1.1 Joint Directive 21/2021 requires the Defence Aviation Safety Authority (hereinafter referred to as the Authority) to establish a Defence Aviation Safety Program which, inter alia, includes ‘establishing and certifying the initial safety requirements and standards for Defence … aviation platforms/systems’. Inherent in this responsibility is the requirement for the Authority to prescribe minimum requirements for the design of Defence aircraft, engines, propellers and other aircraft-related equipment. The Defence Aviation Safety Program Manual Volume 1 requires the Authority to ‘issue standards, inclusive of airworthiness codes, as required for the implementation of the DASR’. The Authority’s repository for these ‘standards and airworthiness codes’ with respect to aircraft design for Defence aviation platforms and systems, also known as airworthiness design requirements, is the Defence Aviation Safety Design Requirements Manual (DASDRM).
1.2 This chapter of the DASDRM:
describes the purpose and scope of the manual,
explains the approach adopted by the Authority for prescribing airworthiness design requirements, and
describes the structure of the manual.
1.3 The DASDRM prescribes design requirements for aircraft systems and functions that are necessary to achieve safe flight in Defence’s proposed configuration, role and operating environment. It also prescribes additional design requirements that may further improve the level of safety, and that should be implemented where reasonably practicable. In each case, the DASDRM identifies the hazard(s) that the design requirement is intended to treat, to provide a basis for informed risk management where an aircraft design fails to meet the design requirement. Airworthiness requirements for crewed aircraft are presented in Sections 2 and 3 of this manual, while Uncrewed Aircraft Systems (UAS) are covered in Section 4.
1.4 The Australian Work Health and Safety Act and the Work Health and Safety Regulations (collectively, WHS Legislation) apply to Defence aviation. Defence aircraft must therefore present a safe work environment for aircrew and passengers, and the airworthiness design requirements in this manual make a substantial contribution to this aim. By its nature, however, the concept of ‘airworthiness’ has a primary focus on safe flight. Consequently, airworthiness design requirements require supplementation if Defence is to fully meet its WHS Legislation obligations. Section 1, Chapter 2 of this manual expands on this important concept.
1.5 Similarly, capability and interoperability is not a specific consideration when establishing that an aircraft is capable of safe flight. However, robust design for capability and interoperability contributes to mission success, and therefore the safety of aircrew. Consequently, while capability and interoperability design requirements are not a primary focus of the DASDRM, design requirements that support capability and interoperability outcomes are included where appropriate. Section 1, Chapter 4 describes how capability and interoperability design requirements are incorporated into the DASDRM.
1.6 Finally, while the DASDRM focuses primarily on aircraft, it recognises that some off-aircraft systems (eg Mission Planning Systems, Health and Usage Monitoring Systems and aerodrome installations) can have a direct and substantial impact on safe flight. While these ground based systems clearly are not within the scope of airworthiness, they are relevant to the broader context of aviation safety and the Authority may therefore elect to prescribe relevant design requirements. These requirements are presented in Section 5 of the DASDRM for aviation support systems and Section 6 for aerodromes.
1.7 This chapter, and the remainder of the DASDRM, refers to both ‘design requirements’ and ‘design standards’, which may appear to the reader to be interchangeable. This is often, but not always, the case. The latter specifically refers to a standard published by a civilian or military standards body, for example a US MIL STD or an RTCA standard. Airworthiness design requirements, on the other hand, define the safety outcome being pursued. This can be achieved via a worded requirement (eg “PVC wiring must not be used in Defence aircraft”) or via reference to a design standard.
1.8 The Authority employs three foundational principles when prescribing airworthiness design requirements for Defence aircraft:
the Authority recognises the airworthiness design requirements prescribed by several civil and military National/Military Airworthiness Authorities (NAAs/MAAs) as providing a sound foundation for the safe design of Defence aircraft;
the Authority may prescribe supplementation to these airworthiness design requirements, where an aspect of a requirement is judged deficient or to support application to Defence’s unique role and operating environment; and
the Authority requires the conduct of a System Safety Program, to provide a robust means for identifying and analysing aircraft hazards during the design process, and for eliminating or minimising the resultant risks so far as is reasonably practicable.
