4.1 The interaction of electrical and magnetic fields emanating from systems within an aircraft, or the interaction between the aircraft and the external environment, can create unwanted effects, which may adversely impact the safe flight of Defence aircraft. Protection of Defence aircraft designs against Electromagnetic Environmental Effects (E3) therefore must be established as part of initial design, subsequent modification, ongoing maintenance, and any time an aircraft or system experiences a change in its Configuration, Role or operating Environment (CRE).
4.2 Authority recognised Airworthiness Codes prescribed by National and Military Airworthiness Authorities (NAAs and MAAs) include airworthiness design requirements for E3, together with extensive guidance in most instances. However, the NAA/MAA prescribed design requirements require tailoring to:
account for the unique CRE of Defence aircraft;
ensure that the requirements are applied in a pragmatic manner, particularly for non-safety related systems and equipment; and
ensure that radiation hazards posed by aircraft emitters comply with relevant Australian legislation and Defence policy requirements.
4.3 This Chapter presents the Authority prescribed airworthiness design requirements for Defence aircraft E3. The Chapter also presents design requirements to establish E3 protection of mission systems.
4.4 The application of E3 design requirements prescribed by NAAs and MAAs is not straightforward. While many of the E3 requirements prescribed by NAAs and MAAs ensure that E3 will not impact safe flight, the approaches adopted often differ and may not adequately account for Defence’s CRE. To account for these differences in E3 protection approaches, this Chapter presents design requirements utilising the following elements of E3 described in MIL-STD-464C Electromagnetic Environmental Effects Requirements for Systems as the basis, with tailoring to satisfy Defence’s CRE where required:
Margins
Intra-system Electromagnetic Compatibility (EMC)
Subsystems and equipment Electromagnetic Interference (EMI)
Electrostatic charge control
External Radio Frequency (RF) Electromagnetic Environment (EME)
High-power microwave (HPM) sources and Electromagnetic Pulse (EMP)
Lightning
Electromagnetic radiation hazards
Electrical bonding
External grounds
Life cycle E3 hardness
Emanations Security (EMSEC)
System radiated emissions (Emissions Control (EMCON))
Electromagnetic spectrum supportability.
4.5 This chapter presents the Authority prescribed E3 airworthiness design requirements for Defence aircraft acquisitions and modifications, and E3 design requirements for supporting Defence aircraft capability. Finally, the Chapter provides guidance associated with E3 management and planning.
4.6 To ensure that adequate E3 protection is afforded for the Defence aircraft’s CRE, this section presents Authority prescribed E3 airworthiness design requirements applicable to Defence aircraft acquisitions.
4.7 Design Requirement (Essential). The application of margins during Defence aircraft E3 certification programs must satisfy the E3 airworthiness design requirements prescribed in an Authority recognised Airworthiness Code.
4.8 Design Requirement (Essential). A 16.5 dB margin (of the maximum no-fire stimulus (MNFS) threshold) must be applied to all electro-explosive devices that could impact safe operation of Defence aircraft.
4.9 Margins are applied during E3 certification of aircraft systems and equipment to ensure that the equipment will continue to function when exposed to the proposed external and intra-system EME. Margins allow for inherent differences in equipment build quality and installations, and variability in test methods and outcomes. Authority recognised Airworthiness Codes presented in Section 1 Chapter 3 ensure that adequate margins are applied during E3 certification programs. However, these Codes (particularly civil Codes) may not cover the application of margins to Electrically Initiated Devices (EIDs), which is fundamental to ensuring that EIDs do not pose a hazard to safe flight (or personnel safety) when exposed to the associated EME, or do not suffer functional loss due to such exposure.
4.10 Design Requirement (Essential). Intra-system EMC, subsystems and equipment EMI, and electrostatic charge control certification for Defence aircraft must satisfy the E3 airworthiness design requirements prescribed in an Authority recognised Airworthiness Code.
4.11 All Authority recognised Airworthiness Codes prescribe requirements for intra-system EMC, subsystems and equipment EMI, and electrostatic charge control. These requirements ensure that there should be no adverse impact to safe flight due to intra-system interference or electrostatic discharge.
4.12 Design Requirement (Essential). The EME in which a Defence aircraft will operate must be established, and the associated High Intensity Radiated Field (HIRF) environment certification levels must be applied to the design.
