9.1 During military aircraft operations, avionics and other aircraft equipment is often exposed to extreme environmental conditions. This equipment must continue to function adequately when exposed to these environmental extremes and, therefore, must satisfy the requirements of an appropriate environmental standard.
9.2 While aircraft equipment will normally be designed to comply with either a civil or military environmental standard, the environmental conditions defined within the standard may not reflect those in which the Defence aircraft will operate. Further, civil Airworthiness Codes may not require equipment qualification for operations in the often much harsher environments experienced during military operations. Consequently, the Authority prescribes airworthiness design requirements for environmental qualification of aircraft equipment to supplement the Airworthiness Codes and provide a basis for verifying the acceptability of aircraft equipment for safe operation or to satisfy capability requirements for Defence aircraft.
9.3 This Chapter prescribes Authority supplementation to the aircraft equipment environmental qualification requirements in recognised civil and military Airworthiness Codes. Importantly, the airworthiness design requirements in this chapter are not suitable for application in isolation from an Airworthiness Code. The Authority's requirements for the application of recognised Airworthiness Codes are defined in Section 1 of this manual.
9.4 This section presents the Authority prescribed environmental qualification design requirements, applicable to Defence aircraft, that support safe operation of aircraft equipment when exposed to the expected environmental conditions.
9.5 Design Requirement (Essential). An applicant for an airworthiness instrument must identify, and propose to the Authority for approval, any supplementation to the aircraft's Primary Certification Code necessary to account for the identified environmental conditions.
9.6 While the majority of Defence aircraft will operate in environmental conditions that are appropriately covered by the requirements prescribed in Authority recognised Airworthiness Codes, some Defence aircraft are required to operate in environments that were not considered by the original designers. Further, qualification testing may identify shortfalls against the requirements of the standard that, while acceptable to the original certifying authority, may not be appropriate for Defence operations. In these cases, the delta between the ‘certified’ environmental conditions and those in which the aircraft is required to operate, must be established and any associated hazards analysed to determine whether the shortfall(s) poses a risk to safe flight and whether supplementation of the Code is therefore required.
9.7 Since Defence airworthiness design requirements establish the basis for safe aircraft operations, they are not usually applied to mission systems whose functions are not required for safe flight. However, environmental qualification is equally applicable to mission systems. After all, verifying that aircraft equipment can safely operate in the identified environmental conditions would be meaningless, without confirmation that the aircraft mission systems can adequately perform their intended functions in those in-flight and on ground environmental conditions where mission systems functionality is required. The following design requirements are not prescribed by the Authority, but should be considered when establishing requirements for Defence aircraft equipment environmental qualification.
9.8 Capability design requirement. The in-flight and on ground environmental conditions in which Defence aircraft mission systems equipment is required to operate should be established.
9.9 Capability design requirement. Defence aircraft mission systems equipment should be capable of operating in the identified environmental conditions where mission systems functionality is required.
9.10 The aircraft Type Certification Basis will define the environmental conditions under which aircraft equipment that provides safety related functions is required to operate in flight. These conditions can be used as the basis for establishing the environmental conditions that missions systems may be subjected to and therefore identify, on the basis of the potential impact on capability, whether mission equipment should be able to withstand the same in-flight conditions.
9.11 In addition to establishing the in-flight environmental conditions, Defence aircraft systems may be required to operate for extended periods in ground environmental conditions that may not be suitably catered for in the extant civil and military environmental standards. For example, aircraft systems may need to be operated on the ground to support:
flight crew, mission crew and technician training;
preparation and preservation of aircraft in a state of readiness to support contingency operations; and
fault finding or other maintenance activities.
9.12 The worst-case environmental conditions and time that mission systems and equipment may be required to operate on the ground should be established, and the ability of Defence aircraft equipment to function adequately under these conditions should be evaluated. The results of this evaluation may be used to support decisions on further testing/qualification of aircraft equipment and/or supplemental environmental conditioning on the ground or aircraft environmental control systems enhancements.
9.13 Note that the ground environmental categories defined in DEF (AUST) 5168 Issue 2, The Climatic and Environmental Conditions Affecting the Design of Military Materiel may define Australian unique environments that are not encapsulated in the common civil and military environmental standards. Where relevant, these ground environmental conditions should also be considered when establishing the worst-case environments for Defence aircraft operations.
9.14 Further guidance on implementing the equipment environmental qualification requirements prescribed in this chapter can be provided by the chapter sponsor.