MIDLAND, VA, USA
N500GH
Armbruster MINI-500
The pilot/owner was flying his amateur-built helicopter and crashed in a wooded area. Examination of the helicopter revealed that the non-certificated 2-cycle engine had experienced a power loss due to a 'cold seizure.' About 18 Hobbs meter hours prior to the accident the pilot had replaced pistons, rings, wrist pins, rod bearings, thermostat and head O-rings. Metallurgical examination of the PTO cylinder walls revealed deposits from the side (piston skirt) of the accident PTO piston and a previous PTO piston, indicative of a prior cold seizure event. Although the kit helicopter was built according to plans, the engine manufacturer did not recommend several of the engine modifications found on the accident helicopter. Additionally, the engine manufacturer did not recommend the installation of this model engine in the helicopter and published the following warning with the engine manual: 'This engine, by its design is subject to sudden stoppage. Engine stoppage can result in crash landings, forced landings or no power landings. Such crash landings can lead to serious bodily injury or death.'
HISTORY OF FLIGHT On November 29, 1998, about 1515 Eastern Standard Time, an amateur-built Mini-500 helicopter, N500GH, was destroyed during a collision with trees and terrain near Midland, Virginia. The certificated private pilot/owner/builder was fatally injured. Visual meteorological conditions prevailed for the local flight that originated from the Manassas Airport (HEF), Manassas, Virginia. No flight plan was filed for the personal flight conducted under 14 CFR Part 91. A family member reported the pilot missing after he did not return from a 45-minute local flight on November 29, 1998. Tower personnel at HEF recorded the helicopter took off at 1400, and witness reports indicated that the helicopter was near Leesburg Airport (JYO), Leesburg, Virginia, about 1430, and near Nokesville, Virginia, about 1500, on the day of the accident. A search conducted by the Civil Air Patrol located the helicopter on December 2, 1998, about 1530, in a wooded area, approximately 1/4 mile north/northeast of the Warrenton-Fauquier Airport (W66), Warrenton, Virginia. The accident occurred during daylight hours at approximately 38 degrees 35 minutes north latitude and 077 degrees 41 minutes west longitude. PERSONNEL INFORMATION The pilot held a private pilot certificate with ratings for airplane single engine land, instrument airplane, and rotorcraft/helicopter. He held a repairman certificate for the Mini-500, issued on May 27, 1997, with limitations for the accident helicopter only. The pilot was issued a third class medical certificate on July 23, 1997. He reported 1,105 hours of total flight experience on that date. AIRCRAFT INFORMATION The helicopter was built from a kit purchased from the Revolution Helicopter Corporation, and was issued an experimental airworthiness certificate on July 27, 1996. The helicopter was a single seat, lightweight two-bladed conventional rotorcraft utilizing a semi-rigid teetering, underslung main rotor system and a two bladed free-to-teeter tailrotor for anti-torque control. The flight controls were push-pull tubes using a triple gimbal for mainrotor system control. The airframe was welded steel tubing covered by fiberglass fairings. Drive belts accomplished the engine-to-transmission drive. The helicopter used two fixed skids for structural ground support, and was powered by a Rotax 582UL 2-cycle liquid cooled powerplant. The main rotor blades were symmetrical airfoils with a constant 8-degree twist and were 9 feet long with an 8-inch cord. The rotor disk diameter was 19 feet 2 inches. The blades had an extruded aluminum leading edge spar, a machined foam core, and a fiberglass outer skin. The tail rotor blades had an aluminum spar and were wrapped in aluminum skins. According to a small notebook found in the pilot's hangar, the last annual inspection was completed on May 3, 1998, at 175.6 aircraft hours. The helicopter's Hobbs meter indicated a total flight time of 218.7 hours at the time of the accident. The engine logbook indicated that in August 1998, at 200.4 hours on the Hobbs meter, the owner replaced pistons, rings, wrist pins, rod bearings, thermostat, and head o-rings. WRECKAGE AND IMPACT INFORMATION The wreckage was examined at the site on December 3, 1998, and all major components were accounted for at the scene. Tree limbs measuring 4 to 6 inches in diameter were cut horizontally and found near the base of a 50-foot tree (initial impact point). The main wreckage came to rest on its left side between