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On July 3, 2015, about 1339 mountain daylight time, an Airbus Helicopters AS350 B3e helicopter, N390LG, registered to and operated by Air Methods Corporation, lifted off from the Summit Medical Center Heliport, Frisco, Colorado, and then crashed into a parking lot; the impact point was located 360 feet southwest of the ground-based helipad. The pilot was fatally injured, and the two flight nurses were seriously injured. The helicopter was destroyed by impact forces and a postcrash fire. The flight was conducted under the provisions of 14 Code of Federal Regulations Part 135 on a company flight plan. Visual meteorological conditions prevailed at the time of the accident.
TO AIRBUS HELICOPTERS: For newly manufactured dual-hydraulic AS350-series helicopters, assess and implement changes to the dual hydraulic system that would both ensure pedal control hydraulic assistance and mitigate the possibility of pilot error during any check of the hydraulic system.
Original recommendation transmittal letter:
Open - Acceptable Response
Frisco, CO, United States
Aircraft Accident Report: Loss of Control at Takeoff Air Methods Corporation Airbus Helicopters AS350 B3e, N390LG
Addressee(s) and Addressee Status:
Airbus Industrie (Open - Acceptable Response)
Safety Recommendation History
The National Transportation Safety Board (NTSB) has reviewed the Federal Aviation Administration’s (FAA) notice of proposed rulemaking (NPRM) titled, “Airworthiness Directives; Airbus Helicopters,” which was published at 82 Federal Register 42487 on September 8, 2017. The NPRM proposes to adopt a new airworthiness directive (AD) for Airbus Helicopters model AS350B3 helicopters with a dual hydraulic system installed. The proposed AD would supersede AD 2015-22-53, retaining its requirements while also mandating incorporation of a caution light when the yaw servo hydraulic switch is in the OFF position, as well as a monostable (push on, timer off) ACCU TST button. We are pleased that the proposed AD would require a modification to the ACCU TST push button such that it would automatically reset after activation, which would reduce the possibility of pilot error in forgetting to reset it while performing a check of the yaw load compensator. However, the NTSB notes that, while the proposed AD would mandate changes to improve pilots’ awareness of the position of the yaw servo hydraulic switch, the changes do not address the need for an alert when there is insufficient pressure in the tail rotor hydraulic circuit, which would lead to increased pedal loads. The NTSB believes that, for at least four events we’ve investigated in which the yaw servo hydraulic switch likely was not returned to its correct (ON) position before takeoff, a salient alert could have cued the pilots to insufficient hydraulic pressure in the tail rotor hydraulic circuit. This is a deficiency we also noted in our January 14, 2016, comments on AD 2015-22-53 and discussed in the Frisco, Colorado, accident report. As a result of that investigation, the NTSB issued Safety Recommendation A-17-8, which calls for both an aural and visual indication of a loss of hydraulic boost to the pedal controls. The proposed AD would not satisfy the intent of this recommendation. Further, the NTSB remains concerned that the proposed AD intends to retain the changes implemented by AD 2016-22-53 in still requiring a functional check of the yaw load compensator—which could be used during a critical situation during flight—as a postflight procedure. (Before AD 2016-22-53, the functional check of the yaw load compensator was performed during the preflight run-up procedures.) A postflight check of the yaw load compensator does not completely eliminate the risk of taking off without backup hydraulic boost to the pedals because the postflight check does not ensure that the yaw load compensator will remain functional for the next flight. This concern was the basis for issuing Safety Recommendations A-17-9 and 10 to Airbus Helicopters in connection with the Frisco, Colorado, accident investigation. In response to these recommendations, Airbus Helicopters stated that it is considering design revisions of the dual hydraulic system that may satisfy the recommendations and may result in revisions to the rotorcraft flight manual procedures that would address the NTSB’s concerns about performing the yaw load compensator check as a postflight procedure. We appreciate the opportunity to comment on this NPRM.
We are aware of the items listed in Mr. Dumont’s letter that have already been completed; we discussed them in our report about the accident in Frisco, Colorado. These items address mitigating the possibility of pilot error during a hydraulic system check, but they do not ensure that pedal control hydraulic assistance remains available during helicopter operation. We point out that these recommendations ask you to address both issues simultaneously. We note that you are exploring several options to further improve the dual hydraulic system, including adding a system allowing the yaw load compensator accumulator pressure to be checked. We emphasize that, for a solution to satisfy these recommendations, it will need to address both ensuring pedal control hydraulic assistance and mitigating pilot error during a system check; and, as discussed in our report, if the revised design continues to use a yaw load compensator requiring a functional check to ensure it provides backup hydraulic assistance to the pedal controls, the check needs to be done before the flight, not after. Pending revisions to the hydraulic system as recommended, Safety Recommendations A-17-9 and -10 are classified OPEN--ACCEPTABLE RESPONSE.