4.13 The ability of Defence aircraft to operate safely in the external EME must be ensured through appropriate design, testing and analysis. Authority recognised Airworthiness Codes define HIRF environments for ‘normal’ aircraft operations (fixed and rotary wing). However, the ‘normal’ HIRF environments in these Codes and associated E3 standards may not provide adequate levels of protection for Defence’s CRE. The adequacy of the certified EME must be confirmed through comprehensive evaluation of the actual EME the Defence aircraft is expected to operate within. Further, the civil Codes generally do not define a HIRF environment for shipboard operations, but may define requirements based on special conditions where the aircraft is intended to operate to/from ships. Consequently, where Defence civil-derivative aircraft are required to operate to/from or in the vicinity of RAN vessels, an understanding of the HIRF environment certification (and influence over any design considerations if possible) must be established to support compliance demonstration for the Defence CRE.
4.14 Design Requirement (Essential). Where a requirement exists for High Power Microwave (HPM) and Electromagnetic Pulse (EMP) protection for Defence aircraft, the design requirements for HPM and EMP prescribed in MIL-STD-464C must be met.
4.15 HPM emitters (such as microwave weapons and counter measures) or EMP (eg nuclear blast effects) may adversely affect safety of flight systems. Given the nature of these threats, civil Airworthiness Codes do not include protection against these hazards. Where a capability need exists for Defence aircraft to be protected against HPM and/or EMP effects, compliance with relevant MIL-STD-464C requirements must be demonstrated.
4.16 Design Requirement (Essential). Lightning strike certification for Defence aircraft must satisfy the E3 airworthiness design requirements prescribed in an Authority recognised Airworthiness Code.
4.17 Design Requirement (Essential). Ordnance fitted to Defence aircraft must satisfy the requirements prescribed in MIL-STD-464C to remain safe during and after experiencing a lightning strike.
4.18 Authority recognised Airworthiness Codes prescribe requirements for lightning effects that ensure safe flight for Defence aircraft following lighting strikes. However, the civil Codes and associated standards do not prescribe requirements for lightning protection of ordnance, which must be demonstrated through the application of the requirements prescribed in MIL-STD-464C.
4.19 Radio Frequency (RF) emissions from Defence aircraft may pose hazards to fuel, ordnance and personnel. Military Airworthiness Codes and supporting standards prescribe requirements for protection against Hazards of Electromagnetic Radiation to Fuel (HERF) and to Ordnance (HERO). Civil Airworthiness Codes do not consider HERO, and only consider HERF in an oblique manner. Finally, both civil and military Codes either do not explicitly cover Hazards of Electromagnetic Radiation to Personnel (HERP) or rely on radiation protection standards that do not satisfy Australian legislation.
4.20 Design Requirement (Essential). Explosive ordnance intended for use on Defence aircraft must be certified as safe for operation and integration onto the aircraft, in the applicable EME, in accordance with the requirements prescribed in DEOP 115.
4.21 HERO design requirements are prescribed by MAAs to ensure that ordnance is capable of withstanding specified EME and remain both safe and functional. Defence policy on HERO, published by EODIV in DEOP 115 Defence Electro-explosive Hazards Manual, details the approved Defence approach to classification and certification for safe storage, transportation, handling, maintenance and operation of ordnance. DEOP 115 refers to MIL-STD-464 to define the EME that Defence EO must be certified within. Normally, EODIV assesses each proposed item of EO for HERO and issues appropriate data to platform engineering organisations to support integration onto Defence aircraft. Note that ordnance safety also depends on compliance with all other elements of E3 protection described in this chapter. Consequently, in addition to DEOP 115 requirements, all other applicable Authority prescribed E3 design requirements must be met.
4.22 Design Requirement (Essential). Safe distances from fuel sources during fuelling operations, including during air-air refuelling, defined in accordance with the requirements of USAF TO 31Z 10-4 or NAVSEA OP 3565 Vol 1, must be established for RF emitters fitted to Defence aircraft.
4.23 Authority approved military Airworthiness Codes prescribe requirements to ensure that fuel will not be ignited by aircraft radiated EME. The Authority approved civil Codes are not as comprehensive. MIL-STD-464C prescribes these requirements via references to USAF TO 31Z-10-4 Electromagnetic Radiation Hazards and NAVSEA OP 3565 (Vol 1) Electromagnetic Radiation Hazards to Personnel, Fuel and Other Flammable Material. In particular, identification and treatment of hazards associated with RF emitters during refuelling operations (including air-air refuelling where relevant) is essential. Note that fuel safety also depends on compliance with all other elements of E3 protection described in this chapter. Consequently, in addition to defining appropriate safe distances, all other applicable Authority prescribed E3 design requirements must be met.
4.24 Design Requirement (Essential). Aircraft occupants must not be exposed to RF levels that exceed the thresholds defined in the Defence Radiation Safety Manual.
