AEROSPATIALE AS350BAHeli-USA Airways, Inc.
Princeville, HI, USA · 2007-03-09·N354NT
What happened
NTSB summary, verbatimThe helicopter was returning from a sightseeing flight when the pilot contacted the dispatcher and announced, "I'm having hydraulic problems, and I'm probably going to have to do a run-on landing." The language he used to describe his situation changed from "hydraulic problem" to "hydraulic failure" as the flight proceeded. The pilot did not immediately land at the approach end of the runway; instead, he continued to the departure end, where the passenger terminal was located. The helicopter approached the mid-point of the runway, and as it neared the surface, the dispatcher heard the pilot state, "Okay we're done." Then, the sound of the rotor changed pitch and the helicopter impacted the ground. Postaccident examination of the helicopter revealed that the left lateral flight control servo became disconnected in flight at the transmission. Further examination revealed that the lower clevis of the left lateral servo was still attached to the transmission case, but was no longer attached to the servo. The threads on the clevis, as well as the threads on the inner diameter of the servo, appeared undamaged. The jam nut, lock nut washer, and safety wire were still attached to the clevis threads and rotated freely. The lock washer was severely worn and the locking tang was missing. Metallurgical testing and torque testing of the accident servos revealed that the jam nut, washer, and piston rod were able to easily rotate off of the clevis if no torque was applied and with the locking tang missing. Under normal loads, the main hydraulic flight control servos experience slight twisting that could contribute to the servo rotating off the clevis bolt (without an intact and functioning locking washer installed). Therefore, the investigation revealed that the servo attachment nut was not torqued during maintenance about one month prior to the accident, and the lack of torque, coupled with the installation of a severely worn lock washer, allowed the servo to rotate off of the clevis during the accident flight, resulting in a complete disengagement of the servo from its mounting clevis on the transmission. Examination of the company maintenance program revealed that none of the mechanics at the helicopter's base had received factory training, and that the maintenance manuals they used were three revisions out of date. Mandatory quality control inspections of maintenance actions, as well as post-maintenance test flights prescribed in the General Operator's Manual and the manufacturer's maintenance manuals (that included the replacement of the flight control servo), were not performed. (This report was modified on June 16, 2009)
Probable cause
the Board's determinationThe failure of maintenance personnel to properly tighten (torque) the flight control servo lower attachment clevis, and reinstall a functioning lock washer, which resulted in a flight control disconnect and a complete loss of helicopter control. Contributing to the accident was the operator's failure to ensure its maintenance program was being executed in accordance with Federal regulations.
Safety recommendations
12 issuedwhat changed because of this accidentTO THE FEDERAL AVIATION ADMINISTRATION: Require that all air tour operators (14 Code of Federal Regulations Parts 91 and 135) establish and maintain a system for continuously analyzing the performance and effectiveness of their inspection and maintenance program to ensure that all maintenance is performed with the utmost regard for quality and safety.
TO THE FEDERAL AVIATION ADMINISTRATION: Require air tour operators to provide formal, model-specific helicopter maintenance training for their mechanics to ensure an adequate level of competency.
TO THE FEDERAL AVIATION ADMINISTRATION: Develop a mechanism to provide direct surveillance of air tour maintenance at all locations where a company’s maintenance is conducted.
TO THE FEDERAL AVIATION ADMINISTRATION: Work with independent safety programs, such as the Tour Operators Program of Safety, to establish appropriate guidance for their members on how to develop and implement appropriate inspection and maintenance quality assurance programs and to encourage operators to participate in these voluntary programs.
TO THE TOUR OPERATORS PROGRAM OF SAFETY: Coordinate with Tour Operators Program of Safety members to set requirements for establishing and maintaining a system for continuously analyzing the performance and effectiveness of their inspection and maintenance programs to ensure that all maintenance is performed with the utmost regard for quality and safety.
TO THE TOUR OPERATORS PROGRAM OF SAFETY: Expand the Tour Operators Program of Safety’s safety audit program to ensure that operators implement an effective maintenance quality assurance program.
