Seattle, WA, USA
N250FB
EUROCOPTER AS 350 B2
The pilot was repositioning the helicopter from a rooftop helipad where it had just been refueled to a nearby airport. Video footage revealed that the helicopter lifted off of the helipad and simultaneously started to yaw to the left, consistent with a loss of tail rotor control. The helicopter completed one 360-degree rotation about the yaw (vertical) axis in a near level attitude while climbing. As it continued to rotate (spin) to the left, the helicopter deviated from a level attitude, pitching nose down and banking right, consistent with a loss of main rotor control. The helicopter moved away from the helipad, lost altitude, and impacted the street below. A postcrash fire erupted that consumed most of the fuselage and the forward section of the tailboom. All major structural components of the helicopter were found at the accident site, and there was no evidence of an inflight failure of the airframe. Examination of the engine revealed that it was producing power at the time of impact. Further, the main rotor and tail rotor systems exhibited damage consistent with powered impact. Flight control continuity could not be confirmed due to fire and impact damage, and most components of the hydraulic system were severely fire damaged or destroyed preventing determination of their preimpact condition. The NTSB determined that the loss of tail rotor and main rotor control resulted from a loss of hydraulic boost. This determination was made based on a series of deductions. A helicopter can enter a left yaw at takeoff for one of three reasons: 1) a loss of tail rotor effectiveness, 2) a loss of tail rotor drive, or 3) a loss of tail rotor control. In this accident, a loss of tail rotor effectiveness was unlikely because the reported wind speeds at nearby airports at the time of the accident were 4 knots or less. A loss of tail rotor drive was ruled out in this case based on the physical evidence indicating that the tail rotor was powered at ground impact. Thus, the left yaw at takeoff was likely due to a loss of tail rotor control. A loss of tail rotor control can result from one of three circumstances: 1) a disconnect in the tail rotor pedal control system; 2) a restriction or jam in the pedal controls, or 3) a loss of hydraulic boost to the pedal controls. Although either a disconnect or a restriction/jam in the pedal controls would explain the helicopter's left yaw at takeoff, neither would explain the rapid loss of pitch and bank (main rotor) control that occurred after the first 360-degree yaw rotation that appears consistent with a loss of hydraulic boost to the main rotor controls. Therefore, a loss of hydraulic boost to the pedal controls, followed by a loss of hydraulic boost to the main rotor controls, most likely occurred. The NTSB then evaluated scenarios that may have led to the complete loss of hydraulic boost to the main and tail rotor controls during takeoff. These scenarios include the following, with the last being the most likely, as described below: Scenario 1 – Loss of hydraulic pressure due to mechanical failure and simultaneous failure of the yaw load compensator. In this scenario, a loss of pressure to the hydraulic system would result in the loss of hydraulic boost to the main and tail rotor servo controls. The yaw load compensator would provide partial hydraulic boost to the pedal controls unless the compensator failed, which would result in no hydraulic boost to the pedal controls. Because the yaw load compensator would likely have been functionally checked during the preflight hydraulics check, this scenario is considered unlikely because of the low probability of two separate failures occurring simultaneously. Scenario 2 – A misconfiguration of the hydraulic system at the conclusion of the preflight hydraulic system checks. In this scenario, the pilot would have performed the preflight hydraulic system checks but would have failed to reset the "HYD TEST" button, the hydraulic cut-off switch, or both, at the end of the preflight hydraulic system checks. The accumulator check, which requires the pilot to activate and then reset the "HYD TEST" button, is the first of the two preflight hydraulic system checks. Activating the "HYD TEST" button depressurizes the main and tail rotor servo controls, depletes the yaw load compensator, but does not deplete the main rotor accumulators. The hydraulic cut-off test, which activates and then resets the hydraulic cut-off switch, is the second of the two preflight hydraulic system checks. Activating the hydraulic cut-off switch depressurizes the main and tail rotor servo controls, depletes the main rotor accumulators, but does not depressurize the yaw load compensator. The preflight hydraulic system checks require the pilot to visually confirm that the "HYD" warning light turns off after completion of each check, and this light would have remained illuminated had either or both the "HYD TEST" button and hydraulic cut-off switch not been reset by the pilot. Unless the pilot was performing the