GETTYSBURG, OH, USA
N727EB
Bihn MINI 500
The homebuilt Mini 500 helicopter was in level flight about 900 to 1200 feet, when the engine sounds stopped. The helicopter's nose dropped, and one main rotor blade struck the tailboom and separated from the rotor head. The helicopter descended and struck the ground 90 degrees nose down. Examination of the non-certificated 2 cycle Rotax engine did not reveal a reason for the power loss. The engine manufacturer published the maximum continuous RPM as 6,500. Other builders reported that when the helicopter's rotor RPM was operated at the top of the green arc, the engine operated about 6,700 RPM. The NTSB database revealed 23 Mini-500 accidents in 1997 and 1998. Twelve of those involved a loss of engine power. The Rotax operator's manual stated, '...This engine by design is subject to sudden stoppage...Never fly the aircraft equipped with this engine at locations, airspeeds, altitudes...from which a successful no-power landing cannot be made...'
HISTORY OF FLIGHT On December 19, 1997, about 1450 eastern standard time, a homebuilt Mini 500, a helicopter, N727EB, was destroyed during an uncontrolled descent and collision with terrain near Gettysburg, Ohio. The certificated airline transport pilot, with a private pilot helicopter rating, was fatally injured. Visual meteorological conditions prevailed for the personal flight that originated at the Phillipsburg Airport, Phillipsburg, Ohio, about 1415. No flight plan had been filed for the local flight conducted under 14 CFR Part 91. According to witnesses, the helicopter was observed in level cruise flight, at 900 to 1,200 feet above the ground, when they heard the engine noise of the helicopter decrease. This was followed by the sound of two "pops or bangs." Witnesses observed the tail of the helicopter raise up, and an object depart from the helicopter. The helicopter then descended below tree level where it struck the ground nose down. According to one witness: "...I heard a two stroke high pitch engine and heard the rotor blades. I'm a pilot myself and knew from the sound what it was. I went out to see the helicopter and saw it fly past about 1/4 mi away to the east. When it had proceeded aprox 1/4 away behind some trees, I heard the engine stop. I could hear the rotors but no engine noise. Then I heard two loud noise's similar to the sound a shotgun makes. Then I saw something bounce out in a field..." PERSONNEL INFORMATION The pilot flew for a commercial airline and possessed an airline transport pilot certificate. He had logged in excess of 10,000 flight hours in airplanes. His most recent Federal Aviation Administration (FAA) First Class Medical Certificate was issued on September 17, 1997. According to a log book which contained helicopter flights only, the pilot began helicopter training on June 10, 1996. The pilot obtained his private pilot helicopter certificate on July 4, 1997. He had accumulated 59.9 hours in helicopters, of which 15.4 hours were logged as pilot-in-command. All of his training had been conducted in the Robinson R-22. There were no other entries in the log book. Based upon maintenance records and interviews, the pilot's next helicopter flights were those in N727EB, after November 17, 1997. At the time of the accident, it was estimated that he had logged about 10 hours of hover, and 2 hours of flight, in N727EB. AIRCRAFT INFORMATION The pilot purchased the helicopter as a kit, from Revolution Helicopter Corporation, Inc., Excelsior Springs, Missouri. According to a maintenance logbook entry, the pilot signed off the engine break-in, at a Hobbs time of 1.5 hours, on September 25, 1997. He further signed off that he had inspected the helicopter for issuance of an experimental airworthiness certificate on November 17, 1997. Also on November 17, 1997, at a Hobbs time of 1.7 hours, a special airworthiness certificate was signed off by a Federal Aviation Administration Inspector. On November 23, 1997, at a Hobbs time of 4.1 hours, main and tailrotor rigging and tracking were signed off by a person who possessed an airframe and powerplant certificate. WRECKAGE AND IMPACT INFORMATION The helicopter wreckage was examined by Federal Aviation Administration (FAA) Inspectors, and two individuals with knowledge of Mini 500's, at the accident site. According to the FAA Inspectors, the wreckage came to rest in an open field, 90 degrees nose down, with the forward ends of the skids imbedded about 1 foot into the ground. One of the FAA Inspectors stated: "One main rotor blade was absent from the accident site and was found approximately 900 ft from the main