NTSB Factual Report

On April 17, 2017, about 1341 central daylight time, an experimental, amateur-built Loomis Xenon 4 gyroplane, N912XV, sustained substantial damage after takeoff from the Knoxville Municipal Airport (OXV), Knoxville, Iowa. The gyroplane climbed to about 500 ft above ground level when it experienced a partial loss of power, and during the forced landing, hit a powerline and landed in a ditch. The sport pilot and pilot rated passenger were not injured. The gyroplane was owned and operated by the pilot under the provisions of the 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed for the flight which was not on a flight plan. The flight was departing OXV on a local flight.

The pilot reported that on the day of the accident, he and his son had flown from Knoxville, Iowa, to Newton, Iowa, and back. The flight was about 1-hour long. After they landed, he checked the fuel and it showed 10 gallons remaining. He was about to refuel the gyroplane when the accident passenger came over to the aircraft and talked about getting a ride. Since the pilot's brother had already offered to give the passenger a ride, the pilot offered to go for a 10-minute flight. He stated that the passenger weighed about 220 lbs and he weighed 165 lbs. With 10 gallons of fuel on board, he stated that they were within the weight and balance limits of the aircraft.

The pilot taxied to the end of the runway and did a full-length departure. He stated that the taxi, runup, takeoff, and climb to 500 ft above ground level (agl) were normal. The engine was running fine. He had planned to climb to 1,000 ft agl, circle around, and come back to the airport. However, while continuing to climb through about 500 ft agl, the gyroplane stopped climbing and started to descend. He didn't remember hearing any change to the sound of the engine and he thought the engine was still running, but he was aware that the gyroplane wasn't climbing anymore. He checked the altimeter and confirmed that they were in a descent. He started to turn back to the airport but realized he couldn't make it back and tried to land in a field. He saw that he would not clear the powerlines, so he turned sharply, but the gyroplane hit the powerline and crashed on the side of the ditch. He turned the engine and fuel off and he and the passenger climbed out the aircraft. A small grass fire had started in the ditch by the fallen powerline about 20 yards from the gyroplane and it was quickly extinguished; it did not affect the gyroplane wreckage.

The pilot rated passenger reported that the takeoff was uneventful. He stated that during the initial climb, he heard a change in the sound of the engine, like a decrease in engine RPMs. The pilot told him that they were losing power as he was attempting to troubleshoot the problem. The pilot turned to an open field to the right side of the gyroplane but was unable to avoid hitting the powerline. He reported that it was about 10 to 15 seconds from the time of the loss of power until impact. The accident site was located about 800 ft south of the departure end of runway 15.

The gyroplane wreckage was transported back to the airport. The next day Federal Aviation Administration (FAA) inspectors examined the aircraft. The engine appeared to be operational, so they decided to try start the engine. It started without hesitation and it was run at idle power, but only for a brief time, since the propeller was broken, and it created a lot of vibration.

The Xenon 4 Executive model gyroplane was a one-piece monocoque structure made of carbon composite with a fixed tricycle landing gear arrangement. It was a two-seat gyroplane with a maximum takeoff weight of 1,234 lbs. The kit was manufactured by Celier Aviation and it was registered as an experimental, amateur-built gyroplane in the United States. The engine was a turbocharged 135-horsepower Rotax 912 ULST that was modified by Celier Aviation from the 100-horsepower Rotax 912 ULS engine. Two metal tail booms exited the rear of the fuselage and had vertical stabilizers and rudders mounted to each boom. A horizontal stabilizer and elevator were mounted between the vertical stabilizers. The control surfaces were also of composite construction. A metal mast was affixed to the fuselage structure, on which the control head with the lifting rotor was mounted. The two-blade rotor had a metal structure with blades made from drawn aluminum.

The brother of the accident pilot stated that the dealer for the gyroplane was in Dubuque, Iowa, which was about 100 miles from his home. He stated that he built and assembled the gyroplane from the manufactured kit, and that it took about four, 12-hour days to complete building the gyroplane. He stated that the maximum takeoff weight of the gyroplane was 1,320 lbs. The gyrocopter was issued a special airworthiness certificate on February 16, 2016. He stated that the kit manufacturer provided the owners a Rotax 912 ULS maintenance manual for the engine, but they did not provide a maintenance manual for the modified, turbocharged Rotax 912 ULST engine. The pilot's operator manual for the gyroplane did not provide any information concerning the operation of the turbocharger. The aircraft logbook did not indicate that an annual condition inspection had been performed before the accident occurred.