preflight hydraulic checks via tactile feel of the controls alone, without visual confirmation of the "HYD" warning light on the caution-warning panel, and did not verify all caution and warning lights were extinguished before takeoff, as required by the flight manual, the scenario of a misconfigured hydraulic system at the conclusion of the preflight hydraulic checks is unlikely. Scenario 3 – Loss of pressure during the preflight hydraulic system accumulator check due to activation of the "HYD TEST" button combined with an unlocked collective stick. In this scenario, the pilot would have engaged the "HYD TEST" button and then moved the cyclic control stick to verify that the main rotor accumulators were functioning properly. If the collective stick was not locked during this check and one or more of the main rotor accumulators were depleted by the cyclic movements, the collective would have moved up rapidly. This uncommanded collective movement is caused by a design characteristic of the main rotor system in the AS350 helicopter. The uncommanded movement is prevented by engaging the collective lock as specified in the preflight checklist. Although accidents have occurred in which an unsecured collective stick moved up enough to cause an inadvertent liftoff (see NTSB accident investigations LAX01LA083 and LAX02TA299), postaccident ground testing with an exemplar helicopter showed that, at its estimated takeoff weight, the accident helicopter would not have become airborne or light on its skids due to uncommanded collective movement as a result of main rotor accumulator depletion alone. Revision 3 of the AS350-B2 rotorcraft flight manual indicated that the preflight hydraulic system checks were to be conducted with the fuel flow control lever (FFCL) set between the "OFF" and "FLIGHT" detents. The pilot was trained in this procedure. During the ground tests, no heave (upward movement) was felt during the tests conducted with the FFCL set properly between the "OFF" and "FLIGHT" detents. However, the operator's checklist, which was likely used by the pilot, specified that the FFCL be set to the "FLIGHT" detent (a higher power setting) during the preflight hydraulic system checks. During the ground tests with the FFCL in the "FLIGHT" detent, when the collective moved up, a heave was felt by the occupants of the exemplar helicopter. If the pilot did not lock the collective and performed the accumulator check with the FFCL in the "FLIGHT" detent per the operator's checklist, he may have been startled by an uncommanded increase in collective and the accompanying heave. The pilot may have reacted by manually increasing collective pitch, resulting in an unplanned takeoff. Once airborne, the lack of hydraulic boost to the pedals would have resulted in an uncontrolled left yaw, and, as all three main rotor accumulators became depleted, the main rotor controls would have lost hydraulic boost, resulting in a rapid loss of control. This scenario best matches the video evidence. Because scenarios 1 and 2 are considered unlikely, scenario 3 is left as the most likely scenario for this accident. However, because of the damage to the hydraulic system components and because the helicopter was not equipped with any type of flight recording device, no determination could be made regarding the pilot's actions during performance of the preflight hydraulic checks or regarding the hydraulic system configuration when the helicopter became airborne. If a recorder system that captured cockpit audio, images, and parametric data had been installed, it would likely have enabled reconstruction of the sequence of events leading to the loss of control.
***This report was modified on November 24, 2015, and September 6, 2016. Please the docket for this accident to view the original report.*** HISTORY OF FLIGHT On March 18, 2014, about 0738 Pacific daylight time (PDT), an Airbus Helicopters (formerly Eurocopter) AS 350 B2, N250FB, was destroyed when it impacted terrain following takeoff from the KOMO TV Heliport (WN16), Seattle, Washington. The helicopter was registered to, and operated by, Helicopters Incorporated, Cahokia, Illinois, under the provisions of Title 14 Code of Federal Regulations Part 91. The commercial pilot and one passenger were fatally injured, and one person, located in a stationary vehicle, was seriously injured. Visual meteorological conditions prevailed, and no flight plan was filed for the local repositioning flight, which was originating at the time of the accident. The pilot's intended destination was the Renton Municipal Airport (RNT), Renton, Washington. The Electronic News Gathering (ENG) equipped helicopter had landed on the KOMO News helipad about 30 minutes prior to the accident. The purpose was to refuel for its repositioning flight to RNT. A witness who was located on the south side of the helipad reported that he observed the helicopter initially lift off of the helipad to about 15 ft, followed by a muffled sound like a car backfiring. The witness opined that after lifting off it immediately