Grain Valley, MO, USA
N484XB
BECKER ELMER L STOL CH 750
Data from the onboard avionics device revealed that, after conducting a touch-and-go landing, the amateur-built airplane immediately began a low-speed, high-pitch-angle climb. The airplane's airspeed began to decrease as the airplane climbed to about 47 ft above ground level and then began rolling left; the recording then ended. Witnesses reported observing the airplane roll, descend, and impact terrain. The data and the witness statements are consistent with the airplane having experienced an aerodynamic stall. A postaccident examination of the composite propeller found that it did not display signatures of rotation during impact, consistent with a total loss of engine power. The engine manufacturer's initial installation used a single battery with a series of breakers and relays to provide power to the engine components and other equipment. This design was subsequently replaced by a dual-battery design that incorporated a simpler wiring harness. The airplane was originally wired for a single-battery operation, and a second battery was subsequently added. However, the simpler wiring harness was not used; instead the electrical path from the alternator to the alternator sense wire used a complex series of fuses to provide power to the components; one of these fuses was found open, which is indicative of an electrical power failure and would have led to the loss of engine power. Although the onboard avionics device did not record the airplane's loss of engine power, descent, or impact with terrain, the interruption of the recorded data likely resulted from the electrical failure. The pilot had removed the airplane's slats 9 days before the accident; the accident flight was the pilot's first flight in the airplane with the new configuration. According to the kit designer, the airplane was not designed to fly with the slats removed because it would result in a higher stall speed with a distinct stall break and roll if the flight was not coordinated. In addition, the pilot had recently resumed flying after not having flown in about 45 years. Although he had received 2 hours of dual instruction about 2 months before the accident, after a test flight in a company airplane, another pilot assessed the accident pilot's piloting skills as poor and advised him to obtain further instruction; however, the accident pilot did not do so. Given his lack of recent flight experience, he was likely not properly prepared for how to respond to a loss of engine power and the subsequent stall.
On August 19, 2014, about 1400 central daylight time, a kit-built Zenith STOL CH 750 airplane, N484XB, collided with terrain while attempting to depart the East Kansas City Airport (3GV), Grain Valley, Missouri. The commercial pilot was seriously injured and the airplane was substantially damaged. The airplane was registered to and operated by a private individual under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed for the flight, which operated without a flight plan. The local flight departed 3GV about 1230.While conducting touch and go landings the airplane was observed by witnesses to climb to about 100 feet above ground level before the airplane rolled and quickly descended. The airplane collided with the ground and substantial damage was sustained to the airplane's fuselage and wings. A postaccident examination of the airplane and engine found only impact damage to the composite propeller. The airplane was a kit-built Zodiac STOL CH 750 powered by a 110 horsepower Viking Aircraft Engines 110 engine. The airplane was issued a special airworthiness certificate on June 25, 2014, and the airplane was still in Phase 1 testing. On August 10, 2014, the pilot removed the airplane's leading edge slats and did not fly the airplane until August 19. The pilot's son stated that the pilot removed the slats in an effort to make the airplane fly more like a Cessna airplane. The airplane was equipped with a Dynon Skyview SV-D1000 multi-function display. Data recorded in the device was downloaded by the National Transportation Safety Board Laboratories, Washington, D.C. Data retrieved from the device contained the accident flight. Data recorded the flight's departure at 1230 and recorded the flight as the airplane made a 180 degree turn to the east and climbed to 5,225 feet mean sea level (msl). The data did not contain any stall maneuvers during this portion of the flight. The airplane then descended and headed back towards 3GV. The flight path was consistent with seven touch and go landings. The first six landings occurred at airspeeds between 42 and 52 knots. On the seventh landing, the airplane landed at 35 knots and accelerated to 45 knots on the runway before the airplane lifted off and began climbing. The airplane was pitched up between 15-20° nose high and rolled left between 5-10°. The airspeed began to decrease as