TO THE TOUR OPERATORS PROGRAM OF SAFETY: Work with the Federal Aviation Administration to establish appropriate guidance for Tour Operators Program of Safety members on how to develop and implement appropriate inspection and maintenance quality assurance programs.
TO THE TOUR OPERATORS PROGRAM OF SAFETY: Coordinate with Tour Operators Program of Safety (TOPS) members to establish requirements for providing formal, model-specific helicopter maintenance training for their mechanics to ensure an adequate level of competency. Once requirements are established, examine members’ maintenance education programs during TOPS’ annual audit.
TO THE FEDERAL AVIATION ADMINISTRATION: Require Eurocopter to identify AS-350 and EC-130 helicopter hydraulic pump drive shafts and coupling sleeves with splines that do not meet design specifications and take appropriate action to ensure that these parts (that is, replacement parts and parts to be installed in new helicopters) are expeditiously removed from the supply chain.
TO THE FEDERAL AVIATION ADMINISTRATION: Require operators of Eurocopter AS-350 and EC-130 helicopters to perform a wear check, visual inspection, and lubrication of the hydraulic power assembly splines and coupling sleeve splines in accordance with the latest version of the maintenance manual at the earliest opportunity, and, thereafter, require operators to repeat the wear check, visual inspection, and lubrication of the splined connection at 100-hour intervals, and remove unairworthy parts from service.
TO THE EUROPEAN AVIATION SAFETY AGENCY: Require Eurocopter to identify AS-350 and EC-130 helicopter hydraulic pump drive shafts and coupling sleeves with splines that do not meet design specifications and take appropriate action to ensure that these parts (that is, replacement parts and parts to be installed in new helicopters) are expeditiously removed from the supply chain.
TO THE EUROPEAN AVIATION SAFETY AGENCY: Require operators of Eurocopter AS-350 and EC-130 helicopters to perform a wear check, visual inspection, and lubrication of the hydraulic power assembly splines and coupling sleeve splines in accordance with the latest version of the maintenance manual at the earliest opportunity, and, thereafter, require operators to repeat the wear check, visual inspection, and lubrication of the splined connection at 100-hour intervals, and remove unairworthy parts from service.
NTSB analysis
from the final reportThe helicopter was returning from a sightseeing flight when the pilot contacted the dispatcher and announced, "I'm having hydraulic problems, and I'm probably going to have to do a run-on landing." The language he used to describe his situation changed from "hydraulic problem" to "hydraulic failure" as the flight proceeded. The pilot did not immediately land at the approach end of the runway; instead, he continued to the departure end, where the passenger terminal was located. The helicopter approached the mid-point of the runway, and as it neared the surface, the dispatcher heard the pilot state, "Okay we're done." Then, the sound of the rotor changed pitch and the helicopter impacted the ground. Postaccident examination of the helicopter revealed that the left lateral flight control servo became disconnected in flight at the transmission. Further examination revealed that the lower clevis of the left lateral servo was still attached to the transmission case, but was no longer attached to the servo. The threads on the clevis, as well as the threads on the inner diameter of the servo, appeared undamaged. The jam nut, lock nut washer, and safety wire were still attached to the clevis threads and rotated freely. The lock washer was severely worn and the locking tang was missing. Metallurgical testing and torque testing of the accident servos revealed that the jam nut, washer, and piston rod were able to easily rotate off of the clevis if no torque was applied and with the locking tang missing. Under normal loads, the main hydraulic flight control servos experience slight twisting that could contribute to the servo rotating off the clevis bolt (without an intact and functioning locking washer installed). Therefore, the investigation revealed that the servo attachment nut was not torqued during maintenance about one month prior to the accident, and the lack of torque, coupled with the installation of a severely worn lock washer, allowed the servo to rotate off of the clevis during the accident flight, resulting in a complete disengagement of the servo from its mounting clevis on the transmission. Examination of the company maintenance program revealed that none of the mechanics at the helicopter's base had received factory training, and that the maintenance manuals they used were three revisions out of date. Mandatory quality control inspections of maintenance actions, as well as post-maintenance test flights prescribed in the General Operator's Manual and the manufacturer's maintenance manuals (that included the replacement of the flight control servo), were not performed. (This report was modified on June 16, 2009)