4.25 Radio frequency emissions from Defence aircraft may pose hazards to personnel. Designers must ensure that Defence aircraft systems and equipment do not expose occupants to RF levels that exceed the specifications on Radiation Hazards contained in the Defence Radiation Safety Manual. Designers must also analyse emissions from Defence aircraft systems and establish appropriate safe distances to ensure that persons outside the aircraft are not exposed to RF levels that exceed the specifications on Radiation Hazards contained in the Defence Radiation Safety Manual.
4.26 Design Requirement (Essential). Defence aircraft systems, subsystems and equipment must be electrically bonded to satisfy the requirements of an Authority recognised Airworthiness Code.
4.27 Design Requirement (Recommended). Metal interfaces in Defence aircraft systems, subsystems and equipment should be electrically bonded to provide a 2.5 mΩ bond in accordance with MIL-STD-464C.
4.28 Appropriate electrical bonding minimises E3 susceptibility of aircraft systems and equipment. Electrical bonding is common practice in aircraft wiring and electrical/electronic systems and equipment, and is comprehensively covered in Authority recognised Airworthiness Codes. While the actual bond resistance between systems and equipment that will ensure safe flight is not impacted is system dependent, a 2.5 mΩ bond between metal surfaces has been demonstrated to ensure that RF potentials between systems and equipment will not adversely affect system operation.
4.29 Design Requirement (Essential). Defence aircraft must be able to be connected to an external ground.
4.30 External grounding of the airframe is used to control current flow and static charge/discharge paths when the aircraft is on the ground. External grounding minimises hazards associated with personnel electric shock, and inadvertent ignition of ordnance, fuel and flammable vapours.
4.31 Design Requirement (Recommended). Requirements for maintaining the E3 hardness of Defence aircraft during in-service operations and support should be established using the guidance in MIL-STD-464C.
4.32 Authority recognised Airworthiness Codes may not prescribe requirements to maintain the E3 hardness levels established by the initial design, so they are not compromised by inadequate life-cycle support including maintenance, repair, surveillance and corrosion control. These requirements are comprehensively covered in MIL-STD-464C, and provide specific consideration of E3 issues when formulating ICA and when determining the most appropriate support program to manage in-service support E3 issues.
4.33 In addition to the applicable airworthiness design requirements prescribed in the preceding section of this Chapter, this section presents Authority prescribed E3 airworthiness design requirements for changes to Defence aircraft type design, noting that any change must be considered within the context of the Defence aircraft’s CRE.
4.34 Design Requirement (Essential). Modifications to Defence aircraft systems, subsystems and equipment must comply with the E3 airworthiness design requirements prescribed in the aircraft’s certification basis.
4.35 Design Requirement (Recommended). Modifications to Defence aircraft systems, subsystems and equipment should comply with the E3 design requirements prescribed in MIL-STD-464C.
4.36 To avoid the introduction of EMI/EMC hazards, particularly for safety of flight systems and equipment, design changes to Defence aircraft must not compromise the extant the level of E3 hardness established by the certified aircraft design. Potential impact on E3 hardness should be identified during development of changes to Defence aircraft designs, and design treatments must be implemented for any reduction. Where reasonably practicable, changes to Defence aircraft designs should incorporate E3 protection improvements by following the design principles in MIL-STD-464C.
4.37 Design Requirement (Essential). Requirements for maintaining the E3 hardness of Defence aircraft modifications during in-service operations and support must be established using the guidance in MIL-STD-464C.
4.38 E3 hardness levels established during design of Defence aircraft modifications must not be compromised by inadequate life-cycle support including maintenance, repair, surveillance and corrosion control. Requirements for maintaining E3 hardness throughout the life-cycle of Defence aircraft are comprehensively covered in MIL-STD-464C, and provide specific consideration of E3 issues when formulating ICA and when determining the most appropriate support program to manage in-service support E3 issues.
4.39 Compliance with all of the Authority prescribed E3 airworthiness design requirements in this Chapter would ensure that mission systems will not be impacted by E3. However, this level of compliance would come with substantial costs in both design and certification effort that may not be commensurate to the risk associated with mission system failure. For example, depending on the Defence aircraft mission profiles, mission systems may not be exposed to the potential worst-case EME, and verifying that mission systems can operate within this EME would not be warranted. Consequently, considerable tailoring of the requirements is likely to be warranted to ensure that mission systems will function correctly when required, without imposing the additional verification evidence requirements associated with safety of flight systems and equipment compliance.
4.40 This section presents guidance on tailoring that may be appropriate for ensuring that mission systems in Defence aircraft are not adversely impacted by E3.
