CEN20LA136

The pilot’s failure to recognize and avoid the power line during the low-altitude flight. Contributing to the accident was the pilot’s fatigue, which affected the pilot’s ability to see and avoid the power line.

The pilot and passenger were conducting a low-altitude raptor survey flight. Witnesses reported seeing the helicopter flying just prior to its impact with powerlines about 85 ft above the ground. The witnesses described the helicopter in a gentle turn toward the sun prior to impact. One witness noted that he did not hear any unusual noises from the helicopter prior to impact. Automatic dependent surveillance-broadcast data from the helicopter provided information indicating the pilot flew six flights in the 24 hours prior to the accident. The accident flight was the fifth that day and occurred approximately 10 hours after the pilot had begun flying that morning. Intervals between flights that day were 17, 24, 35, and 29 minutes. These working conditions were conducive to fatigue. Research on pilot fatigue in a noisy, vibrating helicopter simulator found considerable increases in subjective fatigue after 6 hours of short repetitive flights. At the end of this period, some helicopter pilots who participated in the study said they were so fatigued that they did not feel safe to fly a real helicopter. As subjective fatigue increased, study pilots demonstrated increasingly frequent “lapses” in performance. While missions the day of the accident were longer than those in the study, flights were conducted at low altitude and involved repetitive observation tasks that required a high state of awareness to avoid terrain and obstacles. This heightened state of awareness would produce a mental workload similar to the shorter repetitive IFR flights in the study; therefore, it is likely that similar effects would be expected, including lapses in performance as fatigue increased. These lapses in performance were described in the study as outliers caused by moments of inattention. The accident pilot’s ability to avoid the same wire nine times earlier that day, but not avoid it during the accident flight is consistent with an attentional “lapse.” This potential lapse combined with over 10 hours since awakening, and 8 hours flight time already accumulated the day of the accident suggests that the pilot was likely fatigued during the accident flight and that fatigue likely challenged the pilot’s ability to see and avoid the power line.

The helicopter came to rest in a field next to the west side of Robin Avenue and south of 240th Street. The wires that were struck ran along the north edge of 240th Street, strung between poles that were about 100 ft. tall. The estimated height of the wires struck was about 85 ft. above the ground. Figure 3. Location of powerlines, helicopter flight path, and wreckage. A post-impact fire consumed most of the cabin section of the helicopter. A postaccident examination of the helicopter after it was removed from the site revealed no preimpact anomalies. A large wire was found wrapped around the rotor mast just below the main rotors. Figure 4: Powerline wires wrapped around main rotor mast. On March 31, 2020, about 1626 central daylight time, a Robinson R44 helicopter, N107EH, was destroyed when it was involved in an accident near Audubon, Iowa. The pilot and passenger were fatally injured. The helicopter was operated as a Title 14 Code of Federal Regulations Part 91 aerial observation flight.   According to the operator, the purpose of the flight was to conduct a raptor survey of a 442 square-mile area in western Iowa under contract with another company whose biologist was the passenger on the helicopter at the time of the accident. The helicopter was flying a north-south grid pattern when two witnesses observed the helicopter flying in a southerly direction at low altitude. One witness observed the helicopter strike the bottom two wires of a power line before it impacted terrain and burst into flames. The second witness lost sight of the helicopter just before it impacted the wires but heard the impact and observed the helicopter descend with wires intertwined in the main rotor. Both witnesses thought the helicopter was in a turn to the southwest, toward the sun, prior to the hitting the wires. One witness described the helicopter in a gentle turn, not in a way that looked like the pilot was aware of the high lines. Automatic dependent surveillance- broadcast (ADS-B) data showed that during the final moments of the accident flight, the helicopter was travelling south over Robin Avenue, approaching 240th Street, at an ADS-B-reported geometric altitude of 1,475 ft, with a ground speed of about 85 kts. The final recorded data point was about 160 ft north of the wires that were struck. There were no deviations in heading or altitude before the end of the data. The ground elevation at the accident site was about 1,460 ft. The flights within the survey area were conducted at altitudes about 100 ft above the ground. Examination of the flight track data for the previous flight showed that the helicopter had crossed the power lines on at least two occasions during the previous flight. (See Figure 1.) Based on ADS-B flight data and the pilot’s flight records, he had flown a flight the night prior to the accident that concluded in the Sioux Falls, South Dakota, area, lasted about 45 minutes, and was followed by about 9 hours of non-flight activity. It is not known what the pilot did during this time of non-flight activity. On the day of the accident the pilot flew five flights lasting 51 minutes, 18 minutes, 3 hours 29 minutes, 3 hours 11 minutes, and 22 minutes, respectively. The first flight of the day took off at 0629. Between these flights were periods of non-flight activity lasting 17 minutes, 24 minutes, 35 minutes and 29 minutes, respectively. It was reported that the biologist joined the flight after the helicopter arrived at Arthur N. Neu Airport (CIN), Carroll, Iowa, after the second flight of the day. Figure 1: Plot of the survey area and the helicopter flight path on the day of the accident. Figure 2: 3-dimensional view of the final portion of the accident flight path.