-From Jean-Brice DUMONT, Executive Vice-President Engineering, Airbus Helicopters: Airbus Helicopters has carefully reviewed these recommendations and would like to stress that it considers to have already addressed the subject with: the introduction of a light "HYD" warning for both hydraulic circuits ("HYD 1" and "HYD 2") and a flashing mode of the light "HYD 2" warning if the yaw servo hydraulic switch is not in the normal « ON» position through the modification 07.4622 (applicable on new aircraft produced since April 2014 and available for retrofit through SB No. AS350-67.00.64 since February 2015). This modification was considered as a safety barrier before the replacement of the yaw load compensator pre-flight check by a post-flight check through SB n° AS350-67.00.66 the replacement of the yaw load compensator pre-flight check procedure by a post flight check procedure (SB No AS350-67.00.66 and associated SIN No 2944-S-29 released on August 2015) mandated by EASA AD n° 2015-0178 dated August 2015 and FAA AD n° 2015-22-52/53 dated October 2015 the issuing of the SIN No 2992-S-OO (January 2016) reminding to perform a hover during the take-off phase as requested by the flight manual procedure and compliant with the content of the FAA SAFO n° 16016 published November 2016 the introduction of the monostable pushbutton through the modification 07.4719 (Application on new aircraft since June 2016 and available for retrofit through SB No AS350-67.00.65 since August 2016). All these actions/modifications have introduced some additional safety barriers reducing again the possibility of a pilot error before departure and informing the pilot about the condition of the hydraulic circuit: No longer necessary to manipulate the Yaw Servo Hydraulic Switch during the run-up hydraulic checks I starting Procedure (first safety barrier resulting from the application of SB N° AS350-67.00.66) Require to check the correct position of the Yaw Servo Hydraulic Switch prior to engine starting and prior to take-off (Second safety barrier resulting from the application of SB N° AS350-67.00.66) Remind that the FLM request to gradually increase collective to a hover at 5ft and to check in this hover flight engine and mechanical parameters as well as absence of any warning lights (third safety barrier reminded through SIN 2992-S-OO and FAA SAFO 16016) MOD 07.4622 =safety improvement to alert the pilot in case of an abnormal position of the Yaw Servo Hydraulic switch before flight MOD 07.4719 =safety improvement to avoid the possibility to forget to reactivate the "HYO TEST/ACCU TST" push button during the post flight test All these actions/modifications have been reminded to all operators in the Light Helicopters Information Letter (LH 017-2016) released in July 2016. Furthermore the EASA has issued an AD n° 2016-0220 dated November 2016 mandating the application of the MOD 07.4622 and 07.4719 to cover a crew human factor error. Even if safety is fully ensured by the measures listed above, Airbus Helicopters is exploring several options to further improve the dual hydraulic system. One of the options could be the addition of a system allowing checking the pressure of the yaw load compensator accumulator. This option would have the following advantages: It would allow replacing the present functional check of the yaw load compensator performed by the previous flight pilot by a visual check on the ground before the flight performed by the flying pilot. It would comfort the flying pilot of the good operation of the yaw load compensator which will have a proven performance in case of hydraulic failure on the tail rotor circuit. It would allow providing a retrofittable solution for the in-service dual hydraulic AS350 series and even in a next step for the single hydraulic AS350 series. The analysis of this modification in terms of feasibility, efficiency and consequence on aircraft is ongoing and we will keep you informed of the progress of this option in due time.
On March 28, 2017, we adopted our report concerning the July 3, 2015, accident in which an Airbus Helicopters AS350 B3e helicopter, N390LG, registered to and operated by Air Methods Corporation, lifted off from the Summit Medical Center Heliport, Frisco, Colorado, and then crashed into a parking lot; the impact point was located 360 feet southwest of the ground-based helipad.1 Additional information about this accident and the resulting recommendations may be found in the report of the investigation, which can be accessed at our website, http://www.ntsb.gov, under report number NTSB/AAR-17/01. As a result of this investigation, we issued six new recommendations, including one to the Federal Aviation Administration (FAA), one to the FAA and the European Aviation Safety Agency, one to the Association of Critical Care Transport, one to the Association of Air Medical Services and the Air Medical Operators Association, and the following two recommendations to Airbus Helicopters.
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