AGUA DULCE, CA, USA
N501GM
MITTEER MINI 500
The pilot of the recently completed, kit-built helicopter, stated that the engine stopped abruptly about 150 feet above helipad elevation as he was on base leg for landing. A hard landing resulted from an unsuccessful autorotation. Examination of the helicopter revealed that the size of the metering jet installed in both carburetors by the owner/pilot was too small, and that the fuel metering pin in both carburetors was improperly set so as to create an excessively lean fuel/air mixture, which resulted in loss of engine power. The pilot reported having 50 hours total helicopter flight time and that he last practiced autorotations 22 years prior to the accident. A revised aircraft assembly manual, which added a discussion of fuel jets and metering pins, was offered to holders of the earlier manual at a reduced price; however, the owner/builder did not purchase it. An article in the manufacture's newsletter, again discussing the importance of this subject, was sent to the owner/builder's address of record.
On July 31, 1997, at 1945 hours Pacific daylight time, an experimental (amateur built) Mitteer Mini 500 helicopter, N501GM, was substantially damaged when it collided with terrain while on landing approach to a private helipad at Agua Dulce, California. The commercial pilot was seriously injured. Visual meteorological conditions prevailed for the personal flight. The recently completed helicopter departed from the helipad about 1940. According to the pilot's brother, the pilot related from his hospital bed that the engine stopped abruptly about 150 feet above helipad level as he was on base leg for landing. Because previous approaches had been at too steep an angle, the pilot was deliberately flying a flatter and slower approach, which, together with his low altitude when the engine failed and lack of a suitable landing site, made his autorotation unsuccessful. According to inspectors from the Van Nuys Flight Standards District Office, the aircraft impacted on a two-lane asphalt road about 1/8 mile from the helipad in a valley about 100 feet below the helipad elevation. Terrain slopes upward about 45 degrees on one side of the road and there are power transmission lines on the other side of the road, however, the helicopter contacted neither prior to impacting on the roadway. The impact bent both landing skids outward and the belly of the fuselage contacted the pavement. The pilot's seat structure exhibited compression failure with more collapse on the left side than the right side. The two rotor blades had minor damage on the lower surface of the tips. After impact, the aircraft rotated 90 degrees to the right and came to rest about 10 feet away from the impact mark, resting on its left side. According to the inspector, no airworthiness certificate or operating limitations had been issued to the builder/pilot by the Federal Aviation Administration. The recording hour meter in the aircraft indicated 8.4 total hours, however, the pilot told his brother that he had operated the aircraft more than those hours. The pilot's logbook indicated total operating time since new, including ground run time, of 14.8 hours. The first entry was about a month before the accident. The last entry in the logbook, for the previous flight, indicates that the pilot changed the fuel metering jets in the carburetors to "150" size. The pilot reported having 50 hours total helicopter flight time, with 18 hours in the previous 60 days. In a telephone conversation with the Safety Board in December, 1997, the pilot said that he received his helicopter training in 1975 in a Bell 47 helicopter, and that was the last time he practiced an autorotation to landing. In June, 1997, prior to first flying his Mini 500, he took 2 hours of dual instruction in a Robinson R-22, but did not perform any autorotation practice. Representatives of the company which manufactures the parts kit for the helicopter, examined the aircraft and determined that the size of the metering jet installed in both carburetors by the owner/pilot was too small, and that the fuel metering pin in both carburetors was improperly set so as to create an excessively lean fuel/air mixture in the engine. Examination of the aft piston of the two cylinder engine through the exhaust port showed scoring on the sides of the piston and evidence of "hot seizure." A manufacture's bulletin on the subject of sizing metering jets and metering pins in the carburetor to control exhaust gas temperature was issued on May 7, 1996, the same day the kit was shipped to the manufacture's dealer. The dealer signed and returned a receipt for the bulletin to the manufacturer who placed it in the file for the aircraft serial number. The kit was sold to the builder/pilot on January 13, 1997, and there is no record whether there was a copy of the service bulletin with the kit. An article in the manufacture's newsletter of March, 1997, discussed the importance of this subject again. According to the kit manufacturer, the newsletter was mailed to the builder/pilot's address of record, which was his business address. A revised aircraft assembly manual which added a discussion of fuel jets and metering pins was offered to holders of the earlier manual at a reduced price. The owner/builder did not purchase the revised manual.
failure of the owner/builder to obtain and comply with service literature from the kit manufacturer, which resulted in improper setting of the carburetor fuel mixture and led to loss of engine power. An additional cause was the pilot's failure to successfully autorotate the helicopter to an emergency landing. The pilot's lack of total experience in the type helicopter and lack of recent experience in performing autorotations were related factors.
Source: NTSB Aviation Accident Database
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