Lake Havasu, AZ, USA
N2627M
ROBINSON HELICOPTER COMPANY R22 MARINER
Both the pilot and copilot of the helicopter were employed by and operating for a company that photographed boats in motion. The typical procedure was to fly low and slow on a path parallel to, and in the same direction as, the target boat; pass the boat; make a climbing 180-degree course reversal turn around the bow of the boat; and then descend and proceed to the next boat. During their second flight of the day, while nearing the completion of the course reversal turn to the right after a photo pass, the pilot initiated the descent for the next photo pass. The pilot added power and collective pitch to arrest the descent; however, he was unable to do so before the helicopter impacted the water. Although the tail boom was not recovered, no evidence of any preimpact failures with the helicopter was observed in the recovered wreckage. The course reversal turn was made from north to south, and the wind at an airport 17 miles to the northwest was out of the north at 15 knots. The pilot reported that the wind was about 12 knots gusting to 17 knots and that "clear air turbulence" was present. Although the exact wind conditions at the accident site were not known, evidence indicated that the helicopter experienced an overall wind change from a 12- to 15-knot headwind to a similar magnitude tailwind during the course reversal turn. Given the low speed of the photo pass, it is likely that the pilot did not correctly compensate for the wind speed and direction change during the course reversal and that the helicopter entered a vortex ring state (settling with power) due to the combination of low forward speed and the tailwind. The pilot's perception of, or attention to, the airspeed could have been adversely affected by his extra-cockpit focus on locating and tracking target boats. The pilot's attempt to arrest the descent by adding power and collective pitch was not the proper technique for recovery from the vortex ring state, but no evidence suggests that the pilot even recognized the onset of that condition. However, even if he did recognize its onset, the helicopter's altitude was likely too low to safely exit the vortex ring state because proper recovery from that state requires increasing the airspeed and/or lowering the collective pitch, which respectively either requires or results in a temporarily increased descent. Further, it is likely that the pilot was operating in a region of the height-velocity chart such that an autorotation would not have been successful.
HISTORY OF FLIGHT On October 27, 2012, about 1410 mountain standard time, a Robinson R-22 Mariner helicopter, N2627M, was substantially damaged when it impacted the surface of Lake Havasu, Arizona, during a commercial photography flight. The certified flight instructor pilot-in-command and private pilot rated co-pilot/trainee received minor injuries. The business flight was conducted under the provisions of Title 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and no Federal Aviation Administration (FAA) flight plan was filed for the flight. According to the pilot, the helicopter was temporarily based at Boulder City Municipal Airport (BVU), Boulder City, Nevada. Both the pilot and co-pilot were employed by a company based in Florida which photographed boats in motion, and marketed those photographs to the boat operators via its website "Boatpix.com." The co-pilot's primary function was to act as the photographer, while also learning the company methods, and occasionally flying the helicopter. Typically, the company and helicopter crews did not pre-coordinate with the boat operators being photographed; instead the crews patrolled and photographed all operating boats in a given location as targets of opportunity. The usual procedure was to fly "low and slow" on a path parallel to, and in the same direction as, the target boat, pass the boat, make a 180-degree course reversal turn around the bow of the boat, and then proceed to the next boat. The pilot did not cite any particular operational speeds for the photo passes. On the day of the accident, the crew flew from Boulder City to Lake Havasu, and photographed boats on the lake. They then landed at Lake Havasu Airport (HII), refueled and ate lunch, and departed on another photographic flight. The pilot was in the left seat, and the copilot was in the right seat, and they took turns flying to their planned patrol site. Once they neared their planned patrol area, the pilot took over the flying, and the crew began their photography operations. Subsequent to a photo pass on one boat, in accordance with the pilot's reported normal procedures, the helicopter climbed to about 50 feet above the water for the course reversal to the right. Also in accordance with those normal procedures, near the completion of the turn, the pilot began the descent for a photo pass on the next boat. However, the pilot was unable to arrest the descent via the addition of power and collective pitch, and the helicopter impacted the water. According to a verbal report by a law enforcement officer who responded to the accident, one eyewitness reported that while the helicopter was making a right turn, with its floats about 3 feet above the water, the main rotor blade struck the water, and the helicopter subsequently crashed. However, no written follow-up of the report or the witness's contact information was provided to the investigation. According to both crew members, after water impact, the helicopter immediately inverted, but they were both able to safely extract themselves from the submerged cockpit via their respective door openings. The crew was rescued by a nearby boat, and the helicopter was recovered to shore by a commercial marine salvage operator. The crew did not report whether they had successfully completed other photo passes subsequent their lunch break, or whether the accident pass was the first one since their break. PERSONNEL INFORMATION The pilot held a flight instructor certificate for helicopters. He reported that he had a total flight experience of approximately 1,009 hours, including about 938 hours in helicopters, of which about 850 were in the R-22. His most recent flight review was completed in January 2012 in the R-22, and his most recent FAA second-class medical certificate was issued in May 2012. The co-pilot held a private pilot certificate and was qualified in the R-22 helicopter. He reported a total flight experience of approximately 227 hours, all of which were in helicopters, and which included about 219 hours in the R-22. His most recent flight review was completed in July 2011 in the R-22, and his most recent