On July 26, 1998, about 1800 Eastern Daylight Time, a homebuilt Revolution Mini-500 helicopter, N805JJ, was substantially damaged during a forced landing at Yost Airport (32PA), Shermans Dale, Pennsylvania. The certificated private pilot was not injured. Visual meteorological conditions prevailed at the time of the accident. No flight plan was filed for the personal flight conducted under 14 CFR Part 91.

According to the pilot's written statement, after about 45 minutes of flight, he entered the traffic pattern at his destination, and descended during both the base leg and the final approach. While on the final approach, at 20 to 30 feet of altitude, the engine "stopped dead ... no sputtering, no sign, just nothing." The helicopter landed hard, the left skid collapsed, the main rotor struck the tail boom, and the helicopter rolled over on its left side.

According to a Federal Aviation Administration (FAA) Inspector, the fuel tank was approximately 1/3 full, and there was fuel in the glass bulb along the fuel line. There was sufficient engine oil in the oil tank and the throttle linkage was intact.

In a supplemental statement, the pilot wrote: "After discussions with Revolution Helicopter and other Mini-500 owners, the most likely cause of engine failure is fuel starvation due to a bad main jet, needle jet combination. I had recently installed the Power Enhancement Package, which included a new needle (11K2), a new needle jet (2.76), and a new main jet (1.70). This combination caused the EGT to be below operating minimums, so I reduced the size of the main jet in order to lean the mixture sufficiently to produce suitable EGTs. My final jet combination was a 2.72 needle jet and a 1.52 main jet. I had flown approximately 8 hours with that combination without a problem. The problem occurs when it is necessary to go from half throttle to full throttle rapidly. The 1.52 main jet is too restrictive to allow enough fuel through, quickly enough, to allow the engine to go to full throttle. It is like filling a syringe by pulling back the plunger. As long as you pull the plunger back slowly and evenly, the syringe fills up fine. If you pull the plunger back quickly, the syringe fills with air.

In my particular situation, I was descending on final approach at less than half throttle. When I got close enough to the ground to begin adding collective and throttle in order to stop the descent, I added throttle too quickly...The engine simply could not get enough fuel, fast enough, to get full throttle, and the engine stalled."

On July 27, 1995, a Revolution Helicopter Corporation-owned Mini-500 sustained substantial damage when it experienced a total loss of engine power during a demonstration flight. According to the Safety Board's Factual Report, the company owner stated that re-jetting of the carburetor had been performed in an attempt to bring down gauge readings when a new rotor/engine rpm instrument and a new exhaust gas temperature gauge were installed. The company owner attributed the engine seizure to the re-jetting.

A review of accidents compiled from the National Transportation Safety Board database revealed that, in 1997 and 1998, there were 23 Mini-500 accidents. Within that list, 11 involved a loss of engine power.

The accident Mini-500 used a Rotax 582 UL DCDI engine. In the beginning of the operator's manual, it stated: "Danger! This engine, by its design, is subject to sudden stoppage! Engine stoppage can result in crash landings. Such crash landings can lead to serious bodily injury or death. Never fly the aircraft equipped with this engine at locations, airspeeds, altitudes, or other circumstances from which a successful no-power landing cannot be made, after sudden engine stoppage."

The operator's manual also stated: "Warning! This is not a certificated engine. It has not received any safety or durability testing, and conforms to no aircraft standards. It is for use in experimental, uncertificated aircraft and vehicles only in which an engine failure will not compromise safety. User assumes all risk of use, and acknowledges by his use that he knows this engine is subject to sudden stoppage."

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