7.1 Fires represent one of the most severe hazards that can occur in an aircraft. Fire protection measures are therefore essential design characteristics in aircraft that minimise the likelihood of a fire occurring and, where a fire does occur, ensure that the crew are alerted to the presence of and can effectively combat the fire, and if necessary take action to land and evacuate the aircraft.
7.2 For the majority of Defence aircraft the fire protection design requirements prescribed in Authority recognised civil and military Airworthiness Codes defined in Section 1 of this manual satisfy prescribed safety objectives for Defence aircraft fire protection. However, modifications to civil aircraft to provide military capability may be inconsistent with the ‘normal’ approach to fire protection adopted within civil Codes, and therefore the level of fire protection afforded by the design may be compromised. Consequently, the Authority prescribes fire protection airworthiness design requirements to supplement the civil Codes and provide a basis for verifying the acceptability of Defence aircraft fire protection measures.
7.3 This Chapter presents Authority prescribed airworthiness design requirements for Defence aircraft fire protection.
7.4 Where a Defence civil-derivative aircraft is substantially unmodified from that originally certified by an Authority recognised National Airworthiness Authority (NAA), compliance with an Authority recognised civil Airworthiness Code defined in Section 1 will satisfy the prescribed fire safety objectives for Defence aircraft. Military aircraft certified by an Authority recognised Military Airworthiness Authority (MAA) are designed from first principles to provide the required capability and all associated systems and equipment needed to support military functions will have been subjected to the associated military Code fire protection design requirements for that aircraft type. Any modifications to military aircraft that are subject to MAA certification, will similarly be certified under this ‘first principles’ approach. Consequently, for Defence military aircraft compliance with the fire protection design requirements in an Authority recognised military Airworthiness Code satisfies prescribed fire safety objectives for Defence aircraft.
7.5 Design Requirement (Essential). Defence aircraft must satisfy the fire protection design requirements prescribed in an Authority recognised Airworthiness Code as defined in Section 1 of this manual.
7.6 Notwithstanding compliance with a civil Airworthiness Code, civil-derivative aircraft that are modified to provide military capabilities may have additional equipment and systems fitted in areas of the aircraft where such equipment is not usually accommodated. Civil-derivative aircraft modifications may also include equipment that does not comply with the materials properties usually applied to aircraft equipment to provide adequate fire protection. In this case, compliance with the fire protection design requirements of an Authority recognised civil Airworthiness Code may not afford a level of fire safety that satisfies prescribed safety objectives. Where a Defence civil-derivative aircraft configuration includes modifications from the original certified baseline design to include systems/equipment that is not ‘normal’ (ie similar in function and hazards) to the original certified aircraft design, the Authority prescribed fire protection airworthiness design requirements defined in this chapter must also be met.
7.7 The Authority prescribed fire protection design requirements ensure that military-unique modifications to civil-derivative aircraft do not unacceptably degrade the inherent level of fire protection afforded by the original civil certified design. Fire protection design requirements prescribed in civil Airworthiness Codes may not account for the modified design; for example, high powered electrical and electronic equipment installed in compartments which do not usually accommodate such equipment may pose ignition hazards that are not adequately treated within civil airworthiness design requirements for electrical and electronic bays. To verify the acceptability of the fire protection measures in a Defence civil-derivative aircraft, any unique features must be analysed to evaluate their impact on the level of fire protection afforded by the design.
7.8 To ensure that airworthiness design requirements for fire protection account for the potential hazards that may be present as a result of military modifications to Defence civil-derivative aircraft, the Authority prescribes design requirements based on the fundamental fire protection concepts of fire prevention, fire detection and fire suppression. Modified Defence civil-derivative aircraft designs may pose the following hazards that could compromise the adequacy of fire protection design requirements in civil Codes:
unusual military configurations not normally present in civil aircraft designs that introduce new or additional fuel sources, eg the use of commercial equipment to provide a military capability that is manufactured from materials that do not comply with contemporary fire prevention standards for civil aviation (compromised fire prevention);
the presence of ignition sources, eg high power electrical/electronic equipment, that are unlikely to be found in civil aircraft systems, or are located in areas of the aircraft where ignition sources are not normally found (compromised fire prevention);
the absence of a means by which the presence of fire is notified to the crew in a modified area of the aircraft, eg lack of fire detection due to no requirement for detection in civil aircraft electrical and electronic bays (compromised fire detection); and
a lack of access to the compartment in which the modified equipment is located, which may impede evaluation and suppression of a fire (compromised fire suppression).