Figure 1 View of the Celier Aviation Modified Rotax 912 ULST Engine

The brother of the pilot stated that the gyroplane operated flawlessly until they started having carburetor problems with flooding. The engine logbook entry dated January 1, 2017, indicated that the gyroplane's hour meter read 266.2 hours. The logbook entry indicated that the carburetors' floats were changed, and new floats were installed. An aviation mechanic familiar with Rotax engines installed the new carburetor floats. The mechanic synchronized the carburetors and it seemed to fix the flooding problem. The mechanic was a trained Rotax mechanic, but he was unfamiliar with the modified turbocharger installation and did not know how to maintain or repair it.

The brother of the pilot stated that the gyroplane continued to have problems developing full power. He stated that the engine would develop about 3,500 RPMs instead of developing full power at 5,200 to 5,300 RPMs. The dealer suggested he try removing the orifice (manifold pressure probe) and clean it of any oil, grease or debris. He removed the orifice and cleaned it. However, there was no index on the orifice, so he reinstalled it in the same position as best as he could determine. By trial and error, he would loosen the lock nut on the orifice and turn it 1/16-inch one way or the other until the engine developed full power at 5,300 RPMs. He stated that the engine would develop full power for a while and then it would revert to only producing about 3,500 RPMs. Then he would readjust the orifice until he got it to produce full power again. He stated that he repeated this process about 5 or 6 times, and the gyroplane was flown about 30 more hours. He compared the engine problem to when a "choke" lever is pulled when an engine is operating - it loses power and can't develop enough power for operation.

Figure 2 Manifold Pressure Probe

The pilot wrote in his pilot's logbook on April 7, 2017, "Not running right – missed at high RPM." The pilot did not fly that day and entered 0 hours flown in his logbook. The brother of the pilot reported that he changed the orientation of the manifold pressure probe again until it produced full power. He reported that the gyroplane operated 7.9 hours without any anomalies before the accident occurred on April 17th.

The brother of the pilot reported that he was not sure what the TURBO knob located on the center pedestal controlled or what its function was. He said he turned it occasionally, but it didn't make any difference in the turbo boost. He said it would make a change to the turbo manifold pressure gauge of about 1/10th degree. He said that when the engine developed 5,300 RPMs at full power, the manifold pressure gauge would indicate about 40" Hg. When in cruise flight, the gauge would indicate 10 – 15" Hg. The accident pilot also stated that he did not know what the function of the TURBO knob was, and that he would not move it.

The dealer for the experimental Xenon 4 reported that the gyroplane met the "51%" rule for an experimental, amateur-built gyroplane. He stated that the aircraft's rotor is test flown to ensure proper balance and tracking of the rotor head. It was then disassembled and shipped with the rest of the gyroplane kit to the United States. The owner/builder then built and assembled the gyroplane which complied with the "51%" rule.

The dealer reported that the manifold pressure probe is located on the aluminum tube that is between the intercooler and the airbox. It senses the turbocharged air pressure and provides vacuum to the top of the carburetors' diaphragm which then schedules fuel for the carburetors. The greater the turbocharged air pressure, more fuel is required. He stated that the position of the orifice is critical and it's a very sensitive adjustment. If it moves or becomes obstructed in any way, then the pressure schedule to the carburetors is adversely affected and the engine fails to produce the required power. He stated that the Turbo adjustment knob on the center pedestal is for adding boost power. The knob is connected to the wastegate via a transparent plastic hose. It bleeds off turbo vacuum pressure which overcomes the turbo springs, allowing for more boost power. He stated that kit manufacturer did not provide operating or maintenance manuals for the gyroplane. There were no procedures provided about how to operate or maintain the turbocharged Rotax 912 ULST.

NTSB Probable Cause

A partial loss of engine power for reasons that could not be determined based on the available information. Contributing to the accident was the failure of the owners to obtain proper materials regarding the operation and maintenance of the engine.