SEA07FA006

The complete loss of engine power, for undetermined reasons, while on final approach, and the pilot's loss of control of the helicopter after the power loss. Factors include a lake below the final approach to the private landing pad.

While the pilot was on final approach to a landing pad near his private residence, the helicopter experienced a total loss of engine power while approximately 100 feet above the surface of a lake. The pilot did not apply the proper flight control inputs to maintain a controlled autorotation to the surface of the lake, and therefore the aircraft spun multiple times around its vertical axis while descending to an uncontrolled impact with the water. Immediately after impacting the surface of the lake, the helicopter sank in about 20 feet of water. There was no indication of any mechanical failure or malfunction.

THIS CASE HAS BEEN MODIFIED OCTOBER 30, 2007. HISTORY OF FLIGHT On October 8, 2006, approximately 1600 Pacific daylight time, a Robinson R44 helicopter, N769RT, impacted the surface of Lake Tapps, near Sumner, Washington, and sunk in about 20 feet of water. The private pilot received fatal injuries, his passenger received serious injuries, and the aircraft, which was owned and operated by the pilot, sustained substantial damage. The local 14 CFR Part 91 personal pleasure flight, which departed the same area about 50 minutes prior to the accident, was being operated in visual meteorological conditions. No flight plan had been filed, and there was no report of an ELT activation. According to the passenger, the flight was "kind of a spur of the moment event." She stated that the fact that the flight had not been a pre-scheduled event was not unusual, and that it "happened often." She said that she and the pilot had been talking, and jointly decided to go take a look at some property that the pilot was "developing" in the general area. After departure from an area near the pilot's home, the flight proceeded south about 10 miles to the Orting/Carbon River area, where the pilot took about five minutes to look around. After that, he headed northeast for about seven miles to the town of Buckley, where he over-flew some property he wanted to observe. He then headed west, paralleling Highway 410, until he got to the Meyers Road area. At that point, the pilot over-flew the house of a friend. He then told the passenger that he was going to land in an area near the house, but after the passenger told him that she was uncomfortable with the landing zone, he elected not to land. He then decided to proceed back to the original point of departure. According to the passenger, when they came back to the general area from which they departed, the pilot maintained approximately the same altitude he had been at en route, until he reached an area about one-half mile north of the landing site. At that time he turned south, toward his home (and landing site), and started a descent that brought them in low over the trees that are on a ridge just to the south of 16th Street East (see map). According to the passenger, as they continued the descent toward the landing site, the pilot suddenly made a rapid movement of the stick (cyclic) toward the left. This was followed almost immediately by the helicopter "jerking violently" to the right (clockwise rotation). The helicopter then seemed to her to stabilize for one to two seconds, during which time she asked the pilot what was wrong, and he responded with, "I don't know." The helicopter then started spinning to the right and descending. The passenger believes that the helicopter spun around two full times, and then impacted the water "very hard." At the moment of impact, she felt something "snap or break" in her back, and then the aircraft almost immediately filled with water and sank rapidly to the bottom. After it came to rest on the bottom of the lake, the passenger looked and felt for the pilot, but could not determine where he was, so she unlatched her seatbelt, pushed up through an opening, and swam to the surface. In a post-accident interview, the passenger said that just about the time the helicopter started to spin, she saw a number of "warning lights" come on, but she did not remember hearing any aural warnings. She further stated that she was not aware of any changes in engine rpm, nor did she remember hearing anything unusual from the engine. She did report during the interview that she was later told by her daughter and another person who were standing near the landing site watching them approach, that the engine had made a couple of loud "pops" just before the helicopter began spinning. A number of witnesses on the ground observed the aircraft as it arrived in the area and proceeded toward the landing site. In addition to the passengers daughter, six of those witnesses stated that they heard the engine "backfire" or "pop" between one to three times just prior to, or during the aircraft's spiraling descent. Most of the witnesses that heard the noises said that there was a sudden decrease in the engine rpm just after the sequence of rapid popping or backfiring. One witness reported that the engine rpm had suddenly increased just prior to the popping, and then rapidly decreased immediately after the reported noises. One witness said that the noise was either a pop or a loud "clunk." This same witness said that the engine momentarily "revved higher" just after the pop, and then the rpm decreased, and that the engine did not come to a stop. None of the witnesses reported seeing anything separate from the aircraft during the sequence of events. One witness said that he clearly saw the main rotor blades slow dramatically or stop at the beginning of the descent, and that he heard the engine "stop running." One witness said that to him the sound was more like a "mechanical pop" than an engine backfire. A number of the witnesses that went out in the water to try to help the occupants reported a strong gasoline smell around the impact area. A number of witnesses estimated that the helicopter was about 100 feet above the water when the accident sequence began. WRECKAGE AND IMPACT INFORMATION The helicopter came to rest on the muddy bottom of the lake in about 20 feet of water. It was recovered from the lake the day after the accident, and taken to AvTech Services, LLC, in Maple Valley, Washington, where it underwent a post-accident inspection. That inspection revealed that the airframe was basically intact, but severely distorted due to hydraulic impact damage. There were numerous failures of flight control torque tubes, all of which were consistent with impact sequence overload. The tail cone was still attached to the aircraft body, and the empennage was still attached to the aft tail cone bay. The lower surface of both the aircraft body and the most-forward six bays of the tail cone showed severe hydraulic crushing. The empennage was intact, but the stabilizer was bent slightly downward. All four of the rubber drive belts were intact in their respective pulley grooves, and none showed any signs of rolling or slipping. The belt tension actuator was fractured, but otherwise appeared normal. The sprag clutch looked and functioned normally, and the main rotor gearbox was undamaged and rotated freely. The tail rotor driveshaft had been bent during the impact sequence, but it showed no indication of pre-impact rotational damage. Both the intermediate and aft flex couplings were intact, and the tail rotor gearbox was intact and free to rotate. The tail rotor gearbox was drained, and contained mostly water, with numerous small droplets of blue lubricating oil. The tail rotor output shaft, hub, blades, pitch change links, and pitch change slider were all undamaged and were free to function normally. After the airframe and engine inspection at AvTech Services were completed, the engine was sent to Textron Lycoming production facility in Williamsport, Pennsylvania, where it underwent a Federal Aviation Administration monitored test run on the production automated engine test stand. The engine test run sequence lasted for a total of 31 minutes. During the test sequence, the engine was run at 1,500 rpm for five minutes, 1,800 rpm for five minutes, 2,200 rpm for five minutes, an additional 2,200 rpm for one minute (for magneto check), full throttle (2,783 rpm and 25.5 inches of manifold pressure) for ten minutes, and 600 rpm (idle) for five minutes. At each test rpm, data was recorded for allowable speed variation, and cylinder head temperature. At full power and at idle additional measurements were made for oil pressure, and oil gallery temperature. At full power, fuel pressure was also recorded. Except for one parameter, oil pressure at full power, all recorded data points were within acceptable limits,