LAX00GA297

failure of the compressor turbine disc due to cyclic fatigue brought about by repeated operation near or above the engines' temperature/power limits by company personnel over an extended period of time. Factors in the accident were: 1) the high density altitude, mountainous terrain, and the helicopter's resulting marginal single engine performance capability; 2) the design, fabrication, and installation of the emergency external load release system, which had the power supply wired to the nonessential bus that would automatically drop offline during an engine or generator failure; and 3) the pilot's resulting inability to electrically release the water load, bucket, or line while dealing with the engine failure.

While flying along a mountain ridgeline to make a water drop on a wild fire, the helicopter lost power in one engine and collided with terrain as the pilot turned downslope toward a landing area. Ground crews watching the helicopter make its drop run observed smoke emanating from the right engine, then the helicopter made a left descending turn and impacted the downsloping mountainous terrain. A trailing pilot saw the helicopter about 150 feet above the ridgeline, then it made a sudden left descending turn. He did not see the pilot jettison either the water or the bucket. A teardown inspection and metallurgical examination of the No. 1 and No. 2 power sections was conducted. The examination of the No. 1 power section CT disc revealed that the firtree serrations adjacent to the No.s 24 and 25 blade positions were fractured above the blade retaining rivet hole, and that the No.s 27-29 firtree serrations were fractured at the blade roots. During the metallurgical examination, the failure of the CT disc was attributed to cyclic stress rupture due to extended and repeated operation of the engine at, near, or above its temperature/power limits. Dimensional measurements of the blades showed growth and deformation to the disk in the areas of the fractures. There were no material, manufacture, or design deficiencies identified during the metallurgical examination of the CT disc. The examination of the No. 2 power section revealed that the intermediate drive shaft fractured in a counterclockwise direction due to sudden stoppage of the left engine while it was at a high power level. Due to the degree of destruction and lack of dispatch records, the investigation was not able to accurately determine the operating weight of the helicopter at the time of the accident; however, for the 9,500-foot density altitude, it is believed that the helicopter's weight with the water load was at a point that resulted in marginal single engine capability at best. The accident helicopter had been modified with the installation of a water bucket and long line system. The long line and water bucket circuit breakers, and the emergency electrical release, were connected to the nonessential bus. This system was installed on a Form 337 field approval. According to the helicopter manufacturer, the electrical system is designed so that if one generator and/or engine failed both of the nonessential buses would automatically drop offline. Thus the emergency electrical release of the water bucket and long line would have been rendered inoperable in the event of a generator and/or engine failure. An override switch on the electrical panel can restore power to the nonessential buses; however, based on the event timeline reported by the witnesses, it is unlikely that the pilot could have restored power to the nonessential busses in time to prevent a collision with the ground.