FAA first-class medical certificate was issued in December 2011. In the initial NTSB interviews with the flight crew members, both individuals identified the co-pilot as a "passenger," but subsequent written information identified that individual as the co-pilot and trainee. AIRCRAFT INFORMATION FAA information indicated that the helicopter was manufactured in 1988, and was equipped with a Lycoming O-320 series engine. The helicopter was equipped with flotation devices ("floats") as its landing gear, to enable water landings as necessary. The photo operations were conducted with both cockpit/cabin doors removed. According to information provided by the pilot, as of the time of the accident, the helicopter had accumulated a total time (TT) in service of 5,750 hours. The engine had accumulated the same TT, and had a TT of 46 hours since its most recent inspection, and 1,762 hours since its most recent overhaul. The pilot reported that for the flight, the helicopter was about 71 pounds below its maximum certificated gross weight of 1,370 pounds. METEOROLOGICAL INFORMATION The 1356 automated weather observation at Needles Airport (EED), Needles, California, located about 17 miles northwest of the accident site, included winds from 030 degrees at 15 knots, visibility 10 miles, clear skies, temperature 28 degrees C, dew point minus 8 degrees C, and an altimeter setting of 29.93 inches of mercury. In his written report to the NTSB, the pilot stated that the wind direction was variable, with a speed of 12 knots and "5 knot gusts," for a top wind speed of 17 knots. The pilot also reported the presence of clear air turbulence and "light chop." The reported EED conditions yielded an approximate density altitude of 2,700 feet. WRECKAGE AND IMPACT INFORMATION The majority of the helicopter was recovered by a commercial marine recovery operator based at Lake Havasu. One float was separated from the helicopter during the accident sequence. The tail boom was not recovered. The fracture-separation of the tail boom had occurred at the juncture of the tail-boom and fuselage, and was consistent with water impact. The cockpit transparencies were fracture-separated from the helicopter, but except for that and some minor damage to the transparency frames, the cockpit was otherwise intact. Both main rotor blades exhibited damage signatures consistent with powered rotation at impact. Representatives from the FAA and the NTSB did not travel to the accident site, or examine the recovered wreckage in person. Neither the pilot nor the co-pilot initially reported any mechanical malfunctions, and examination of the wreckage photographs by the NTSB did not reveal any damage signatures consistent with pre-impact mechanical failure. ADDITIONAL INFORMATION Vortex Ring State According to the FAA Helicopter Flying Handbook (HFH, FAA-H-8083-21A), "vortex ring state" (or "settling with power") describes an aerodynamic condition where a helicopter may be in a vertical (with regard to the air mass) descent with up to maximum engine power applied, and little or no cyclic authority. The term "settling with power" comes from the fact that helicopter keeps settling, even though full engine power is applied. However, when the helicopter begins to descend vertically, it settles into its own downwash, which greatly enlarges the main rotor blade tip vortices. In this vortex ring state, most of the power developed by the engine is wasted in accelerating the air in a doughnut pattern around the rotor. A vortex ring state may be entered during any maneuver that places the main rotor in a condition of high upflow and low forward airspeed, including near-vertical descents of at least 300 feet per minute, and a horizontal velocity slower than that for effective translational lift. Vortex ring state susceptibility increases with increases in gross weight and density altitude. The HFH also noted that "when recovering from a settling with power condition, the tendency on the part of the pilot is to first try to stop the descent by increasing collective pitch. However, this only results in increasing the stalled area of the rotor, thus increasing the rate of descent. Recovery is accomplished by increasing forward speed, and/or partially lowering collective pitch." With sufficient altitude, temporary entrance into an autorotation will also enable safe exit from the vortex ring state. Robinson Helicopter Safety Notice SN-34 Robinson Helicopter Safety Notice SN-34, "AERIAL SURVEY AND PHOTO FLIGHTS -VERY HIGH RISK," was issued in March 1999, and revised in April 2009. The introductory paragraph of the SN stated that "There is a misconception that aerial survey and photo flights can be flown safely by low time pilots. Not true. There have been numerous fatal accidents during aerial survey and photo flights, including several involving Robinson helicopters." The SN further stated that "While maneuvering, the pilot may lose track of airspeed and wind conditions. The helicopter can rapidly lose translational lift and begin to settle. An inexperienced pilot may raise the collective to stop the descent. This can reduce RPM, thereby reducing power available, and causing an even greater descent rate and further loss of RPM." The SN closed by stating that "photo flights should only be conducted by well trained, experienced pilots" who have "extensive training in both low RPM and settling-with-power recovery techniques," and that pilots should "only fly the aircraft at speeds, altitudes, and wind angles that are safe and allow good escape routes." Height-Velocity Chart The helicopter manufacturer published a "height-velocity" (HV) chart in the Performance section of the Pilot's Operating Handbook. The chart presents the flight envelope (in terms of helicopter height above ground level and airspeed) for the safe conduct of an autorotation. Two shaded sections of the chart depict the regions from which a successful autorotation is unlikely. The HV envelope and chart are not operating limitations, but are intended as a guide for pilots to help them maintain awareness of the performance and operational capability of the helicopter. Operations in the shaded regions of the chart increases the risk exposure of the flight. There was insufficient information to determine which region of the HV chart the helicopter was operating in just prior to the accident.
The pilot’s unintentional and unrecognized entry into a vortex ring state as a result of conducting a course reversal turn into a tailwind while at a low altitude and airspeed, which resulted in an uncontrolled descent into water.
Source: NTSB Aviation Accident Database
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