1.9 These three foundational principles are examined in the following sections.
1.10 Many NAAs/MAAs prescribe airworthiness design requirements for achieving safe flight through aircraft design (DASR 21 refers to these airworthiness design requirements as ‘Airworthiness Codes’). An Airworthiness Code is a complete and consistent set of airworthiness design requirements that define those attributes of aircraft systems or equipment that underpin safe flight. Airworthiness design requirements are usually prescribed by civil NAAs based on aircraft types. For example, both the USA Federal Aviation Administration (FAA) and the European Aviation Safety Agency (EASA) prescribe separate suites of airworthiness design requirements for light and heavy fixed wing aircraft, and light and heavy rotorcraft.
1.11 The development and maintenance of an Airworthiness Code is a substantial undertaking. Rather than define a Defence-unique Airworthiness Code, the Authority has elected to recognise the suite(s) of airworthiness design requirements (ie Airworthiness Codes) prescribed by several other NAAs and MAAs that have been demonstrated through extensive operating history to achieve safe flight, and then prescribe supplementation as required. The Authority recognised ‘Airworthiness Codes’ are described in Section 1 Chapter 3 of this manual.
1.12 The Authority recognised Airworthiness Codes will inevitably require supplementation to account for:
Defence’s unique Configuration, Role and/or operating Environment (CRE);
deficiencies in the level of safety provided by the airworthiness design requirements prescribed in the Code, detected by the Authority through local research or experience (eg investigations into aircraft incidents); or
intentional ambiguities within the airworthiness design requirements, where it is assumed that tailoring will be required to meet the needs of the specific application.
1.13 Not all elements of aircraft design covered in Authority recognised Airworthiness Codes will require supplementation. Where supplementation or tailoring of an Airworthiness Code is required, the airworthiness design requirements prescribed by the Authority are contained in this manual. The expectation is that these airworthiness design requirements will be applied in a practical and pragmatic manner. To support their pragmatic implementation, the Authority has classified each airworthiness design requirement as either ‘Essential’ or ‘Recommended’.
1.14 Essential and Recommended airworthiness design requirements. The Authority classifies each airworthiness design requirement as either Essential or Recommended, using the following criteria:
Essential - an Essential airworthiness design requirement is one where non-compliance would result in a marked reduction in the level of safety afforded by the design. Essential design requirements may also be defined to satisfy legislation, and Defence policy and/or operational regulation requirements.
Recommended - a Recommended airworthiness design requirement represents emerging aviation industry ‘good practice’ that is not yet widely accepted/implemented, or presents an opportunity to increase the level of safety afforded by the design (usually above that provided in Airworthiness Codes).
1.15 While Essential airworthiness design requirements define the level of safety that must be achieved by a design, they are not immutable. The Authority, in consultation with the relevant capability manager where applicable, may approve an alternative airworthiness design requirement in the following circumstances:
where analysis confirms the alternative design requirement achieves an equivalent level of safety;
where analysis shows the alternative design requirement, supplemented by operational risk treatments, should achieve an equivalent level of safety; or
where enforcing the Essential design requirement would have a marked negative effect on capability or cost, and an alternative (but less safe) design requirement is in Defence’s best interests.
