Hawthorne, CA, USA
N670EM
AIRBORNE XT 912
The student pilot of the weight shift control (WSC) light sport aircraft, commonly referred to as a "trike," advised the air traffic control (ATC) tower that she was ready for departure and was instructed to hold short. A DeHavilland DHC-6 then landed, and, about 40 seconds later, the controller cleared the trike for departure on the same runway. When the trike was about 50 ft above ground level, it entered a steep right bank and descended to ground impact just north of the east-west runway. Postaccident examination of the airframe and engine did not reveal evidence of any pre-impact anomalies. Trajectory comparisons of the two aircraft, revealed that the trike likely encountered one of the wingtip vortices from the DHC-6, and the strength of that vortex, depending on the encounter geometry, likely far exceeded the roll authority of the trike. This resulted in an airborne loss of control at an altitude too low for recovery. Because the trike and the DHC-6 were of the same ATC weight category, no controller wake vortex advisory was required or issued, and all wake-separation decisions were the responsibility of the pilot. Despite the significant size and weight differences between the 10,500-pound DHC-6 and the 992-pound trike, the pilot opted to depart less than a minute after the DHC-6 landed. Review of the pilot's training syllabus indicated that wake vortices were part of the curriculum, but her actual knowledge and understanding of that subject could not be determined. Her training workbook appeared to be pristine and unused, and the instructor's signoffs appeared to all have been done in a single sitting, possibly even after the accident. This suggested the possibility that her training, academic knowledge, and study diligence left her inadequately prepared to appreciate and avoid the wake vortex hazard. Although the toxicology results indicated that the pilot had smoked cocaine, it was not possible to determine whether or not the pilot was experiencing any effects from smoking cocaine or from withdrawing from cocaine at the time of the accident. Based on the levels of diphenhydramine found, the pilot may have been impaired by its effects (somnolence, slowed psychomotor responses) at the time of the accident.
HISTORY OF FLIGHTOn March 21, 2016, about 1201 Pacific daylight time, an Airborne XT912 weight shift control (WSC) special light sport aircraft, N670EM, was destroyed when it impacted a fence and a roadway shortly after takeoff from Northrop/Hawthorne Municipal Airport (HHR), Hawthorne, California. The student pilot received fatal injuries. The aircraft was owned and operated by Pacific Blue Air (PBA) of Venice, California, and was based at HHR. The instructional flight was operated under the provisions of 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and no flight plan was filed for the flight. According to multiple witnesses, the aircraft initiated its takeoff roll from HHR's runway 25 at a point before the displaced threshold. Just after liftoff, the aircraft began to bank and turn right and continued to do so until its flight track was nearly perpendicular to the runway heading. The initial segment of the flight was a climb but became a descent as the aircraft rolled and turned right. Witness estimates of the aircraft's maximum altitude ranged between 40 and 200 ft, and their maximum bank angle estimates ranged between 45° and 90°. All witnesses reported that the engine rpm either remained constant or increased during the flight and that the engine continued to run at least until impact. None of the witnesses mentioned the presence of any other aircraft. The aircraft struck the airport perimeter fence and then impacted a 4-lane road north of the airport that ran roughly parallel to runway 25. According to witnesses, on impact, the aircraft immediately caught fire. A water pumping/construction crew was working about 100 ft from where the aircraft impacted, and several of these workers responded to the site within a few seconds and attempted to rescue the pilot and extinguish the fire. Two Los Angeles County Sheriff's Department deputies, who were located several hundred feet from the impact site, responded within a minute of the accident. Air traffic control tower (ATCT) personnel notified HHR operations personnel of the accident, and they responded within a few minutes of the accident. Los Angeles County Fire Department (LACoFD) equipment and personnel also responded very shortly after the accident. The pilot was extracted from the wreckage and transported to a hospital. The wreckage was examined and documented on scene by Federal Aviation Administration (FAA) and National Transportation Safety Board (NTSB) personnel later the same day and was then recovered and transported to a secure facility for additional examination. PERSONNEL INFORMATIONPilot's Flight Experience The pilot held an FAA student pilot certificate that was issued in May 2014. Review of her pilot's logbook indicated that her first flight was conducted in October 2013 and that she flew about 2 to 3 times per month thereafter. All flight time recorded in the logbook was in WSC aircraft, and the PBA Chief Pilot reported that the pilot had no flight time in any other type of aircraft. All of the pilot's flight time through June 2015 was in an Evolution Revo WSC aircraft that was also owned by PBA. The logbook indicated that the pilot had accrued about 38 hours in the Revo before she switched to the accident aircraft. The pilot's first flight in the accident aircraft was on June 8, 2015, and all her subsequent flights were in the accident aircraft. The logbook indicated that the pilot had accrued about 21 hours in the accident aircraft. The pilot's first solo flight was accomplished on November 2, 2015, when she had a total flight experience of about 48 hours. The logbook listed 8 solo flights, with a total flight time of 6.9 hours. Her most recent flight, which was a solo cross-country flight, took place on March 16, 2016. Except for two flights, all the pilot's dual flights were conducted with the PBA Chief Pilot. Pilot's Recent Activities According to the pilot's family, the pilot had experienced a significant snowboarding accident about 3 days before the accident