the airplane climbed to about 47 feet above ground level (agl). The airplane slowed to 39 knots and then began to increase as the airplane remained level about 47 feet agl. The last recorded information showed the airplane at 982 feet msl (about 47 feet agl), airspeed at 44 knots, 12° of pitch, and 7° degrees of left roll. At that time, the engine was operating at 4,867 rpm with a fuel flow of 4.6 gallon per hour. The data ended prior to the airplane's descent and impact with terrain. According to a representative of Viking Aircraft Engines, electrical power is required to keep the fuel pump, ECU, and engine operational. Early installations used a single-battery concept and a series of breakers and relays to provide the necessary power to the engine components and other equipment. Subsequently, a dual battery design incorporated a simpler wiring harness where one battery would provide power to the engine components and a second battery served as a backup. If the airplane is wired as recommended, the alternator enable signal wire will continue to be powered by the alternator through the key switch in the "on" position. If the alternator stays operational, the batteries are not needed to supply electrical current for engine operation. The current wiring diagram shows that the alternator enable signal wire is powered by either the alternator through a 60 Ampere (A) and 10A fuse or the batteries through the 10A fuse and the ignition switch. The ECU is powered directly by either battery or alternator. No other components appeared in alternator enable wire circuit. The accident airplane had been wired for a single battery operation and a second battery was subsequently added. However, the wiring was not simplified with the addition of the second battery. The path from the alternator to the alternator sense wire went through a 60A resettable High Ampere (Hi-Amp) Buss fuse, a 60A copper strip fuse, a 100A resettable Hi-Amp Buss fuse, a 50A resettable Hi-Amp Buss fuse, a 2A SAE fuse, a relay and a starter switch with off, on, and start positions. The alternator enable signal wire was attached between the "on" position pole and the alternator enable pin on the alternator. Each of the resettable fuses and the copper fuse had several other wires that fed other airplane and engine components. A postaccident examination of the airplane found the 100A resettable Hi-Amp Buss fuse was open and reset when pushed by the investigator. There was mechanical damage around the reset arm and is could not be determined when the fuse opened. No other fuses were found open. A review of the pilot's log book displayed that the pilot starting flying in 1968 and stopped flying in 1969 having logged 197.4 hours of total time and 91 hours of dual instruction. The pilot resumed flying on June 12, 2014, with 2 hours of dual instruction and the completion of a flight review. The pilot flew approximately 5.1 hours in the accident airplane between July 3, 2014, and August 10, 2014. The pilot' next flight was the accident flight. Prior to the construction of the accident airplane, the pilot had flown with a representative from Zenith to test fly a company airplane. The Zenith pilot assessed that the accident's pilot flying skills were poor and advised him to obtain further training. According to the representative from Zenith Aircraft, the STOL 750 is not intended to be flown with the slats removed. The wing airfoil and horizontal stabilizer/elevator are different from the non-STOL CH750. As a normally configured STOL CH750 airplane slowed to 40 mph, the airplane would mush and a high sink rate could develop unless a substantial amount of power was added. The representative had no experience flying the airplane without the slats. He estimated that the stall speed would be higher and there would be a distinct stall break. Any uncoordinated flight would result in a roll. He further stated that the non-STOL CH750's stall speed is about 42-43 mph with a distinct stall break and the airplane will roll if not coordinated. The representative of Viking Aircraft Engines stated that he has flown his STOL CH750 with the slats removed. The stall speed was higher with a distinct stall break and roll. A representative from Dynon Avionics stated that external electrical power is required to maintain the data log; any interruption to the power would result in the log ending.
The pilot’s failure to maintain airplane control during a low-speed, high-pitch climb after the airplane experienced a loss of electrical power and subsequent total loss of engine power, which resulted in an aerodynamic stall. Contributing to the accident was the airplane’s modified electrical system and the pilot’s failure to obtain adequate familiarization and experience in the airplane with the recent slat-removed configuration.
Source: NTSB Aviation Accident Database
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