15.1 Aircraft indicating systems provide information to aircrew on the condition of aircraft systems and equipment, the aircraft’s flight status and other parameters necessary for safe aircraft operation, and/or to maintain adequate situational awareness. The Authority recognised Airworthiness Codes defined in Section 1 of this manual prescribe requirements for aircraft indicating systems. However, Defence aircraft can utilise indicating systems, such as helmet mounted displays, that are not used in civil aircraft and represent relatively recent advancements in military aircraft technology. Consequently, the civil and military Airworthiness Codes may not prescribe requirements for these systems. Therefore, the Authority prescribes airworthiness design requirements for indicating systems, to supplement the civil and military Airworthiness Codes.
15.2 This Chapter presents Authority prescribed airworthiness design requirements for Defence aircraft indicating systems.
15.3 Defence aircraft indicating systems must conform to standards appropriate to the functions that the instrument or display will perform. Authority recognised civil and military Airworthiness Codes prescribe design requirements that provide a sound foundation for the safe design of common Defence aircraft indicating systems (including those used as a Primary Flight Reference (PFR)). However, indicating systems that are in the early stages of technology development may be proposed for fitment to Defence aircraft to satisfy a capability need and design requirements for such systems may not have been prescribed in Authority recognised Airworthiness Codes. Consequently, applicants for an Australian MTC or MSTC must propose, for Authority approval, airworthiness design requirements based on the intended function and operation of the indicating system.
15.4 Design Requirement (Essential). Where a novel indicating system for which design requirements are not prescribed in Authority recognised Airworthiness Codes is intended for use in a Defence aircraft, airworthiness design requirements for the indicating system must be identified, and proposed for Authority approval.
15.5 Indicating systems are used for a wide variety of purposes ranging from those having no safety implications to those directly affecting safe flight. The proposed use of novel indicating systems must be clearly understood in order to define suitable design requirements. For example, novel indicating systems may be used to display information to the crew that:
enhances situational awareness or represents mission system status or performance, where the loss or presentation of misleading information does not impact safe flight;
could pose a hazard to safe flight if misleading information was presented to the crew; or
represents PFR information.
15.6 For those displays providing mission system status/performance or situational awareness information that does not impact safe flight if the information is lost or is misleading, failure of the equipment/system must not adversely impact other display system functions that present information necessary for safe flight. In these circumstances, the indicating system design requirements need only confirm that the system does not adversely affect other aircraft systems necessary for safe flight.
15.7 Where the presentation of misleading information may pose a hazard to safe flight in a novel display system (eg display of weapons system radar data on a HUD for weather avoidance), an additional level of data assurance is required, commensurate with the impact of the misleading data on safe operations. In these circumstances, the application of design requirements from the Authority recognised Codes for display systems having similar characteristics may be a suitable starting point, but is likely to require supplementation to account for the system’s novel features or approach to displaying information.
15.8 The presentation of reliable and accurate PFR information is particularly important due to the data’s criticality to safe aircraft operations. Such applications may not be adequately catered for by ‘standard’ indicating system design requirements prescribed in Authority recognised Codes, and additional design requirements are often necessary to provide the required level of design assurance for these systems. For example, helmet mounted displays (HMD) may provide both flight reference and mission systems information overlayed on the pilot’s field of view. Where a HMD is required to function as a PFR, it must satisfy the applicable design requirements prescribed in civil and military Airworthiness Codes as a minimum. However, some unique features of HMD may pose hazards associated with the human machine interface that are not relevant to other types of displays (eg visibility of key flight data at all times may be problematic during head movement). These characteristics may not be adequately accounted for in Authority recognised Airworthiness Codes.
15.9 Where a novel application of an existing indicating system is proposed, airworthiness design requirements must be identified and proposed to the Authority for approval.
15.10 Further guidance on implementing the indicating systems design requirements prescribed in this chapter can be provided by the chapter sponsor.