7.9 Any one or combination of the hazards associated with modifications in Defence civil-derivative aircraft identified in paragraph 7.8 may result in a marked degradation of fire protection requiring treatment. Consequently, each aspect of proposed modifications must be evaluated to clearly establish if fire protection attributes have been compromised and if additional risk treatment is warranted. This section presents the Authority prescribed fire protection airworthiness design requirements for fire prevention, detection and suppression in Defence civil-derivative aircraft.
7.10 Fire prevention is usually achieved in civil Airworthiness Codes by treating hazards associated with ignition and fuel. Fire prevention may be achieved through combustible materials hazards reduction (flammability), installation hazards reduction (reducing ignition sources), isolation and separation (of fuel and ignition sources), ventilation, cooling, drainage, electrical bonding and lightning protection. The effectiveness of two of these fire prevention elements, namely materials flammability and reducing or isolating/separating ignition and fuel sources, may be reduced as a result of modifications in civil-derivative aircraft.
7.11 Fire protection requirements in civil Airworthiness Codes rely on the behaviour of materials in the presence of an ignition source (limiting the potential for the material to ignite) and the ability of the material to sustain a fire once it is ignited (self-extinguishing properties). However, military-unique modifications in civil-derivative aircraft may include equipment containing materials that do not comply with contemporary flammability requirements and may compromise the extant fire protection afforded by the aircraft design. Such shortfalls may not be unacceptable to Defence, provided the overall fire protection of the aircraft is not compromised. Consequently, the Authority has prescribed the following design requirement to ensure such equipment is identified, and its impact on fire protection is assessed.
7.12 Design Requirement (Essential). Material properties of equipment used in modifications to Defence civil-derivative aircraft must comply with the applicable flammability requirements prescribed in an Authority recognised Airworthiness Code.
NOTE
A ‘systems’ approach is required to establish if the level of fire protection afforded by modified Defence civil-derivative aircraft satisfies fire safety objectives. This consists of identifying additional hazards posed by the design (ie fuel and ignition sources), then determining whether the extant fire detection and suppression is adequate or if additional detection and/or suppression is warranted. Consequently, non-compliance with the materials flammability requirements may not require resolution through design change to incorporate compliant materials, but may be adequately treated through enhanced (or existing) fire detection and suppression.
7.13 Military-unique modifications in civil derivative aircraft may also include ignition sources in locations on an aircraft where such sources are not normally present, or where the ability to isolate/separate the ignition source from fuel is limited, which may increase the likelihood of ignition. Such configurations may undermine the basis of, or impose additional fire hazards not accounted for in, the civil Codes (for example, the configuration may now be considered an electrical and electronic bay (EE bay) and fire protection considerations may therefore be limited). The impact on fire safety associated with changes to potential ignition sources, particularly where the source cannot be isolated or separated from fuel sources, must be evaluated. Consequently, the Authority has prescribed the following airworthiness design requirement to ensure that ignition sources introduced by military-unique modifications to Defence civil-derivative aircraft do not unacceptably compromise fire safety.
7.14 Design Requirement (Essential). Where modifications in Defence civil-derivative aircraft include ignition sources that are not normally found in that location on civil certified aircraft (and therefore potentially are not accounted for within a civil Airworthiness Code), the level of fire safety in the presence of the ignition source must be demonstrated, through a systems safety analysis, to meet prescribed fire safety objectives.
7.15 Fire detection provides the crew with notification of a potential fire. The detection method may use a purpose-designed smoke and/or fire detector system or an indirect means such as visual monitoring or smell. In either case, the means used must provide notification to the crew of a fire with adequate time to respond to and extinguish the fire before it becomes established. Civil aircraft fire detection requirements are predicated on the ability of materials, which comply with contemporary flammability requirements, to be self-extinguishing once the ignition source is removed or, where this is not possible, to provide the crew with sufficient time to conduct effective fire suppression actions. However, fire detection systems may not be required for certain types of hidden compartments in civil aircraft (for example, civil Airworthiness Codes do not normally require fire detection in EE bays).
