OSHKOSH, WI, USA
N500ZZ
REVOLUTION HELICOPTER MINI-500
The amateur-built helicopter was conducting a demonstration flight during the annual EAA convention. During the first flight after re-jetting of the carburetor, the helicopter experienced a total loss of engine power. During the autorotation into a crop field, the helicopter was substantially damaged when the skid shoes caught in the terrain, failing the left skid and fracturing the shoe on that skid. Subsequent examination of the engine revealed that the rear piston had seized in the cylinder. The owner of the company which produces the helicopter stated that the re-jetting of the carburetor was made in an attempt to achieve what were thought to be correct readings in main rotor RPM and EGT after replacement of both gauges. The company owner attributed the piston seizure to the re-jetting. The skid shoes were new and had been tested only on concrete. The owner said that the design contributed to the damage to the helicopter.
HISTORY OF FLIGHT On July 27, 1995, at 0930 central daylight time, an amateur built Revolution Helicopter Mini-500, N500ZZ, registered to Revolution Helicopter Corp. of Ecelsior Springs, Missouri, and piloted by a commercial helicopter pilot, experienced a total loss of engine power while in cruise flight. During an auto rotational (forced) landing, one-half mile west of Wittman Regional Airport, Oshkosh, Wisconsin, the helicopter sustained substantial damage. The pilot reported no injuries. The local 14 CFR Part 91 flight was operating in visual meteorological conditions. No flight plan was on file. The flight departed at 0920. The accident occurred during the annual Experimental Aircraft Association's convention. The helicopter was conducting a demonstration flight in the vicinity of the airport at Oshkosh, Wisconsin. PERSONAL INFORMATION The pilot had obtained approximately 100 hours flight time in this type of helicopter, at the time of the accident. This was the first flight of the day. AIRCRAFT INFORMATION The helicopter had accumulated 210 hours time in service at the time of the accident with less than one hour since inspection and maintenance to the carburetor which included changing the jetting. WRECKAGE AND IMPACT INFORMATION The helicopter impacted the terrain during an forced landing in an open field approximately one-half mile west of Wittman Regional Airport, Oshkosh, Wisconsin. There were two ground scars consistent with the size and shape of the skids running westerly from the first visible impact mark to the wreckage. The left skid was broken away from its mounting. The tail boom was lying to the north of the main wreckage and exhibited sharp fractures at the broken end. The tail rotor blades were bent. The main rotor blades were bent and broken and one had red paint on it similar to the color of the tail boom. Subsequent examination of the engine found that the rear piston was seized in the cylinder. The owner of the company producing the helicopter said that two changes to the helicopter just prior to the flight were of concern. He stated that a new rotor/engine RPM instrument was installed at the same time as a new exhaust gas temperature (EGT) gauge. He said that prior to the installation of these gauges that the helicopter was operating without incident; however after reading the indications on these new instruments re-jetting of the carburetor was done in an attempt to bring the readings within gauge limits. The owner attributed the seizure to the previous accomplished re-jetting. He said that at the same time a new set of skid shoes were installed on the skids of the helicopter and testing was done on concrete only. When an autorotational landing was conducted in a crop field the new skid shoes dug in and stopped the helicopter in a short distance, failing the left skid and fracturing the skid shoe on that skid. ADDITIONAL INFORMATION The NTSB did not exercise its right to retain custody of the wreckage. When the on scene investigation was complete the wreckage was removed and retained by the owner. Party to the investigation was the Federal Aviation Administration, Flight Standards District Office, Milwaukee, Wisconsin.
the inadequate design of the helicopter skid shoes. Factors related to the accident were: false indications of rotor rpm and EGT which led to seizure of the piston.
Source: NTSB Aviation Accident Database
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