9.1 The Environmental Control System (ECS) provides temperature, humidity, ventilation and pressure control to passenger/cargo areas, aircraft systems and equipment. The system must be able to provide this control under any possible role, configuration and environment in which the platform will operate. ECS air may be derived from internal sources (engine or auxiliary power unit), external sources (ram air or air-conditioning cart) or an ECS dedicated compressor. Heat generated by aircraft equipment and occupants is usually dispersed external to the aircraft and needs to be controlled to meet safety and mission requirements. ECS functions and sub-systems may include, but are not limited to: pressurisation, heating, cooling, ventilation, moisture control, pressure and anti-G suit control, defogging, defrosting, anti-icing, rain removal, windshield washing, and electronic and electrical thermal management.
9.2 While compliance with the Authority recognised civil and military Airworthiness Codes described in Section 1 of this manual usually satisfies aircraft ECS safety objectives, the Codes may not account for ECS loads associated with military loads and mission systems. Further, Defence experience with ECS has identified that simple application of the Codes may not adequately account for the Australian operating environment, particularly where ground operations in harsh environmental conditions are expected. Consequently, the Authority prescribes airworthiness design requirements for Defence aircraft ECS to supplement these Airworthiness Codes and support the provision of adequate ECS capability for Defence aircraft operations.
9.3 This Chapter presents the Authority prescribed airworthiness design requirements for Defence aircraft ECS. 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 Design Requirement (Essential). Defence aircraft electronic equipment cooling capacity must be evaluated and verified to provide sufficient cooling for safety of flight systems, for both initial aircraft designs and design changes, or additional ECS capacity must be provided.
9.5 The safety of aircraft designs may be compromised if the ECS is not capable of providing adequate cooling to electrical or electronic equipment. Additionally, changes to ECS ducting or flow paths may impact ECS cooling performance even though capacity remains the same. As part of initial aircraft design certification activities, or during design changes that either add thermal loads to existing ECS demands or change the ECS characteristics, the ECS capacity and performance must be evaluated to verify that it remains adequate for the required load conditions.
9.6 Design Requirement (Essential). Where applicable, Defence aircraft environmental control systems must satisfy the requirements for anti-G suit systems prescribed in MIL-E-18927E(AS), Environmental Control Systems, Aircraft, General Requirements for.
9.7 Authority recognised civil Airworthiness Codes do not prescribe requirements for anti-G suit supply systems. To support safe anti-G suit operation where a Defence aircraft is to be used in operations requiring anti-G protection, compliance with an appropriate military standard is required.
9.8 Design Requirement (Recommended). Environmental control systems should be capable of maintaining the required temperature, pressure, humidity and ventilation control in the ground environmental conditions for the worst-case duration applicable to the Defence aircraft CRE, described in:
MIL-HDBK-310, Global Climatic Data for Developing Military Products
DEF(AUST) 5168, The Climatic and Environmental Conditions Affecting the Design of Military Materiel.
9.9 Compliance with Authority recognised Airworthiness Codes usually satisfies design safety objectives for the purposes of maintaining occupant and aircraft safety during flight (eg pressure and temperature control of occupied spaces and thermal control of aircraft equipment). However, Defence experience in the past, particularly for aircraft that are based on a modified civil variant, has identified that compliance with these Codes may result in an ECS that does not satisfy either occupant or equipment environmental control needs when the aircraft is on the ground. Therefore, the applicable environmental conditions for ground operations should be defined and the ECS evaluated to verify that it can support the associated environmental control requirements, or to identify supplementary ECS capability (eg ground air conditioning systems) if required.
9.10 Design Requirement (Recommended). Cooling for electronic equipment provided by Defence aircraft environmental control systems should allow for 50% greater load capacity than that required for the originally certified aircraft design.
9.11 Military aircraft operational experience demonstrates that 50% growth capacity from the originally certified design is likely to be sufficient to accommodate future changes in avionics, especially on fighter, bomber and electronically intensive platforms. Additional ECS capacity may be provided through: ECS designs having an electronic heat dissipation load greater than the equipment heat load of the originally certified design; aircraft designs that permit fitment of a larger capacity ECS system; or a combination of these approaches.
9.12 While not essential for the achievement of a safe aircraft design from an ECS perspective, Defence experience has demonstrated that formal ECS management and planning supports the achievement of an appropriate level of ECS capacity and performance. Consequently, the Authority recommends the use of the following two ECS planning documents:
ECS Operating Modes Document (ECSOMD), and
ECS Analysis and Integration Plan (ECSAIP).
9.13 ECS air for Defence aircraft is a resource and, therefore, should be managed in a similar manner to other platform resources such as electrical loads and weight and balance. Critical modes of operation will be present in Defence aircraft ECS, in which the demands on ECS resources may be elevated or where normal ECS resources may be unavailable. These critical modes of operation should be identified during initial aircraft design to establish the required ECS capability, to limit the potential for ECS resources to be compromised throughout the Defence aircraft’s service life, and to provide a basis for evaluating the impact of design changes on Defence aircraft ECS.
9.14 One approach to documenting the identification and analysis of ECS modes is an ECS Operating Modes Document (ECSOMD). An ECSOMD should be raised for each defence aircraft acquisition. The SPO responsible for managing the Defence aircraft, should maintain the ECSOMD throughout the aircraft’s service life, and update the document for each modification that has an impact on available ECS resources.
9.15 Additional oversight of ECS resources during design changes may be required if the ECS:
has an uncertain or undefined spare and/or utilised capacity,
may impose limitations on aircraft operations, or
will be nearing capacity in the immediate future through concurrent or future defined design changes.
9.16 One method of applying this additional oversight is through the use an ECS Analysis and Integration Plan (ECSAIP). An ECSAIP should be developed for all design changes having the potential to significantly impact ECS capabilities. The ECSAIP should build on the ECSOMD, demonstrate that ECS requirements have been adequately identified, and provide a vehicle for ongoing ECS management through the aircraft life of type.
9.17 For additional information relating to ECS integration issues, refer to Section 2 Chapter 9, Equipment Environmental Qualification.
9.18 Further guidance on implementing the ECS design requirements prescribed in this chapter can be provided by the chapter sponsor.