pointed nose up, and began rotating counter-clockwise, after which it rotated out of sight. A second witness, who was stationed in a crane a few hundred feet to the northeast of the helipad, reported that he observed the helicopter lift up off of the helipad, turn toward the west, and then shot straight back with its nose up, and out of control. It then nosed down into the street below. The helicopter descended into an occupied automobile near a main street intersection, after which a postimpact fire ensured. During the investigation, a review of three security camera recordings, which were provided to the National Transportation Safety Board (NTSB) investigator-in-charge (IIC) by the Seattle Police Department, revealed that the helicopter initially landed on the helipad, and remained stationary for about 15 minutes. The helicopter lifted off and simultaneously began to rotate counter-clockwise in a near level attitude. The helicopter continued to rotate counter-clockwise for about 180 degrees while it ascended slightly above the elevated helipad, after which it began to ascend further while moving slightly away from the elevated helipad. After the helicopter completed about a 360-degree rotation, the helicopter transitioned to a nose-low (tail-high) attitude while it continued to rotate counter-clockwise. The helicopter rotated counter-clockwise another 180 degrees, and then began to lose altitude while moving rapidly away from the elevated helipad. The helicopter then descended until ground impact. Examination of the accident site revealed that the helicopter came to rest on its right side, oriented on a magnetic heading of about 050 degrees. A vehicle located east of the main wreckage was fire damaged. Another vehicle, which was located immediately west of the main wreckage and oriented on a southerly heading, exhibited impact damage. All major structural components of the helicopter were located in the immediate area of the main wreckage. Wreckage debris was located within an approximate 340 foot radius to the main wreckage. The helicopter was recovered to a secured location for further examination. PERSONNEL INFORMATION Pilot in Command General The pilot, age 59, possessed a commercial pilot certificate with a helicopter instrument rating. He also held a helicopter flight instructor certificate with an instrument helicopter rating. His most recent second-class medical certificate was issued on February 6, 2014, with the limitation, "Must wear corrective lenses and possess glasses for near and intermediate vision." The pilot successfully completed his most recent flight review in the accident helicopter on February 8, 2014. A review of the pilot's personal pilot logbooks revealed that as of February 7, 2014, he had accumulated a total flight time of 6,538.8 hours, all in rotorcraft-helicopters. Additionally, the pilot had accumulated 6,295.5 hours as pilot-in-command, 2,841 hours of instruction given, 1,047 hours in the Airbus AS350-D, and about 5.5 hours in the Airbus AS350-B2 helicopter. Additionally, the pilot had logged 1,122 hours in the Bell 206 helicopter, and a total of 1,092 hours flight time in the Bell 407. A family member revealed during an interview with NTSB investigators that the pilot worked part time as an ENG pilot on the early morning shift. He would normally awaken between 0300 and 0400, and report for work at 0500, normally Monday thru Friday, but sometimes on weekends if there was a need. He would normally return home from his full time job as an engineer for a local airplane manufacturing company, and predictably go to bed at 2000. The family member said that the pilot was in excellent health, had no sleep disorders, and had performed this schedule for many years. Additionally, the family member opined that the pilot was looking forward to flying full time after retiring from his full time job. Pilot's ENG Operational Experience A further review of the pilot's recorded personal logbook entries revealed that he had started ENG flight operations in a Bell 206 on May 30, 2002, accumulating a total of 1,090 hours in this make and model helicopter, prior to transitioning to the Airbus AS350-D model on August 16, 2004. The pilot then operated this make and model helicopter in ENG operations until July 9, 2008, having accumulated a total time of 1,047 hours in the AS350-D. Prior to concluding ENG flight operations in the AS350-D during July 2008, the pilot received Bell 407 transition training with Bell Helicopters on April 26, 2006. The pilot then flew the Bell 407 on a limited basis from August, 2006 to January 2008, accumulating a total of about 24 hours of flight time during this period. On January 21, 2008, the pilot attended Bell 407 recurrent training, having received 2.5 hours of flight training. The pilot subsequently began flying the Bell 407 helicopter in ENG flight operations on March 24, 2008, with his last flight logged in this make and model helicopter on February 7, 2014. At this time, the pilot had accumulated a total flight time of 1,092 hours in the