7.16 The effectiveness of fire detection in modified Defence civil-derivative aircraft may be compromised where the properties of materials reduce the time between ignition and a fire becoming established, or the modification impacts the effectiveness of the detection means implemented in the original civil design for that compartment or area of the aircraft (for example, additional ignition sources that increase the likelihood of a fire). Consideration of fire detection in addition to that normally required through compliance with the civil Codes would only be required where the military-unique modification resulted in an ‘unusual’ configuration within a compartment of the aircraft where a fire is unlikely to be detected via other means (eg vision or smell). For example, fitment of electrical equipment in hidden or inaccessible compartments not normally fitted with this equipment may pose additional ignition hazards that require treatment through fitment of purpose-designed fire detection.
7.17 Fire detection in Defence civil-derivative aircraft designs must ensure that notification of ignition is provided with adequate time for the crew to undertake the required fire suppression actions (for example, removal of power from equipment). Consequently, the following fire detection design requirement is prescribed by the Authority.
7.18 Design Requirement (Essential). Modified compartments of Defence civil-derivative aircraft may result in the presence of materials or additional ignition sources not normally located in that compartment on civil certified aircraft. In these cases, the means of detecting a fire must be verified as providing adequate notification to the crew, or purpose-designed fire detection that complies with the following must be fitted:
MIL-HDBK-516C, Section 8.4.7 Fire Detection, and Section 8.4.20 Detection and Control of Overheating, or
DEF STAN 00-970 Section 4.26.24 Fire Detection and Warning.
7.19 Fire suppression may be provided through indirect or purpose-designed means. Indirect fire suppression is afforded through timely notification of a fire and crew action to remove the ignition source, which in turn extinguishes the fire. Purpose-designed fire suppression, on the other hand, provides the crew with the ability to directly combat a fire, usually through the application of an extinguishing agent. Purpose-designed fire suppression may be required where the time taken to alert the crew to an ignition, and for the ignition source to be removed, exceeds the time that the fire prevention measures remain effective, or where the fuel and/or ignition sources cannot be removed (eg engine bays).
7.20 Fire suppression requirements in the civil Airworthiness Codes may not take into account unusual features of a military modification in inaccessible compartments of Defence civil-derivative aircraft (for example, materials that are not self-extinguishing following removal of the ignition source). Consequently, the Authority has prescribed the following fire suppression design requirement.
7.21 Design Requirement (Essential). The ability of crew to remove sources of ignition following notification of a fire must be verified as providing effective fire suppression in modified inaccessible compartments of Defence civil-derivative aircraft, or purpose-designed fire suppression that complies with the following NAA airworthiness design requirements must be fitted:
USAF. MIL-HDBK-516C, Section 8.4 Fire and Hazard Protection, or
UK MoD. DEF STAN 00-970, Section 4.26 Fire Precautions.
7.22 Fire protection design requirements for civil aircraft, particularly large fixed wing aircraft (ie FAR 25 and CS 25) include requirements for fuel tank ignition prevention and fuel tank flammability assessment and, for those aircraft where fuel tank flammability exceeds the defined threshold, flammability reduction means. There are a number of circumstances under which compliance with the fuel tank flammability requirements may not be achieved for Defence civil-derivative aircraft (for example, acquisition of used aircraft where retrospective compliance is not required, or an ‘administrative’ dispensation granted by a civil NAA for military aircraft). Non-compliance with these requirements could lead to an unacceptable degradation in fuel tank fire safety. Consequently, the following design requirement is prescribed by the Authority.
7.23 Design Requirement (Essential). Defence civil-derivative aircraft must comply with requirements for fuel tank ignition prevention and flammability in FAR/CS 25.981, and FAR/CS Part 25 Appendix M Fuel Tank Flammability Reduction Means and Appendix N Fuel Tank Flammability Exposure.
7.24 Further guidance on Defence aircraft fire protection requirements prescribed in this chapter can be provided by the chapter sponsor.