flight. The family members reported that she struck her head or neck in that event. She was wearing a helmet, did not lose consciousness, but did suffer a "strained neck." The pilot's fiancé reported that she was sore from that event, but her behavior, personality, and mental acuity were unchanged. The pilot's fiancé reported that she was happy when she left their residence for the accident flight and that he did not speak to her after she left. A PBA co-owner reported that she witnessed the pilot arrive at the airport and stay in her car on the phone for about 20 minutes. According to the co-owner, when the pilot came into the hangar she appeared "slightly agitated." Review of the pilot's telephone records indicated that between 1040 and 1122 she made five calls to four different numbers and received one call from one of those numbers. The longest call was 3 minutes in duration; the rest were 1 minute in duration. In that same period, she was sent one text message from a fifth telephone number. The investigation did not determine the persons or agencies associated with those telephone numbers. AIRCRAFT INFORMATIONFAA information indicated that the aircraft, commonly referred to as a "trike," was classified and registered as a light sport aircraft (LSA). It was manufactured in 2007 and was equipped with a Rotax 912 series engine. The maximum takeoff weight was 992 lbs. The aircraft manufacturer (Airborne) was based in Australia, and the engine manufacturer (Rotax) was based in Austria. According to the PBA Chief Pilot, the aircraft was acquired by PBA about a year before the accident and was equipped with an "SST" model wing. According to the aircraft manufacturer's publications, the SST wing is "a high performance flex wing, which utilises struts to react the negative flight and landing loads imposed on the wing airframe. Removal of the king post and associated top rigging results in a significant decrease in drag, which improves cruise performance and reduces fuel consumption." The documentation also stated that, "Handling is improved and speed ranges are increased... pitch stability is achieved by using wire braced washout struts…which serve to keep the trailing edge of the sail raised, maintaining washout and therefore pitch stability." The documentation closed by stating that, "The SST retains all of the great handling characteristics of the Airborne wing range. The performance benefit of the strutted version ...makes the XT912 / SST aircraft the choice for the discerning cross country pilot." Review of the aircraft maintenance records revealed that the most recent annual condition inspection was completed on June 3, 2015, when the airframe and engine each had accumulated 232 hours since new. The most recent 100-hour inspection was completed on November 10, 2015. The records indicated that, at that time, the airframe and engine each had accumulated 400 hours since new. The maintenance records did not contain any entries documenting maintenance actions that were indicative of, or could be associated with, any previous significant damage or problems. METEOROLOGICAL INFORMATIONThe 1153 HHR automated weather observation included calm winds, visibility 10 miles, clear skies, temperature 19°C, dew point 11°C, and an altimeter setting of 30.12 inches of mercury. The next HHR observation was issued at 1253 and reported winds from 270° at 8 knots. About 8.5 minutes before the aircraft was cleared for takeoff, the ATCT local controller broadcast, "Attention all aircraft ATIS [automated terminal information service] lima is now current wind two six zero at four altimeter three zero one four." Between that broadcast and the accident, the local controller did not issue any other wind information to any of the aircraft that he was handling. AIRPORT INFORMATIONFAA information indicated that the aircraft, commonly referred to as a "trike," was classified and registered as a light sport aircraft (LSA). It was manufactured in 2007 and was equipped with a Rotax 912 series engine. The maximum takeoff weight was 992 lbs. The aircraft manufacturer (Airborne) was based in Australia, and the engine manufacturer (Rotax) was based in Austria. According to the PBA Chief Pilot, the aircraft was acquired by PBA about a year before the accident and was equipped with an "SST" model wing. According to the aircraft manufacturer's publications, the SST wing is "a high performance flex wing, which utilises struts to react the negative flight and landing loads imposed on the wing airframe. Removal of the king post and associated top rigging results in a significant decrease in drag, which improves cruise performance and reduces fuel consumption." The documentation also stated that, "Handling is improved and speed ranges are increased... pitch stability is achieved by using wire braced washout struts…which serve to keep the trailing edge of the sail raised, maintaining washout and therefore pitch stability." The documentation closed by stating that, "The SST retains all of the great handling characteristics of the Airborne wing range. The performance benefit of the strutted version ...makes the XT912 / SST aircraft the choice for the discerning cross country pilot." Review of the aircraft maintenance records revealed that the most recent annual condition inspection was completed on June 3, 2015, when the airframe and engine each had accumulated 232 hours since new. The most recent 100-hour inspection was completed on November 10, 2015. The records indicated that, at that time, the airframe and engine each had accumulated 400 hours since new. The maintenance records did not contain any entries documenting maintenance actions that were indicative of, or could be associated with, any previous significant damage or problems. WRECKAGE AND IMPACT INFORMATIONThe wreckage was located about 280 ft north of the HHR runway 7/25 centerline, and about 1,400 ft west of the east end of the paved runway surface. The airport boundary was a 6-ft-high steel chain link fence, and ground scars indicated that the aircraft struck and damaged the fence, and then first impacted the road about 15 ft north of the fence. The aircraft came to rest at the north edge of the road, adjacent to and in contact with a fenced electrical equipment