Bell 407. Pilot's Airbus AS350 B2 Training According to Helicopters Incorporated personnel, the accident helicopter arrived at the company's Renton base of operations on January 30, 2014. The helicopter had been ferried from St. Louis, Missouri, to Renton by a part time company Check Airman, and the Renton based pilot who shared flying duties with the accident pilot; this pilot normally flew the afternoon shift, relieving the accident pilot about 1000. According to training records supplied to the NTSB IIC at the request of Helicopters Incorporated, the pilot began Airbus AS350-B2 training January 31, the day after the helicopter arrived at the Renton base. At this time the Check Airman gave the pilot 0.5 hours of recurrent training. Subsequently, on February 8, the accident pilot received an additional 3.0 hours of flight instruction, which was inclusive of a check ride. The pilot satisfactorily passed the check ride, as well as the Airbus AS350 limitations written test. The pilot next flew the accident helicopter on the day of the accident, March 18, which would have been 39 days after his most recent flight in the helicopter. Airbus AS350 B2 Checklists Used During Training During the postaccident examination of the helicopter, inclusive of the onsite and follow-up layout examinations, the helicopter's checklist was not observed. In several discussions with the Helicopters Incorporated Assistant Director of Operations and the company's Director of Safety, it was frequently stated that the Abbreviated Checklist for the AS350 BA/B2, Revision 1 (an internal document), dated June 30, 2009, which was a two-sided laminated checklist with a Federal Aviation Administration (FAA) Approved Date of August 20, 2009, and signed by an FAA inspector assigned to the St. Louis (STL) Missouri Flight Standards District Office, had been delivered with the helicopter when it arrived at the Renton base. Additionally, the Renton-based pilot (who had ferried the helicopter from St. Louis to Renton with the part-time company Check Airman, when interviewed by the NTSB IIC and asked which checklist would have been in the helicopter at the time of the accident), revealed that it was a two-sided, laminated checklist, and that it had an FAA approved stamp on it. At the time of the accident, the most current revision to the AS350-B2 Rotorcraft Flight Manual (RFM) was Revision 4, dated the 11th week of year 2010. Revision 3, dated the 21st week of year 2006, contained changes to Paragraph 3 ("Starting") of Section 4.1 ("Operating Procedures") to set the fuel flow control lever (FFCL) to a position between the "OFF" and "FLIGHT" detents in order to achieve a gas generator speed (Ng) of between 67-70% before performing the hydraulic system checks. According to the airframe manufacturer, an Ng of 67-70% will result in a corresponding main rotor speed (Nr) of about 270 rotations per minute (RPM). According to the RFM, 100% Nr on the ground at low pitch is between 375-385 RPM. The previous procedure (Revision 2 and prior) was to set the FFCL to the "FLIGHT" detent, about 82% Ng, resulting in 100% Nr, prior to performing the hydraulic system checks. According to the airframe manufacturer, the change to the starting procedures in the RFM was a result of several events where the helicopter became unintentionally airborne due to the collective stick becoming unlocked during the hydraulic system checks. By performing the hydraulic system checks at 67-70% Ng, the helicopter should not become airborne if the collective stick was not locked, or becomes unlocked during the hydraulic system checks. According to the airframe manufacturer, six copies of Revision 3 to the RFM were mailed to the operator on May 12, 2010. However, there was no evidence that the previous edition of the checklist, the Abbreviated Checklist dated June 30, 2009, had been revised to reflect the lower Ng setting prior to conducting the hydraulic system checks. When the part-time Check Airman, who provided the recurrent flight training for the accident pilot was asked during a meeting of parties to the investigation on May 22, 2014, which checklist he used during training, the Check Airman stated that he used the procedures that were outlined in Revision 3 of the RFM. Additionally, the Check Airman stated that he had instructed both the accident pilot and the second pilot who shared the local ENG duties with the accident pilot, to use the procedures outlined in Revision 3 of the RFM (Ng of 67-70%). In addition, an FAA inspector recalled that during the conference meeting, the Check Airman mentioned that the checklist used had the hydraulic checks being conducted with the engine throttle in the Flight Gate (Ng about 82%). Further, the Check Airman stated that after Revision 3 became active, he notified the operator's Chief Pilot of the change to the Ng setting prior to performing the hydraulic system checks; however, the checklist in use at the time was not revised. The operator opined that the Abbreviated Checklist was neither revised nor removed from their AS350 