodone was prescribed for anxiety. It is in a class of medications referred to as serotonin modulators and may impair the mental and/or physical ability required for the performance of potentially hazardous tasks. Yohimbine is used as a dietary supplement for multiple reasons including impotence, diabetic neuropathy, high blood pressure, and chest pain. It has stimulant effects and may impair mental and physical ability to perform hazardous tasks.

On July 15, 2013, about 1130 central daylight time, an Air Tractor AT-502B airplane, N6113C, was substantially damaged during a forced landing following a loss of engine power near Nauvoo, Illinois. The pilot was not injured. The airplane was registered to and operated by Air Advantage Inc. under the provisions of 14 Code of Federal Regulations Part 137 as an aerial application flight. Visual meteorological conditions prevailed for the flight, which was not operated on a flight plan. The local flight originated from Schilson Field Airport (IS51), Carthage, Illinois, about 1125.The pilot reported that after takeoff he proceeded 5 miles north toward the assigned agricultural field. As he was setting up for the initial spray run, he heard a "loud explosion" at which point the propeller stopped turning. He noted that metallic debris was emitted from the engine exhaust, which was followed by grinding noises from the engine. He executed a forced landing to a soybean field; however, the airplane overran the bean field and crossed into a corn field, at which time the right main landing gear collapsed. The airplane came to rest upright, with substantial damage to the right wing.

A postaccident engine examination revealed damage to the compressor turbine disc, power turbine disc, and the compressor turbine and power turbine guide vane rings and shrouds. Metallurgical examination determined that one compressor turbine blade exhibited features consistent with fatigue failure initiating at the trailing edge of the blade section, near the root. A majority of the fracture surface was obscured by corrosion products and metal splatter, which precluded a complete evaluation of the fracture surface. Metallographic examination of the trailing edge of the blade fracture surface revealed no material anomalies. The blade material and airfoil trailing edge thickness were determined to be within drawing requirements.

The remaining blades of the compressor turbine displayed gouges and fracture surfaces consistent with secondary impact damage and overstress failures. The power turbine blades were separated from the root to about two-thirds of the blade span. The fracture features were consistent with overstress separations of the blade sections. Five blades were not separated; these blades exhibited gouges consistent with secondary impact damage from the liberated blades. Scraping damage was observed on the compressor and turbine shrouds, which was consistent with blade contact during the engine failure sequence after the initial compressor blade failure.

The airplane was powered by a 750-shaft horsepower Pratt & Whitney Canada PT6A-34AG engine. At the time of the accident, the engine had accumulated about 9,961 hours since new, with about 7,336 hours since overhaul. The most recent recorded engine maintenance consisted of a 100-hour inspection completed on July 6, 2013, at 9,950 hours total time. The most recent engine hot section inspection was completed on December 31, 2012, at 9,782 hours total time.

Maintenance records indicated that the engine was removed and inspected due to excessive vibration in April 2008 at 7,132 hours engine total time. Damage to the power and compressor turbine blades and guide vane rings was observed. Overhauled power turbine blades and an overhauled power turbine guide vane ring were installed. New compressor turbine blades were installed at that time. The most recent engine overhaul was completed in April 2000 at 2,625 hours total time since new.

Based on the available engine maintenance records, the most recent review of engine start cycles was completed on December 22, 2012. At that time, the engine had accumulated 9,752 hours total time, with 5,634 engine start cycles consumed. The compressor turbine start cycle limit was 16,000.