two trees that were 5 feet apart, and about 35 feet south of the initial impact point. The left skid was broken around a tree and the right skid was bent, and resting against the tree. The tailboom was severed at the fuselage and approximately 18 inches forward of the tailrotor gearbox, but remained attached by the tailboom cables and wiring. The cabin area was crushed and the fuselage displayed several transfers of leaves and tree bark. One of the helicopter's rotor blades was lying on the ground near the initial impact point; the other was snagged on a fractured tree limb about 30 feet above the ground. Control continuity was established from the cockpit to the main rotorhead. Control continuity was established from the cockpit area to the breaks in the tailboom. Continuity was established outboard of the breaks to the tailrotor. The flight controls were found jammed due to impact damage. The collective was found in the full up position and the cyclic was found jammed in the slightly aft position. The anti-torque pedal position was found with some left pedal input. Continuity was established throughout the helicopter's engine drive system. All of the drive system breaks were similar to torisional overload failures. Exam of the cooling fan revealed no rotational scoring. Examination of the helicopter's cooling system revealed a substantial amount of coolant at impact. MEDICAL AND PATHOLOGICAL INFORMATION An autopsy was performed on the pilot on December 4, 1998, at the office of the Chief Medical Examiner, Fairfax, Virginia. The FAA Toxicology Accident Research Laboratory, Oklahoma City, Oklahoma performed toxicological testing for the pilot on January 13, 1999. TESTS AND RESEARCH Examination of the engine and its maintenance records was performed at the Manassas Regional Airport, Manassas, Virginia, on December 17 and 18, 1998. Investigators from the Safety Board, FAA, and Rotax performed the examination. A review of the helicopter's maintenance records revealed that the pilot/builder made numerous changes to the engine performance hardware. These changes included the modification of the engine's jets, needles, spark plugs, and replacement of the exhaust system. According to the Rotax representative, "...the modified tuning and non-conforming parts of the engine from stock configuration..." was not recommended; however, some modifications, such as the "PEP" exhaust system, were recommended and marketed by the helicopter kit manufacturer. Examination of the engine revealed two different types of spark plugs were utilized, one of each type in the two cylinders. The spark plugs were wired such that one magneto fired one type of spark plug. Rotation of the crankshaft revealed 4 point scuffing on the cylinder and the Power Take-Off (PTO) piston. According to diagrams contained in a Rotax information paper published by California Power systems, the scuffing was similar to that of a seized engine due to "cold seizure" failure. The Rotax representative examined the pistons and concurred that the signatures were consistent with those produced by a cold seizure. He further stated that the scuffed areas included debris from an earlier engine malfunction wherein the builder had replaced several engine parts but had not completely removed the remnants of the old piston material. A review of the cooling system revealed that some of the cooling system components and coolant path did not follow the engine manufacturer's instructions. However, the coolant system did follow the kit manufacturer's instructions. Examination of the engine's thermostat, fuel filter, EGT thermocouples, and power take off (PTO) piston by the Safety Board's materials laboratory revealed no mechanical deficiencies. Metallurgical examination of the PTO cylinder walls revealed deposits from the side (piston skirt) of the accident PTO piston and the previous PTO piston. ADDITIONAL INFORMATION The Model 582 Rotax Engine manual contained the following warnings: 1. This engine, by its design is subject to sudden stoppage. Engine stoppage can result in crash landings, forced landings or no power landings. Such crash landings can lead to serious bodily injury or death. 2. This is not a certified 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. 3. 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 airplane wreckage was released to the pilot's wife on January 13, 1999.
the improper repair of the engine following a previous engine seizure which resulted in the loss of engine power over unsuitable terrain.
Source: NTSB Aviation Accident Database
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