19990102004149A

(.19) On January 2, 1999, at 2115 hours pacific standard time, a Bell 205A-1, landed hard during a forced landing in rustic canyon, about 7 miles southwest of the Van Nuys, California, airport. The forced landing was precipitated by a loss of engine power during a climb following takeoff. The aircraft sustained substantial damage. The commercial pilot and one crewmember were not injured. The other crewmember sustained serious injuries. The public-use helicopter was being operated by the los angeles city fire department as a training flight at the time of the accident. The flight originated at the Van Nuys airport about 2000 and a company visual flight rules (VFR) flight plan was on file. Night visual meteorological conditions prevailed. The pilot reported that the purpose of the flight was to practice "night-sun" operations. After 1 hour of training the pilot landed the helicopter on a dirt road so the crewmembers could switch seats. He reported that after conducting a crew briefing, he lifted off and began a climb to the north. The pilot stated that approximately 10 to 15 seconds later, and about 75 feet AGL, he initiated a left turn to the west. He reported that almost immediately after beginning the turn he heard a loud "clunking" sound, which was accompanied by vibrations. The engine then emitted a loud grinding, metallic grating sound. Simultaneously, warning lights, engine chip lights, and the RPM decay light became illuminated. The pilot reported that he immediately lowered the collective and entered autorotation. He stated that he did not have sufficient airspeed and altitude to reach the dirt road, so he started a 180-degree left turn down the canyon. The pilot performed a flare and near-vertical descent with little forward speed and the helicopter landed hard. The pilot reported that after egress of the aircraft, he did not smell or see smoke, nor did he note any fuel leakage. He further stated that the engine and rotors were stopped. The pilot reported that he had not experienced any mechanical problems with the aircraft prior to the onset of the engine problem. (.4)during a night training flight over mountainous terrain the pilot heard a loud 'clunking' sound, which was accompanied by vibrations. The engine then emitted a loud grinding, metallic grating sound. Simultaneously, warning lights, engine chip lights, and the RPM decay light became illuminated. The pilot lowered the collective and entered an autorotation but did not have sufficient airspeed and altitude to reach a dirt road, so he turned down a canyon and performed a hard flare and near-vertical descent with little forward speed. The helicopter landed hard and came to rest on rough uneven terrain surrounded by trees and high vegetation. Postaccident examination revealed that the engine power turbine as viewed from the exhaust exhibited damage. The number 4 turbine wheel was missing all of its blades and the blades on the number 3 turbine wheel were damaged. Scoring was evidenced on the inside diameter of the turbine case in the area of the nos. 3 and 4 turbine wheels. All the vanes and inner and outer supports of the second stage power turbine nozzle were displaced and/or missing, and fragments of the outer vane support were torn and distorted. The third stage turbine n ozzle exhibited extension damage on the trailing edges of the vanes and on the shroud/outer housing. Metallurgical exmination of the turbine components disclosed features indicative of overload fractures without evidence of material defects or fatigue. The metallurgist concluded that the overall type and degree of engine damage was indicative of a component failure in the second stage power turbine nozzle area; however, the cause of the component failure was not determined.