enclosure. The fence damage, road scar, and wreckage formed a line that was perpendicular to the runway. Except for the right main wheel assembly and about a dozen windscreen, fairing, and propeller fragments, all the wreckage was tightly contained. The airframe (carriage) and wing structure consisted primarily of aluminum tubing of varying diameters, stabilized by a number of steel cables. Portions of several tubes had been damaged or consumed by fire. The carriage came to rest on its right side, oriented with the nose pointed about southeast. All the steel cables remained intact and securely attached to the structure at each of their respective ends. The forward carriage frame and nose landing gear assembly was fracture- and/or fire-separated from the aft carriage frame. The right wheel assembly was fracture-separated from the aircraft just above where its three support struts attached to the wheel assembly. The wheel exhibited significant localized crush damage, consistent with contact with the top crossbar of the airport boundary fence. The seats were not located/identified in the wreckage, consistent with consumption by fire. Four instruments (an airspeed indicator, a radio, a transponder, and an EFIS [electronic flight instrumentation system]) were identified in the wreckage, but all were severely fire-damaged. The airframe recovery parachute was found out of its container; it remained reefed/folded but was partially extended lengthwise, and much of it was fused or consumed by fire. The parachute extraction rocket was also found out of its container, and its propellant load was absent, consistent with having been consumed in the ground fire. Detailed examination of the airframe wreckage did not reveal evidence of any pre-impact mechanical deficiencies or failures that would have precluded normal flight. The engine remained attached to its steel frame portion of the carriage and did not exhibit any evidence of any preimpact failures. The engine sustained significant impact and fire damage, to the point where its pre-accident integrity and operability could not be ascertained. The three-blade Warp Drive composite propeller remained attached to the engine. Two propeller blades were fracture-separated from the hub; the full lengths of all three propeller blades were identified on scene. All propeller damage was consistent with impact effects with the engine operating. For additional details, refer to the NTSB public docket for this accident. ADDITIONAL INFORMATIONATC Separation & Advisory Information FAA guidance for air traffic controllers is published in the FAA Order JO 7110.65, "Air Traffic Control." According to the order, separation criteria are based upon the weight categories of the aircraft involved. The guidance listed four weight categories. In order of increasing weight, these were small, large, heavy, and super. Per the order, the small category is the lowest weight category and applies to aircraft weighing 41,000 pounds or less. The accident aircraft and the DHC-6, which weighed about 15 times what the accident aircraft weighed, were both in this category. For two aircraft in the small category, the only ATC-required separation criterion was that the preceding landing aircraft (in this case, the DHC-6) had to be clear of the runway before the succeeding aircraft (in this case, the accident aircraft) could be cleared for takeoff from the same runway. There was no requirement to issue a cautionary wake turbulence advisory between two small category aircraft. Paragraph 2-1-20 (b) of JO 7110.65 stated, "Issue cautionary information to any aircraft if in your opinion, wake turbulence may have an adverse effect on it." FAA Advisory Circular (AC) 90-23G, "Aircraft Wake Turbulence," discussed aircraft weight categories within the context of ATC separation minima. The AC reiterated the four weight categories described above. The only AC-designated separation criteria discussed in the AC were those for "minimum radar separation;" no explicit wake-separation criteria were presented. The AC included the following two cautionary "Notes": - Whether or not a warning or information has been given, the pilot is expected to adjust aircraft operations and flightpath as necessary to preclude wake encounters. - When any doubt exists about maintaining safe separation distances between aircraft to avoid wake turbulence, pilots should ask ATC for updates on separation distance and groundspeed. FAA Wake Vortex Behavior Information Wake vortices are discussed in AC90-23G and Chapters 4 and 13 of the FAA Pilot's Handbook of Aeronautical Knowledge (PHAK, FAA-H8083-25). According to the PHAK, wing lift generation "triggers the rollup of the airflow aft of the wing resulting in swirling air masses trailing downstream of the wingtips. After the rollup is completed, the wake consists of two counter rotating cylindrical vortices." The strength of the vortex is governed by the weight, speed, and shape of the wing of the generating aircraft. The vortex characteristics of any given aircraft can also be changed by the extension of flaps or other wing configuration devices, as well as by a change in speed. The greatest vortex strength occurs when the generating aircraft is heavy, clean, and slow. The AC stated that the "vortices from an aircraft can pose a hazard to encountering aircraft. For instance, the wake of larger aircraft can impose rolling moments that exceed the roll control authority of smaller encountering aircraft." Wake vortices are rarely detectable visually. The PHAK advised pilots to avoid wake vortex encounters by two principal means: separation by flight path and separation by time. The AC stated that "pilots must learn to envision the location and movements of the vortices generated by other aircraft and to adjust their flightpath accordingly." The guidance provided descriptions of vortex behavior, particularly regarding vertical
The weight shift control aircraft encounter with a wake vortex from a preceding airplane, which resulted in a roll upset at an altitude too low for recovery. Contributing to the accident was the accident pilot's failure to recognize the potential for a wake vortex encounter.
Source: NTSB Aviation Accident Database
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