AD/DHC-6/51 Amdt 4 - Engine Nacelle Lower Longerons

Overview

The Civil Aviation Regulations 1998, enacted by the Australian Government, aim to ensure the safety of civil aviation. These regulations, administered by the Civil Aviation Safety Authority (CASA), include specific directives to address identified safety issues. One such directive, AD/DHC-6/51 Amendment 4, pertains to the DHC-6 (Twin Otter) series aeroplanes, addressing the problem of buckles and cracks in engine nacelle lower longerons. This directive mandates inspections and replacement of failed longerons to maintain airworthiness. The policy objective is to enhance safety by adhering to service bulletins and ensuring timely inspections based on the type of tyres, skis, or floats installed, and the history of modifications applied to the aircraft. This legislative instrument aims to provide clear and precise guidelines for maintaining the structural integrity of the engine nacelle lower longerons, thereby preventing potential failures that could compromise flight safety. By referencing Transport Canada’s directives and amendments, it ensures alignment with international safety standards. The directive was introduced to provide a structured approach to inspections and maintenance, tailored to different configurations and operational histories of the aircraft. The enforcement of these regulations by CASA ensures compliance and upholds the safety standards required in Australian civil aviation.

Scope and Application

The Civil Aviation Regulations 1998, Part 39 - 105, governs the airworthiness directives for DHC-6 (Twin Otter) series aeroplanes, specifically addressing the maintenance and inspection requirements of engine nacelle lower longerons. The regulations apply to all DHC-6 series aircraft and mandate compliance with de Havilland Inc. Service Bulletin 6/509, which requires the replacement of any buckled or cracked lower longerons with serviceable parts. The regulations specify different inspection intervals based on the type of tyres or landing gear installed, with more frequent inspections required for aircraft fitted with high or intermediate flotation tyres, or skis and floats, especially if operating from unprepared surfaces or very rough water. The inspection intervals vary from 50 hours to 400 hours, depending on the specific configuration of the aircraft, and must also occur after each hard landing. This legislation ensures that all DHC-6 series aeroplanes meet necessary safety standards, with specific thresholds and intervals determined by the equipment and operational environment of the aircraft.

Key Provisions

The Civil Aviation Regulations 1998, specifically Part 39, Section 105, includes a schedule of airworthiness directives pertinent to DHC-6 (Twin Otter) series aeroplanes. The relevant section in this context is AD/DHC-6/51 Amendment 4, which pertains to the engine nacelle lower longerons. This directive mandates inspections and, if necessary, the replacement of these components according to de Havilland Inc. Service Bulletin 6/509 (Section 1). The requirement is that if buckles or cracks are discovered in the engine nacelle lower longerons, they must be replaced with serviceable parts. This directive applies to the DHC-6 series aeroplanes and references Transport Canada AD CF-81-07R4 (Note 1). It is important to note that even if Modification 6/1655 has been previously accomplished, it does not exempt the aircraft from the inspection requirements of this directive (Note 2). The obligations imposed by this directive include regular inspections of the engine nacelle lower longerons, with specific intervals depending on the type of tyres or landing gear installed on the aircraft. For aircraft fitted with high flotation tyres or intermediate flotation tyres not installed in accordance with de Havilland Standard Option Only (SOO) 6048, without Modification 6/1655, inspections must occur within 50 hours after 6 March 1992 and subsequently at intervals not exceeding 50 hours. The same requirement applies to aircraft equipped with skis or floats without Modification 6/1655. For aircraft with intermediate flotation tyres installed in accordance with de Havilland SOO 6048, without Modification 6/1655, or with skis or floats but equipped with Modification 6/1655, inspections should occur within 50 hours after 6 March 1992 and at intervals not exceeding 200 hours. For all other aircraft, inspections must occur within 400 hours after 6 March 1992 and at intervals not exceeding 400 hours. In all cases, inspections are also required after each hard landing. Failure to comply with the airworthiness directive and the mandated inspection intervals could result in the aircraft not meeting the required airworthiness standards, potentially leading to operational restrictions or grounding of the aircraft by the Civil Aviation Safety Authority (CASA). Although the specific penalties for non-compliance are not detailed within this section, non-compliance with CASA directives generally can lead to enforcement actions, fines, or other regulatory penalties as prescribed by the Civil Aviation Act 1988. The exact penalties would depend on the nature and severity of the non-compliance, but they could include significant financial penalties and potential criminal charges for those responsible for the oversight of the aircraft's maintenance.