SEATTLE, WA, USA
N86198
ENSTROM F-28C
WHILE EN ROUTE AT ABOUT 800 FEET AGL, THE HELICOPTER EXPERIENCED A COMPLETE LOSS OF POWER. THE PILOT MADE AN AUTOROTATION TO A CONFINED GRASSY AREA, BUT JUST PRIOR TO TOUCHDOWN HAD TO MANEUVER TO AVOID A PERSON IN THE AREA OF DESIRED LANDING. THE AIRCRAFT TOUCHED DOWN, BOUNCED, AND THEN EXPERIENCED A SKID COLLAPSE WHEN IT TOUCHED DOWN A SECOND TIME. AN INSPECTION OF ENGINE COMPONENTS SHOWED THAT ONE MAGNETO CONDENSER WAS SHORTING-OUT BY ARCING OVER ITS INSULATOR BASE, AND THE SECOND CONDENSER WAS SHORTING-OUT WHERE THE LEAD WIRE WAS EXPOSED THROUGH ITS INSULATION.
HISTORY OF FLIGHT On August 18, 1993, at approximately 1000 Pacific daylight time (PDT), an Enstrom F-28C helicopter, N86198, experienced a landing skid collapse while attempting a forced landing in Seward Park, near Seattle, Washington. The FAA certificated commercial pilot, who was the sole occupant of the aircraft, was not injured, but the aircraft sustained substantial damage. The aircraft, which departed Boeing Field/King County International Airport about five minutes earlier, was operating in visual meteorological conditions at the time of the accident. No flight plan had been filed and there was no report of an ELT activation. The pilot stated that he was about 800 feet above ground level, en route to a public relations static display, when the engine began to run rough. He therefore made a 180 degree turn in order to return to the departure airport. Just after reversing course, the engine lost power, and the pilot entered an autorotation toward a confined grassy area in a nearby park. As he approached the grassy area, the pilot noticed an individual sunbathing near where he planned to touch down. During his attempt to maneuver the aircraft away from this individual, the aircraft lost rotor rpm, and the pilot elected to attempt a "running landing." As the aircraft touched down, it bounced back in the air and touched down a second time. During the second touchdown, the left landing skid collapsed, and the tail rotor struck the ground. WRECKAGE AND IMPACT INFORMATION The aircraft impacted the ground at about 15 feet MSL in a confined grassy area near the shore of Lake Washington. At the point of initial impact, there were clear ground scars from both skids and the tail rotor stinger. From this point to the primary wreckage it was a distance of 46 feet on a magnetic heading of 102 degrees. The primary wreckage contained the main rotor and all of the airframe except components from the area near the tail rotor. The nose of the aircraft was pointing 340 degrees, and the left side of the fuselage was sitting on the ground as the left skid had folded outward and up. The right skid was still intact, but the tail boom had partially separated at the attachment bulkhead. Two out of the three main rotor blades showed impact scars, wrinkling of the skin, and bending from root to tip. The aft section of the tail boom had crushing and bending damage near where the tail rotor components had separated, but the fuselage forward of the tail boom attach bulkhead showed very little impact damage or scars. The tail rotor blades and tail rotor gear box were both located 59 feet beyond the main wreckage on a heading of 130 degrees magnetic. The tail rotor stinger, along with a short section of the tail rotor drive shaft was found 72 feet beyond the main wreckage at 160 degrees. The main portion of the tail rotor drive shaft came to rest 140 feet from the primary wreckage on a 180 degree heading. ADDITIONAL INFORMATION After the accident, a teardown inspection was made of the aircraft's induction air system, fuel supply system, and ignition system. No evidence of malfunction or damage was found in either the induction or the fuel system, but the inspection of the ignition system revealed discrepancies with both magneto condensers. The left magneto condenser showed a very clear arcing track where shorting had occurred across the insulation base. The lead wire of the right condenser had been crushed, and bare wires were showing through the insulation. Both condensers were replaced and a static engine run was successfully completed. The aircraft was released to Mr. Keith Nielson, a representative of the owner, at Seattle, Washington, on September 9, 1993.
SHORTED MAGNETO CONDENSERS. FACTORS INCLUDE A HIDDEN OBSTRUCTION IN THE LANDING AREA, AND A REDUCTION IN ROTOR RPM FROM ATTEMPTING TO AVOID THE OBSTRUCTION.
Source: NTSB Aviation Accident Database
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