4.41 As previously discussed, margins allow for inherent differences in equipment build quality and installations, and variability in test methods and outcomes. The application of margins, however, imposes additional testing and/or design development costs to ensure that the margin is achieved. For mission systems, these additional requirements are only likely to be warranted where the loss of capability would be unacceptable if the certified EME is exceeded.
4.42 Capability Design Requirement. Margins for mission systems should be established on the basis of the criticality of the system to the achievement of the required capability.
4.43 Since missions systems, by definition, are not critical to safe flight, requiring these systems to be capable of withstanding the EME defined in MIL-STD-464C (or the EME associated with Defence’s role and operating environment) may not be warranted. To ensure that an appropriate EME is defined for mission systems, the Defence aircraft mission profiles should be evaluated to establish whether mission systems that support a critical capability will be exposed to the worst-case EME established for the aircraft’s CRE. Where this is the case, the mission systems should be verified as being capable of continued operation when exposed to this EME. Otherwise, the mission systems’ ability to withstand the potential EME that they are likely to be exposed to should be verified.
4.44 Capability Design Requirement. The EME that mission systems should be certified to withstand should be established during design development and compliance verified during design certification.
4.45 Current civil requirements for ‘mission systems’, ie those systems not required for safe flight, do not mandate certification to the EME defined in the associated Airworthiness Codes or AMC. For example, the FARs do not prescribe compliance with the requirements for continued functionality in the defined HIRF environments for non-essential systems and equipment. Consequently, this equipment may only be certified to withstand an EME as low as 1 V/m, which is clearly below a level that would be acceptable for Defence mission systems. Where verification of mission systems EME certification was, or is proposed to be, based on civil design requirements, verification activities must be critically evaluated to confirm the EME levels applied to mission systems are appropriate.
4.46 EMSEC requirements for Defence are published by the Australian Signals Directorate in Australian Communications – Electronic Security Instructions (ACSI) 71(C). EMSEC does not impact safety of flight, and the need for EMSEC is a capability requirement driven by the Defence aircraft’s CRE.
4.47 Capability Design Requirement. Where required, Defence aircraft EMSEC should comply with the requirements of ACSI 71 (D), Annex D.
4.48 Control of system emissions may be required to support operations in close proximity to other platforms and to limit threat capability detection and tracking. Similar to the requirement for EMSEC, EMCON is a capability requirement driven by the Defence aircraft’s CRE.
4.49 Capability Design Requirement. Where required, Defence aircraft EMCON should comply with the requirements of MIL-STD-464C.
4.50 EM spectrum approvals for Defence aircraft systems are managed by the Defence Spectrum Office in accordance with the requirements of the Defence Spectrum Manual. Approval of RF spectrum use should be achieved prior to Defence aircraft operations.
4.51 Capability Design Requirement. Defence aircraft EM spectrum approval should be provided in accordance with the requirements of the Defence Spectrum Manual.
4.52 While not essential for the achievement of a safe aircraft design from an E3 perspective, Defence experience has demonstrated that a successful E3 certification and control program depends on appropriate and sufficiently detailed planning. Consequently, the Authority recommends the use of an E3 planning document (the E3 Control Program Plan (E3CPP)) to assist designers to achieve an E3 compliant design, while limiting test and analysis overheads to only those required for the specific certification activity under consideration.
4.53 An E3CPP should be developed for all new Defence aircraft acquisitions, and for all Major modifications that could have a substantial impact on E3 certification. The E3CPP should include a description of the following:
the proposed management framework for the E3 control program
the Defence aircraft EME
E3 design and mitigation strategies considered for incorporation or incorporated into the aircraft design
the tests and analyses required to support E3 certification, together with references to any test results
any E3 shortfalls identified, which could not be treated by design, and any associated alternative risk treatment strategies employed.
4.54 Exposure to radiation emitted by Defence aircraft systems and equipment can result in serious health issues. Defence must comply with Commonwealth WHS legislation for the purposes of ensuring the safety of persons in the workplace. Defence’s radiation safety requirements for personnel are prescribed in the Defence Radiation Safety Manual, which requires compliance with the Australian Radiation Protection and Nuclear Safety Act 1998. Additional compliance requirements for Defence are prescribed in the Defence Work Health and Safety Manual, Volume 2, Part 3C, Chapters 1-4. The safety of both aircraft occupants and personnel outside of the aircraft must be ensured and personnel safe distances, defined in accordance with the requirements of the Defence Radiation Safety Manual, must be established for RF emitters fitted to Defence aircraft.
4.55 Further guidance on E3 design considerations and the application or tailoring of E3 design requirements for Defence aircraft mission systems and equipment can be provided by the chapter sponsor.