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General Aviation Safety
On December 7, 2011, about 1630 Pacific standard time, a Sundance Helicopters, Inc., Eurocopter AS350-B2 helicopter, N37SH, operating as a “Twilight tour” sightseeing trip, crashed in mountainous terrain about 14 miles east of Las Vegas, Nevada. The pilot and four passengers were killed, and the helicopter was destroyed by impact forces and postimpact fire. The helicopter was registered to and operated by Sundance as a scheduled air tour flight under the provisions of 14 Code of Federal Regulations (CFR) Part 135. Visual meteorological conditions with good visibility and dusk light prevailed at the time of the accident, and the flight operated under visual flight rules. The helicopter originated from Las Vegas McCarran International Airport, Las Vegas, Nevada, about 1621 with an intended route of flight to the Hoover Dam area and return to the airport. The helicopter was not equipped, and was not required to be equipped, with any on-board recording devices. The accident occurred when the helicopter unexpectedly climbed about 600 feet, turned about 90° to the left, and then descended about 800 feet, entered a left turn, and descended at a rate of at least 2,500 feet per minute to impact. During examination of the wreckage, the main rotor fore/aft servo, one of the three hydraulic servos that provide inputs to the main rotor, was found with its flight control input rod not connected. The bolt, washer, self-locking nut, and split pin (sometimes referred to as a “cotter pin” or “cotter key”) that normally secure the input rod to the main rotor fore/aft servo were not found. The investigation revealed that the hardware was improperly secured during maintenance that had been conducted the day before the accident. The nut became loose (likely because it was degraded)1 and, without the split pin, the nut separated from the bolt, the bolt disconnected, and the input rod separated from the linkage while the helicopter was in flight, at which point the helicopter became uncontrollable and crashed. The NTSB determines that the probable cause of this accident was Sundance Helicopters’ inadequate maintenance of the helicopter, including (1) the improper reuse of a degraded self-locking nut, (2) the improper or lack of installation of a split pin, and (3) inadequate postmaintenance inspections, which resulted in the in-flight separation of the servo control input rod from the fore/aft servo and rendered the helicopter uncontrollable. Contributing to the improper or lack of installation of the split pin was the mechanic’s fatigue and the lack of clearly delineated maintenance task steps to follow. Contributing to the inadequate postmaintenance inspection was the inspector’s fatigue and the lack of clearly delineated inspection steps to follow.
TO THE FEDERAL AVIATION ADMINISTRATION: Encourage operators and manufacturers to develop and implement best practices for conducting maintenance under 14 Code of Federal Regulations Parts 135 and 91 Subpart K, including, but not limited to, the use of work cards for maintenance tasks, especially those involving safety-critical functions, that promote the recording and verification of delineated steps in the task that, if improperly completed, could lead to a loss of control.
Original recommendation transmittal letter:
Closed - Unacceptable Action
Las Vegas, NV, United States
Loss of Control Sundance Helicopters, Inc. Eurocopter AS350-B2, N37SH
Addressee(s) and Addressee Status:
FAA (Closed - Unacceptable Action)
Safety Recommendation History
We note that you do not intend to take the recommended action because you do not believe that generating work cards for Parts 135 and 91 Subpart K would be cost effective. We also note that you plan to continue encouraging Original Equipment Manufacturers to write Instructions for Continued Airworthiness (ICA) to industry-agreed consensus standards and that, once the ICA, with safety-critical steps identified, is provided to an operator, the operator can require documentation of the completion of any safety-critical step in the operator’s maintenance record system. We point out that this proposed process was in place at the time of the accident, and it did not prevent the errors in performance that we identified in our investigation, nor did it ensure the verification of maintenance tasks. This process does not account for previously manufactured aircraft that do not have the support of a current manufacturer, either. Our investigation determined that a work card for the fore/aft servo replacement incorporating Sundance Helicopters’ inspection policy and procedures as described in the company’s general maintenance manual would likely have expanded upon the steps laid out in the aircraft maintenance manual to include separate and distinct verification blocks for each step related to a safety-critical function. We believe that these additional directive aids would have assisted the inspector and the mechanic to help ensure that all steps for a given task had been completed Although we continue to believe that you could improve aviation safety by encouraging Part 135 and 91 Subpart K operations to use work cards, you have stated that you consider your actions complete. Accordingly, Safety Recommendation A-13-2 is classified CLOSED—UNACCEPTABLE ACTION. If you implement, or plan to implement, new processes or procedures that would satisfy this recommendation, please let us know and we will consider reclassifying it.
-From Michael P. Huerta, Administrator: The Federal Aviation Administration (FAA) concurs with the intent of this recommendation and will encourage increasing the control of safety-critical maintenance steps in the following ways: • We will continue to encourage the writing of Instructions for Continued Airworthiness (ICA) to industry-agreed consensus standards. These standards provide specific guidance for the presentation of safety-critical steps. Specifically, FAA Order 8110.54, Chapter 3, Paragraph 2, How to Format ICA, recommends that the Original Equipment Manufacturer propose the format or standard to be used for the writing of maintenance tasks and encourages the use of several industry consensus standards. All of the standards recommended have reasonable systems for identifying safety-critical functions (As an example, see International Specification for Technical Publications Using a Common Source Database standard SIOOOD, Chapter 3.9.3, dealing with "Warnings, Cautions and Notes"). We will also continue to work with industry to maintain and update the consensus standards currently in use; and • Once the TCA for an aircraft is provided to an operator with safety-critical steps identified. the operator(s) would then have a reasonable basis to require documentation of those identified steps. At that point, the operator's manual could then require documentation of the completion of any safety-critical step in their maintenance record system. We have concluded that the intent of this recommendation is better served in other ways than with the recommendation of the use of work cards. Work cards are typically over-burdensome for parts 135 and 91 Subpart K organizations, especially since they are typically seen as only providing significant value for the most commonly performed tasks. ln addition, generating work cards tailored to a specific carrier's operational environment is typically not cost effective for parts 135 and 91 Subpart K organizations. Work cards, as stated in Advisory Circular 120-16F, Air Carrier Maintenance Programs, define the specifics of the task in the context of the maintenance organization accomplishing the task. Where a maintenance manual may say "apply a torque of 100 +/15 ft-lbs," the corresponding work card might instruct a technician recording the actual torque wrench to draw out from a tool crib, as well as company requirements about recording the actual torque, the torque wrench serial number. req uirements for Quality Control on the torque. how to record the paperwork associated with the task, and so on. In general, work cards are employed in the air carrier environment to make things simpler (and by extension, quicker and less error-prone) for floor-level technicians. For this reason, we can, and will, encourage the use of work cards where appropriate. However, we do not feel there will be a significant acceptance rate for the use of work cards within the parts 135 and 91 Subpart K communities. I believe that the FAA has addressed this safety recommendation and consider our actions complete.
We look forward to learning the results of the FAA’s review and determination of the most feasible course of action to address Safety Recommendation A-13-2. Pending our review of those results and completion of the recommended action, this recommendation is classified OPEN—ACCEPTABLE RESPONSE.
-From Michael P. Huerta, Administrator: The FAA will review the current recommendation and determine the best feasible course of action to encourage operators and manufacturers to develop and implement best practices for conducting maintenance under parts 135 and 91 Subpart K. I will keep the Board informed of the FAA's progress on this recommendation and provide an update by May 2014.
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