WPR13GA128

The pilot’s failure to maintain clearance from a wire while maneuvering during low-altitude operations. Contributing to the accident was task- and/or work-related fatigue.

The pilot was flying a helicopter as part of a Department of Interior (DOI) reseeding project when the helicopter struck the static line above a set of power transmission lines. Postaccident examination of the engine and airframe revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation. The length and direction of the debris field was consistent with the helicopter traveling in the direction of, and at a rate of speed consistent with, a seed dispersal run. The pilot was familiar with the area and was aware of the transmission lines, having performed a reconnaissance flight and flown over them multiple times during the previous flights that day. In the area of the accident site, the power lines began an ascent up an adjacent hill, with the static lines diverging such that they were about 40 feet higher than the power lines at the collision location. The static lines were of thinner gauge and could easily have been obscured by the surrounding hilly terrain. The lines were depicted on the relevant Federal Aviation Administration sectional chart. The helicopter was not equipped with a wire strike protection system nor was it required to be under the terms of the DOI contract. Neither the power nor static lines were equipped with visibility markers nor were they required to be due to their elevation above ground level. The pilot had flown 40.5 hours over the last 5 days as part of the reseeding project, which was just short of the DOI contract maximum. A review his sleep history indicated that he received adequate rest the night before the accident. On the morning of the accident, he had flown 10 application runs in an area about 70 miles away. He took a lunch break about 3 hours before the accident, then flew 20 separate seed application runs and 10 reloads. His total flight time for that day was 6.6 hours. The low-level and "nap of the earth" flight operations required considerable concentration, most likely resulting in task-and/or work-related fatigue at the end of the day. By comparison, the United States Army recommends a maximum flight time of 8 hours per day or 37 hours per week, with a reduction of a factor of 1.3 to 1.6 for low-level and "nap of the earth" flying; thus the pilot would have exceeded their duty hour recommendations for each of the 5 days leading up to and including the accident day. The pilot held an assisted special issuance second-class medical certificate based on a reported history of diabetes for which he was taking medication. His most recent medical examination revealed a new diagnosis for hypertension, as well as preexisting cataracts in both eyes, which exhibited no change since his last examination a year prior. In part due to the lack of an autopsy, the relevance of these findings, combined with his likely work-related fatigue, could not be determined.