B2 fleet as a result of an oversight. When the part time Check Airman, who provided the recurrent flight training for the accident pilot was asked several weeks after his initial statement to the investigative team on May 22, 2014, if he remembered if the Abbreviated Checklist was in the accident helicopter, either during the ferry flight to Renton from St. Louis, or during the training he conducted after he had arrived back to the Renton base following the ferry flight, he said that he could not recall. AIRCRAFT INFORMATION General The helicopter, an Airbus Helicopters AS350-B2, serial number (S/N) 3669, was equipped with a Turbomeca Arriel 1D1 engine. A review of the maintenance records revealed that the helicopter had accumulated a total time of 7,706.5 hours at the time of the accident. Additionally, the engine, S/N 9849, had accumulated 7,122.9 hours since new, and 538 hours since it last overhaul. Maintenance According to the operator, the helicopter was maintained in accordance with the Manufacturer's Inspection Program. On March 13, 2014, at an aircraft total time (ATT) of 7,698.5 hours, the most recent inspection was performed and documented per a Maintenance Log Entry. The inspection revealed the following: • a 30-hour check of the tail rotor blades in accordance with (IAW) Chapter 64-10 of the Eurocopter Airworthiness Limitations Section, Rev. 004, dated June 6, 2013, with no defects noted. • Complied with Eurocopter Alert Service Bulletin 05.00.60, Rev. 0, tail rotor pitch change links check, with no defects noted. • Complied with Airworthiness Directive (AD) 2011-22-05, inspection of tail rotor pitch change links, with no defects noted. • Performed 30-hour engine inspection IAW Turbomeca Arriel 1D1 Maintenance Manual, update #17, dated October 30, 2013, with no defects noted. • Complied with AD 2003-02-05, Sliding Door Rail Inspection, with no defects noted. • Complied with Eurocopter Alert Service Bulletin 05.00.74 Rev. 1, Tail Rotor Pitch Horn Inspection, with no defects noted. • Complied with 100-hour inspection items that have no margin in the Eurocopter Airworthiness Limitations Section 04-20-00, Rev. 4 dated June 6, 2013, with no defects noted. This was accomplished in order to extend the 100-hour inspection by using the 10-hour tolerance. On March 5, 2014, at an ATT of 7,676.1 hours, the operator complied with FAA Airworthiness Directive (AD) No. 2014-02-05, a recurrent inspection of the clearance between the main rotor collective control lever and the collective locking stud. The AD specifically defined an unsafe condition as the main rotor collective pitch lever (collective) locking stud inadvertently locking in the low pitch position, which could result in a subsequent loss of control of the helicopter. (Refer to the AD, which is appended to the docket for this report.) On March 29, 2012, at an ATT of 6,548.0 flight hours and a component total time (CTT) of 6,007.0 hours, a tail rotor servo control, S/N 1298, was installed on the accident helicopter. The tail rotor servo control was overhauled on February 21, 2012 by UTAS in Vernon, France. COMPANY OVERVIEW The operator of the helicopter, Helicopters Incorporated, was founded in 1978 by a private individual. As of August 14, 2014, it was reported that the company operated more than 70 ENG helicopters in 36 markets nationwide. In calendar year 2013, the company flew over 35,000 hours in support of ENG operations. The company's organization consists of the following: • Director of Operations • Assistance Director of Operations • Chief Pilot • Director of Maintenance • Director of Safety • ADPM & Security Coordinator The company's employment base consisted of the following: • Pilots – 149 • Maintenance support personnel – 49 • Total employees – 285 The company's complement of aircraft/helicopters includes the following: • Bell 206B – 24 • Bell 206L3 – 2 • Bell 206L4 – 26 • Bell 407 – 11 • Airbus AS350BA – 3 • Airbus AS350B2 – 6 • Airbus AS350B3 – 1 Total number of aircraft – 73 AERODROME INFORMATION WN16 was activated on May 1982. The address of the heliport was 100 4th Avenue North, Seattle, Washington, and was located at coordinates 47 degrees, 37.30 minutes north latitude and 122 degrees, 20.68 minutes west longitude. The estimated elevation above mean sea level (msl) was reported as 363 feet. The height above the street level where the helicopter came to rest was about 85 ft. The operational surface area of the heliport, constructed of concrete, was about 65 feet in diameter. The heliport incorporated edge lighting around its perimeter. It als
The loss of helicopter control due to a loss of hydraulic boost to the tail rotor pedal controls at takeoff, followed by a loss of hydraulic boost to the main rotor controls after takeoff. The reason for the loss of hydraulic boost to the main and tail rotor controls could not be determined because of fire damage to hydraulic system components and the lack of a flight recording device.
Source: NTSB Aviation Accident Database
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