1.16 On occasion the Authority may, in consultation with the capability manager, agree to an alternative design standard that does not satisfy the Authority agreed safety criteria, where meeting the prescribed standard would have a pronounced impact on Defence capability and is not in Defence’s best interest. In these circumstances, a tailored design standard could be agreed to contextualise the level of safety afforded by the design for the military role and operating environment of the aircraft. Any proposed tailoring of design standards by an applicant for type certification and/or design approval from the Authority, which results in changes to agreed safety criteria, must be supported by documented rationale that includes:
the capability manager’s confirmation that a clear (well-defined) and documented capability imperative for the proposed tailoring exists;
the applicant’s confirmation that compliance with the prescribed standard impedes that capability imperative;
the applicant’s characterisation of the delta between the prescribed standard and the tailored standard;
the applicant’s, with the assistance of the capability manager (or delegate), characterisation of the risk due to this delta; and
the capability manager’s (or delegate’s) formal conclusion that the tailored safety criteria presents a credible and defensible level of safety for that Defence aircraft, contextualised for ADF operations.
1.17 Once the preceding outcomes have been confirmed, a Military Certification Review Item (MCRI) will be raised by the applicant to reflect the agreed tailoring including any essential risk controls to achieve the defined level of safety.
1.18 Given the nature of Recommended design requirements, their adoption is not mandated by the Authority. Nevertheless, the recommended requirements may assist duty holders to satisfy obligations under WHS legislation for eliminating or minimising risk SFARP. Consequently, the ‘designer’, in conjunction with the ‘sponsor’11 as a shared duty holder, should determine if adoption of a recommended requirement is reasonably practicable by assessing the improvement in the level of safety afforded by the recommended design requirement against the likely cost(s) of implementation.
1.19 Compliance with design standards is the principal means by which safe design of an aircraft is achieved. However, in isolation, a standards-based approach may not provide a complete basis for Type Certification of an aircraft. After all, many standards are inherently stove-piped, and therefore further analytical effort is required to identify and control system-level hazards. Further, standards are often written with ‘vanilla’ applications in mind; novel aircraft design features are likely to pose novel hazards, which are not catered for within the standard.
1.20 System Safety is an engineering discipline that embraces safety as a core aspect of any given system design (or design change). System safety programs employ a suite of engineering tools and techniques to identify and analyse aircraft hazards during the design process, and provide a management framework to evaluate and control the resultant risks. When applied well, a system safety program is an essential adjunct to a standards-based design approach.
1.21 Formal system safety programs are required for all Defence aircraft acquisitions and Major changes to a type design. The Authority’s requirements for System Safety programs are presented in Section 2 Chapter 2 of this manual.
1.22 This manual comprises the following six sections:
Section 1 – Application of Airworthiness Design Requirements. This section defines the purpose and scope of the DASDRM and defines the Airworthiness Codes that have been recognised by the Authority as providing a sound foundation for the design of Defence aircraft. It also describes the extent to which airworthiness design requirements contribute to Defence meeting its WHS Legislation obligations. Finally, Section 1 describes the application of capability and interoperability standards to aircraft designs.
Section 2 – Integrated Design Requirements. This section prescribes airworthiness design requirements for those engineering disciplines that pervade most aspects of aircraft systems design or affect multiple systems such as system safety, electromagnetic environmental effects and crash protection.
Section 3 – Aircraft System Design Requirements. This section prescribes airworthiness design requirements for aircraft systems such as communications, navigation, structures (fixed and rotary wing) and propulsion. The only systems included in this section are those where the Authority recognised Airworthiness Codes do not provide satisfactory coverage for Defence aircraft designs.
Section 4 – Uncrewed Aircraft Design Requirements. This section prescribes airworthiness design requirements for UAS.
Section 5 – Aircraft Support Systems. This section prescribes design requirements for aircraft support systems and ground based equipment, where the systems/equipment have a direct and substantial effect on safe flight, such as aeronautical life support equipment and mission planning systems.
Section 6 – Aerodrome Design Requirements. This section prescribes airworthiness design requirements for Defence aerodromes and heliports.
1.23 Each chapter in this manual is sponsored by a relevant DASA directorate, a Delegate of the Safety Authority (DoSA) or a suitable subject matter expert. Annex A lists these sponsors, who are the first point of contact for requests for interpretation or suggestions for improvement.