Navigation Systems The helicopter was equipped with an Automated Flight Following System (AFF), an Ag-Nav GPS based agricultural navigation system, and a Garmin GPSMap 496 GPS receiver. The AFF system transmitted positional reports without altitude information to the U.S. Department of Agriculture Forest Service data center at roughly 2-minute intervals; the last recorded position occurred at the accident site at 14:23:38. The Garmin unit did not contain any data for the accident flight, and was most likely off at the time of the accident. The Ag-Nav system was utilized by the pilot to disperse seed, and was configured to record its position every 0.6 seconds. In addition, the unit was capable of recording heading, altitude, and "spray" status. The unit sustained impact damage, and was sent to the National Transportation Safety Board Office of Research and Engineering for examination, and then to Ag-Nav in Ontario, Canada, for data extraction. The data corroborated the AFF information, albeit at a higher resolution. The data revealed that the helicopter had administered seeds in the area over the course of 20 separate passes prior to the accident. Each pass was oriented north-south, about 1 mile long and 80 feet apart, with the helicopter typically returning to be reloaded after every 2 passes. The power transmission lines and two of their associated towers transected the area, with the helicopter flying over the lines on every pass. Throughout the passes, the helicopter maintained a ground clearance of between 100 and 200 feet agl. The last recorded position was located about 2,000 feet south of the main rotor blades and power lines, at the southern boundary of the application area. At that time the helicopter was climbing from 6,634 to 6,696 feet, and transitioning from the pass heading of 162 degrees true, to 172 degrees. The unit recorded that the spray system was set to off just prior to the helicopter reaching the southern boundary. The final position reports and spray status followed a similar profile to the other passes, and were consistent with the pilot initiating a climbing right turn for an application run. The impact sequence was not recorded. According to representatives from Ag-Nav, the unit contains a 10-second memory buffer, and as such will not record the last 10 seconds of data if electrical power is unexpectedly interrupted. Helicopter Exam The engine sustained minimal damage during the accident sequence, and remained attached to its airframe mounts. All engine controls remained attached, and all fuel, pneumatic, and hydraulic lines remained firmly in place at their fittings. The stage 4 turbine wheel appeared intact, and there were no indications of oil leaks or catastrophic engine failure. The rotor mast remained attached to the airframe, and was canted about 45 degrees aft along with the main rotor gearbox. The collective and cyclic control linkages had sustained varying degrees of impact damage from the main rotor gearbox through to the head; both were bent at and separated from their respective fittings. Examination of the main rotor head revealed that it had separated from the mast just below the droop stops. The mast exhibited bending damage to both sides in the immediate vicinity of the break. Tail rotor drive train continuity was established from the main gearbox through to both tail rotor blades, with the drive shaft separating from the main gearbox at the output coupling. The tail rotor pitch control tube had been cut at the bulkhead by recovery personnel, and remained continuous through to the tail rotor pitch links. Pilot Itinerary The pilot began the seeding mission on the morning of February 13, when he departed from his home airport in Elko, Nevada, in the accident helicopter. For the next 4 days, he accumulated about 8 hours of flight per day, totaling 33.9 hours. On the day of the accident he accumulated 6.6 hours of flight time, and as such his 5-day total for the period leading up to the accident was 40.5 hours. Examination of the pilot's flight history for the prior 2 months revealed 6-day flight time totals of between 8 and 28.4 flight hours. The helicopter fuel truck driver had been working with the pilot all week for the seeding operations. They had shared a hotel room each evening in order to reduce expenses. On the night prior to the accident, the pilot went to bed at 2030 and awoke at 0530. He was not aware of the pilot waking up or having sleeping problems during the night. He stated that he had shared rooms with the pilot on prior missions and that nothing about that evening stood out as unusual. Pilot Fatigue Issues With regards to the effect of time-on-task as a cause of fatigue and an influence on performance among helicopter pilots, one such study (A.M. Stave, "The Effects of Cockpit Environment on Long-Term Pilot Performance," Human Factors, Vol. 19 (1977)), examined the effect of a helicopter cockpit environment and continuous flying activity on subjective fatigue and pilot performance. For this study, flight legs were designed to simulate repetitive circular, helicopter air taxi flights conducted under instrument flight rules in a metropolitan area, with complete circuits lasting about 1 hour and including three approaches and landings. Pilots flew for flight periods varying between 3 and 8 hours, with rest breaks permitted during the 4- and 8-hour flight periods. Pilot performance was measured, and the pilots also provided ratings of subjective fatigue each hour. Time-on-task and subjective fatigue were found to have no effect on some basic aspects of flying performance, but they were associated with increased "lapses" in performance, such as navigational errors. The study found that subjective fatigue increased with time-on-task, peaking during the last hour of flight, but scheduled breaks delayed the onset of subjective fatigue. Flight Time and Duty Period Limitations The DOI contract specified limits for the pilot, which capped flight time during any assigned duty period to 8 hours. Thirty-six or more flight hours in a consecutive 6-day period required the next calendar day off duty, with a maximum of 42 hours in any consecutive 6-day period. These flight limitations exceeded those required under the rules pertaining to agricultural aircraft operations, governed under Federal Air Regulations part 137, which do not set specific flight time limitations. By comparison, United States Army flight regulations (Headquarters Department of the Army, Aviation Flight Regulations, U.S. Army Regulation 95-1(Washington, DC: HQDA, 1997)) allow local commanders flexibility in developing flight time limitations for helicopter pilots, but they recommend that flight time be limited to 8 hours per 24-hour period, 15 hours per 48-hour period, and 37 hours per week. Army regulations also recommend that maximum helicopter pilot flight times be reduced by factors of 1.3 for day contour or low-level flight and 1.6 for day, "nap of the earth" flight. These recommendations were developed based on data which indicated that low-altitude flight profiles following terrain contours and lower-altitude, terrain-hugging flights were more fatiguing for pilots than higher-altitude flights. Power Transmission Lines According to the power company, the base of the transmission tower to the east of the accident site was at an elevation of 6,557 feet, with the west tower at 6,870 feet. The power cables were attached to the towers about 45 feet above the ground, with the static lines a further 20 feet higher. The towers were separated by a distance of about 1,800 feet, and the power cables sagged about 40 feet below the static lines at the center point. Neither the power nor static lines were equipped with visibility markers; their height above the ground did not require the use of such markers. The accident site was located within the area covered by the FAA Las Vegas