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Findings and Safety Action

Summary

FINDINGS

The investigation identified the following contributing safety factors.

  • The part number A44700-009 roll spoiler actuator, as fitted to TNG, was susceptible to fatigue cracking as a result of deficiencies within the design of the actuator cylinder base
  • The actuator ruptured as a result of fatigue cracking initiated due to the design deficiency and the accumulation of a sufficient number of flight cycles
  • Rupture of the actuator allowed the loss of fluid contents from the number-2 hydraulic system, and the subsequent failure of that system.

SAFETY ACTION

Aircraft manufacturer

On 18 August 2004, the manufacturer issued In-Service Activity Report (ISAR) 2004-07-2760 advising that it considered the overall risks associated with the failure of the actuator as low, and to raise operator awareness of the actuator failure mechanism.

Transport Canada

Transport Canada, being the certification authority for the Dash 8 series of aircraft, conducted its own investigation of the issues associated with actuator failure. In communication with the ATSB, Transport Canada concurred with the aircraft manufacturer's risk management position and agreed that on the basis of current failure rates, no additional action was warranted.

Australian Transport Safety Bureau

The ATSB reviewed the responses and positions of the aircraft manufacturer, Transport Canada and the aircraft operator in relation to the potential for roll spoiler actuator failure to affect operational safety of the Dash 8. While it supports the risk management approach adopted by the manufacturer and Transport Canada, the ATSB believes that the issue of landing performance limitations imposed by a hydraulic system failure is not adequately addressed by this approach. Therefore, the ATSB issues the following safety advisory notice.

Safety Advisory Notice SAN20050012

The Australian Transport Safety Bureau notifies operators of Dash 8 aircraft fitted with part number A44700-007 and/or A44700-009 roll spoiler actuator components, of the increased risk of the cracking and/or rupture failure of the actuator cylinder section as the actuators accumulate service cycles. Failures have been sustained by actuators with service lives ranging from 27,909 to 41,716 cycles. Cracking or rupture of an actuator cylinder results in the loss of contents and subsequent failure of the associated aircraft hydraulic system. Given that the loss of an aircraft hydraulic system will result in extended landing distance requirements, operators are advised to consider the safety implications of operating affected aircraft to regions where the increased landing distance requirements may not be easily accommodated by available primary or alternate aerodromes.

 
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