1.1 HISTORY OF FLIGHT On August 13, 2000, at 1645 Pacific daylight time, a Bell 412 twin-engine helicopter, N174EH, collided with mountainous terrain while conducting a long line water drop along a ridgeline during a wildfire suppression operation near Cold Springs, Nevada. The wildfire was named the Twin Peaks fire. The helicopter was certified under 14 CFR Part 133 for external load operations and was being operated by the Bureau of Land Management (BLM) as a public-use firefighting aircraft. The helicopter, owned by Era Aviation, was destroyed. The airline transport pilot, the sole occupant, sustained fatal injuries. Visual meteorological conditions prevailed, and a company visual flight rules (VFR) flight plan had been filed. The helicopter departed the Twin Peaks helibase, located at Cold Springs, at 1605. The primary wreckage was at 39.34.83 north latitude and 117.48.56 west longitude. The accident pilot flew several missions the day of the accident. On the accident flight the pilot flew to the dip site, 3 miles south of the accident location, and then flew to the accident area to make a water drop. According to another pilot working the same dip site and fire, the accident helicopter was to make a water drop along the ridgeline to support the ground fire crews. The trailing pilot was going to make his water drop behind the accident helicopter. He was about 1 mile behind the accident helicopter, and observed the accident helicopter flying along the ridgeline. The accident helicopter made a sudden 90-degree left descending turn and impacted the downsloping mountainous terrain. There were no radio communications with the accident pilot immediately prior to the turn. The trailing pilot estimated the accident helicopter's altitude to be about 150 feet above the ridgeline, and that the accident helicopter was flying into the wind, which was 10 to 15 knots along the ridgeline. The trailing pilot indicated that the helicopter was "very low until impact" about 2/3 of the way down the hill. He did not know if the accident pilot had gotten rid of the bucket. He indicated that he did not see the accident pilot jettison the water. The fire crew from the Texas Initial Attack (IA) #1 were witnesses to the accident. A compilation of the witness statements indicated that they were about 1 ¼ miles away from the accident site. The witnesses stated that they observed the helicopter make a sudden left descending turn and impact the ground. They did not see the bucket release from the helicopter. One witness stated that he saw the helicopter start a climb along the ridgeline and saw a "puff of gray smoke come from his engine exhaust." Another witness stated that he saw the helicopter start up the ridgeline when he saw "white [and] blue smoke" coming from the right side of the engine. The crew boss assigned to the Texas IA #1 indicated that he was standing with the crew boss trainee just south of the crew bus. He stated that the crew boss trainee had just finished communicating via radio with the accident pilot; however, it was unclear if the pilot responded. The crew boss stated that the helicopter's forward motion "halted," and he saw about three or four "puffs of white smoke" coming from the exhaust area. The helicopter began to "roll and yaw," dropping to the side of the slope that he was traveling beside. Fueling records were not obtained at the accident site. However, in the operator's written statement (Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1/2), they estimated that the pilot departed the helibase with 1,000 pounds of Jet A fuel on board. 1.1.1 Helicopter Activities Prior to the Accident A couple of days before the accident, two ground crewmen from the Nevada Army National Guard watched for about an hour as the accident pilot filled up the Bambi bucket at a pond used as a helicopter dip site. On the east side of the pond there was a 5-foot berm. On the northwest corner was a small dry creek bed. According to the witnesses, the pilot would try and maneuver through the dry creek bed so that he didn't have to climb over the berm. One witness indicated that on some of his flares to fill the bucket, the pilot had "flared so hard the rotor wash would catch the Bambi and flip it up towards the rotor blades and come right out in front." The witness indicated that there was an abrupt manner when the pilot was filling the bucket. He observed the nose pitch down "quite a bit" to where it was about 6 feet off the water and then the pilot would try and get the bucket out of the water. There were a couple of times that the pilot would get the bucket "flying about 6 or 8 inches off the water," and if "he was not pulling enough power" the bucket would "go slamming back into the water." He stated, "It was a pretty abrupt move again to try and stop the aircraft and the bucket from going into the berm." A couple of times he had to put the bucket back into the water because the helicopter couldn't make it over the berm. The witness indicated that a couple of times, from his vantage point, it appeared that the bucket slid across the top of the berm. He further stated that at times during the pilot's maneuvers, he could see the tail boom "actually kind of almost wrinkle up," with some coning of the main rotor blades. At one point the pilot had to abort the dip because it appeared that he wasn't going to clear the berm. When the bucket went in "it pulled the back of the aircraft up. The back of the aircraft settled in and the second witness made a comment about how he [the pilot] had almost struck the tail rotor in the water." At that point both ground crew moved farther up the hill for safety concerns. The second witness indicated that the accident helicopter seemed to be in more of a hurry to fill the bucket than the other aircraft in the area. He also noted that the pilot's approach to "dipping" was very different from the other helicopter pilots. The pilot made a high speed pass, "kind of a high angle of bank turn then basically let the collective out of the [helicopter] and autorotate into the dip site and as the bucket hit the water he started to dragging it to fill it and then just pulled in all the power that he had." The accident pilot flew the bucket down the drainage area due to "bleeding rotor as he was going through translational lift." The second witness also observed, on a couple of passes, where the bucket swung out in front of the helicopter. The witness further indicated that the accident pilot appeared impatient, and that at one point tried to "sneak in front of the other helicopters." 1.5 PERSONNEL INFORMATION The National Transportation Safety Board investigator-in-charge (IIC) reviewed the pilot's Federal Aviation Administration (FAA) certified Airman and Medical information, as well as flight training records from Era Aviation, and Era's daily flight duty logs for the Twin Peaks fire. 1.5.1 Federal Aviation Administration Records Review of the pilot's medical information revealed that the most recent first-class medical certificate was issued on March 29, 2000. The medical contained limitations for vision, which indicated that the holder shall wear lenses that correct for distance vision and possess glasses that correct for near vision. On his medical application he reported having accumulated 14,200 hours of total pilot flight time, with 100 hours in the last 6 months. Review of the pilot's airman certification records disclosed that the pilot held an airline transport pilot certificate, as well as a commercial pilot certificate, both with ratings for rotorcraft-helicopter, along with an instrument rating for the BV-234. The pilot was type rated for the BH-212, BH-206 (VFR only), and BV-234. 1.5.2 Operator Records 1.5.2.1 Operator's Pilot Training Records The accident pilot's training records from Era Aviation indicated that he took a 1