AD/AS 355/32 - Servo Control Securing Screws

Overview

The Civil Aviation Regulations 1998, as amended through legislative instrument F2006B02486, introduced specific Airworthiness Directives to address issues with Eurocopter AS 355 (Twin Ecureuil) Series Helicopters. This legislation was enacted by the Commonwealth of Australia to ensure the safety and reliability of civil aviation operations. The identified problem was the potential failure of servo control securing screws due to hydrogen embrittlement, which was discovered following an investigation into main rotor vibrations in AS350 helicopters. This directive requires operators of AS355 helicopters to inspect, replace, and quarantine screws as specified to prevent further incidents. The policy objective behind this directive is to enhance the safety of air travel by proactively addressing mechanical failures that could lead to catastrophic outcomes.

Scope and Application

The Civil Aviation Regulations 1998, specifically Part 39 - 105 under the Civil Aviation Safety Authority's Schedule of Airworthiness Directives, applies to all AS355 helicopters equipped with Dunlop servo control assemblies. The directive AD/AS 355/32 mandates several critical checks and modifications to the servo control securing screws to ensure airworthiness and safety. This requirement is aimed at addressing issues related to hydrogen embrittlement which has caused screws to fail, potentially leading to significant safety hazards. The directive is applicable nationwide and must be adhered to by all operators of the specified helicopter models. Compliance involves rigorous checks and modifications, such as removing and inspecting set screws, replacing failed screws, and reporting any incidents to the nearest airworthiness office within specified timeframes. Subordinate instruments may further detail the procedures and standards to be met, but the primary requirement remains clear and unambiguous in ensuring the safety of the aircraft and its operations.

Key Provisions

The Civil Aviation Regulations 1998, under Part 39, contains specific provisions for the airworthiness of Eurocopter AS 355 (Twin Ecureuil) Series Helicopters, as outlined in AD/AS 355/32. Section 105 of this legislation mandates a series of requirements aimed at ensuring the safety of these helicopters. Firstly, Section A requires the removal of all 5mm diameter set screws P/N BS 4168 that attach the servo block to the body of the actuator, one at a time. Before refitting these screws, their strength must be checked using a threaded test block or nut and appropriate spacer, applying a torque of 4.5Nm (40 in lbs) to ensure they meet the required load specifications. Secondly, Section B instructs the removal from service of all servo block attaching screws marked "HK 129". Section C mandates a thorough torque check of all 5mm screws attaching both end fittings, while Section D stipulates that if any screw is found to be failed, all screws fitted to that end fitting or servo block must be replaced. Lastly, Section E requires that all screws that are not refitted be quarantined and reported to the nearest airworthiness office by telephone. The Act imposes several obligations on the parties it governs. Firstly, operators of AS355 helicopters fitted with Dunlop servo control assemblies must ensure that the checks and replacements of the servo control securing screws are completed within specific timeframes. For example, Section A requires these checks to be conducted within 10 hours of Continuous Time in Service (CTIS) after 12 May 1988. Section B necessitates that the removal of the marked screws must be completed within 25 hours CTIS after inspection, while Section C requires the torque check to be done within 25 hours CTIS after 12 May 1988. Section D mandates that the replacement of any failed screws must occur before further flight, and Section E requires that quarantined screws be reported within 48 hours of their discovery. Failure to comply with the provisions outlined in the Civil Aviation Regulations 1998 can result in various consequences. While the specific penalties for non-compliance are not detailed in the legislative instrument, it is likely that breaches could lead to civil or criminal penalties under broader aviation safety regulations. For instance, non-compliance could result in the grounding of the aircraft until the required checks and repairs are performed, potentially leading to significant operational disruptions and financial losses for the operator. Additionally, persistent non-compliance could lead to more severe penalties, including fines or legal action, as enforced by the Civil Aviation Safety Authority.