Danville, KY, USA
N740JB
BOARD JAMES A ZENITH 601 HD
The pilot, who also the owner/builder of the experimental, amateur-built airplane, was conducting the airplane's first test flight. The pilot stated that, during the takeoff roll, the airplane used about half of the runway surface, or five times the distance of a nominal takeoff roll, before becoming airborne. He added that the airplane then climbed to about 350 ft, at which point the flight controls began to feel "mushy." The airplane then entered a descent and impacted wires and trees before coming to rest in an open field. The pilot reported that the engine was producing full power throughout the flight but that the airplane would neither climb nor maintain altitude. Postaccident examination and testing of the airplane revealed that the pilot had likely misread the propeller adjustment tool when installing and adjusting the pitch of the ground-adjustable propeller and had inadvertently set the blades to an extremely low pitch. The low pitch of the propeller blades resulted in inadequate engine thrust, as evidenced by the long takeoff roll and the airplane's inability to climb.
On August 7, 2015, at 1910 eastern daylight time, an experimental, amateur-built Zenith 601HD, N740JB, was substantially damaged during a forced landing after takeoff from Stuart Powell Field (DVK), Danville, Kentucky. The sport pilot/owner/builder was not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the local test flight, which was conducted under the provisions of Title 14 Code of Federal Regulations Part 91.The pilot was interviewed by a Federal Aviation Administration (FAA) aviation safety inspector, and he also provided written statements. According to the pilot, the accident flight was the first flight for the airplane. After trailering the airplane to the airport and assembling it, he taxied it several times to become accustomed to the flight controls. Because "nothing felt out of place," he elected to take off. The departure runway was 5,000 feet long, and the pilot stated the takeoff roll used approximately 2,500 feet of the runway prior to rotation. He said the airplane climbed to about 350 feet agl before its handling characteristics felt "mushy," the climb stopped, and the airplane entered a descent he could not arrest. According to the pilot, he maneuvered the airplane away from houses and towards an open field but struck wires, trees, and terrain prior to reaching the field. He reported the engine was producing full power, but the airplane would neither climb nor maintain altitude. The pilot held a sport pilot certificate with a rating for airplane single engine land. He reported 124 total hours of flight experience, of which 5 hours were in the accident airplane make and model. In an interview with the FAA inspector, a flight instructor stated he completed a flight review with the pilot in May 2015. According to the flight instructor, the results of the flight were such that he could not endorse the pilot for a satisfactory review. The airplane was issued an FAA airworthiness certificate in July 2014, and was powered by a Chevrolet Corvair, 100-horsepower, 6-cylinder engine equipped with a ground-adjustable, two-bladed, composite propeller. Examination of the engine, propeller, and associated logbooks for each by the FAA inspector revealed that the engine's camshaft was changed, which may have affected the engine's timing. Further, according to the propeller logbook, the pilot had adjusted the pitch of the propeller blades to 9 degrees. After the airplane was released to the pilot, he completed some evaluations and trouble-shooting, and shared his findings. He further granted permission to share his findings with a manufacturer of Corvair engine conversion kits for airplanes for his review. The pilot/owner checked the engine's timing, and confirmed that it was correct, and that the engine ran properly. He also consulted with other builders of the accident airplane make/model, who suggested that the propeller pitch was set incorrectly. According to the engine kit manufacturer, propeller pitch is measured in degrees, and reflects the difference in pitch between the hub and the tip of the propeller blade. The propeller manufacturer provided a protractor with which to measure this angle and adjust the blade pitch. A higher blade pitch lowered the static rpm of the engine, while a lower blade pitch raised the static rpm. However, according to the pilot, the blade pitch and corresponding rpm readings from the accident airplane taken before the accident flight were 3,800 rpm at 12 degrees, and 3,200 rpm at 9 degrees. After the accident flight, he stated that he adjusted the blade angle to 7 degrees, which provided a static rpm of 2,800. These figures were contrary to known performance results during ground and flight testing by the engine manufacturer, and suggested the pilot's misreading of the protractor adjustment tool. The engine kit manufacturer stated that previous ground and flight testing with an airplane equipped similarly to the accident airplane suggested a thrust output of about 347 lbs at 2,550 rpm, with a propeller pitch setting of 11.5 degrees. A representative of the engine kit manufacturer stated that a static rpm reading of 3,800 as reported by the pilot "should have been a red flag as being 1000 rpm above anything discussed in the world of Corvairs." He also stated that the accident airplane's performance was consistent with a propeller blade angle of around 2 to 4 degrees. A propeller pitch setting of 7 degrees with a properly running engine would result in a ground roll of about 500 feet prior to lift off. ADITIONAL INFORMATION FAA Advisory Circular 90-89A, the Amateur-Built Aircraft and Ultralight Flight Testing Handbook, stated, "…test flying an aircraft is a critical undertaking, which should be approached with thorough planning, skill, and common sense." The handbook provided guidance on preparing a plan for each phase of the amateur-built airplane's production, including preparing for the airworthiness inspection, weight and balance, taxi test, flight testing, and emergency procedures. The suggested flight testing regimen was separated into 10-hour segments for the 40-plus hour flight testing requirement. Suggested guidelines for the experience level of the test pilot for the recently-completed amateur-built airplane were also provided, and included that pilots should be, "Rated, current, and competent in the same category and class as the aircraft being tested."
The pilot's improper adjustment of the propeller blade angle, which resulted in inadequate engine thrust, and his decision to continue the takeoff despite the excessively long takeoff roll.
Source: NTSB Aviation Accident Database
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