crash site. The blade was bent at an approximate 20 degree angle and the trailing edge was split open...Examination of the tail boom revealed that the horizontal and vertical tail plane had been severed/broken from boom approximately 24 inches from outboard end of tail boom. The remaining section of the tail boom had a severe dent in it, indicating that it had been struck by a main rotor blade." The Inspector's report also stated that the helicopter was equipped with a Rotax 582 engine. During the examination of the engine, the cylinder head was removed, and the spark plugs "looked normal." The exhaust manifold was removed in order to inspect the cylinder walls for condition and evidence of any damage. The report stated, "No damage was noted." The engine was rotated by hand using the starter flywheel, and the engine "appeared to rotate normally." The report further stated, "We were unable to determine if engine was running at time of impact." MEDICAL AND PATHOLOGICAL INFORMATION An autopsy was performed on the pilot, on December 20, 1997, by Dr. David M. Smith, of the Montgomery County Coroner's Office, Ohio. The toxicological testing report from the FAA Toxicology Accident Research Laboratory, Oklahoma City, Oklahoma, revealed negative for drugs and alcohol. ADDITIONAL INFORMATION According to a person who had discussions with the pilot: "...[the pilot said] I tried an autorotation yesterday and didn't like it. (12/13/97) I started at about 800 ft. AGL in the pattern and came back off the power. Man was it squirrelly. It came down too fast so I came back in on the power right away and recovered. I will have to do many more before I feel good about this thing. I asked him what he could [do] different? He said that he found out that even though the nose goes down when you cut the power, that he will need to move the nose forward even more to keep the rotor speed up..." Another pilot/owner stated that he had logged about 14 hours on a Mini 500 that he had built. While in cruise flight, at 600 feet above the ground, his "engine quit." He then autorotated to an open field. During an inspection of the helicopter, he observed a "small dent in the top of my tail-boom. Pulling down on the rotor blades I found out that the dent did match the tip of the blades." Another pilot/builder of a Mini 500 who had about 250 hours experience in his helicopter was interviewed. He stated that when the rotor RPM was at the top of the green on the tachometer, the engine was running about 6,700 RPM. In discussion with other builders of the Mini 500, they also confirmed the engine ran about 6,700 RPM during continuous operations. According to the Mini-500 Aircraft Assembly and Maintenance Manual (Section 1, page 3), the Rotax 582 was a water cooled, 67 horsepower engine. No RPM was listed. The same page also provided the main rotor speed. It stated, "Blade RPM...546 @100% RPM" The Mini-500 Pilot's Operating Handbook (POH) listed limitations on page 4 and 5. The POH explained that green instrument markings were the normal operating range, yellow instrument markings were the cautionary operating range, and red instrument markings were the maximum operating limits. There were no time frames listed with the color code explanations. Excerpts of the limitations were as follows: Rotor RPM - Green...............96% to 104% Upper yellow....104% to 110% Upper red line..110% Engine RPM-Green................98% to 102% Red line............110% The Operator's Manual for the 2 Cycle Rotax 582, published by Bombardier-Rotax GmbH, listed the power output for the 582 as, "48kW (64,4 hp SAE) at 6500 1/min." A representative from Rotax stated that engine limitations for the 582 were 6,500 RPM continuous, and 6,800 RPM for a maximum of 5 minutes. On the inside page of the Rotax 582 Operator's Manual, a warning was published. It stated: "This is not a certificated aircraft 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." The same page also listed a danger note. It stated: "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 these engine at locations, airspeeds, altitudes, or other circumstances from which a successful no-power landing cannot be made, after sudden engine stoppage." 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, 12 involved a loss of engine power. The wreckage was released on January 16, 1998, to the brother of the pilot.
A loss of engine power for undetermined reasons, followed by the main rotor striking the tailboom, which resulted in the separation of a main rotor blade.
Source: NTSB Aviation Accident Database
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