13.1 This chapter provides airworthiness design requirements for Defence aircraft propulsion systems. This chapter is applicable to crewed aircraft and certified-category uncrewed aircraft. Within the context of the DASR and this chapter, DASA defines the aircraft propulsion system as including but not limited to the engine and propeller, including sub-systems, accessories and controls. For aircraft powered by reciprocating engines, auxiliary power units, or other turbomachinery, the applicant should seek DASA advice as to whether the content of this chapter is applicable. DASA advice should be sought as to the extent this chapter is applicable to:
aircraft powered by reciprocating engines; or
auxiliary power units and other turbomachinery.
13.2 This chapter is not applicable to propulsion systems fitted to munitions.
13.3 The airworthiness codes recognised by DASA (refer Section 1 Chapter 3) provide an appropriate benchmark for establishing and maintaining an adequate level of safety for aircraft propulsion systems. However, DASA has identified the following three circumstances where recognised airworthiness codes may require supplementation:
Propulsion system environment requirements in some civil airworthiness codes are assessed as inadequate for the Defence CRE.
Novel propulsion system configurations or technologies are used that may not be adequately covered by current recognised airworthiness codes.
The nature of proposed military operations dictates the need for more complex and proactive in-service propulsion system integrity management (over and above that contained in some airworthiness codes) to ensure risk of failure remains within that inherent in the Type Certification Basis (TCB).
13.4 The requirements and associated discussion in this chapter are framed around these circumstances. When developing a certification basis for a Military Type Certificate (MTC), Major Change or Military Supplemental Type Certificate (MSTC), each applicant will need to assess the airworthiness design requirements inherent in the baseline Primary Certification Code (PCC) or standard and supplement or tailor, as required, using the requirements in this chapter. Applicants are highly encouraged to engage early with DASA as part of this process. Note that three likely scenarios exist for any given DASDRM requirement:
Intent of DASDRM requirement is not met by any requirement in the underlying PCC / standard. In this case, the applicant would need to supplement the PCC / standard to add a new requirement.
Intent of DASDRM requirement is partially met by an existing requirement in the underlying PCC / standard. In this case, the applicant may tailor the existing requirement so that it meets the full intent of the DASDRM requirement.
Intent of DASDRM requirement is fully met by an existing requirement in the PCC / standard. In this case, the applicant may propose to DASA that no supplementation or tailoring is required.
13.5 Separate to the DASA-prescribed airworthiness requirements under the DASR and DASDRM, it is Defence Policy11 that each Defence-registered aircraft type have an effective and efficient Propulsion System Integrity Program (PSIP) to:
ensure, so far as is reasonably practicable, that degradation of integrity does not present risks to health and safety
contribute to delivery and assurance of capability
support cost-effective sustainment of capability.
13.6 Under Defence Policy, the Defence-preferred approach for PSIP is alignment with MIL-STD-3024; a cradle-to-grave management framework for propulsion system integrity that encompasses system requirements, design, verification and sustainment. Despite the fact that the PSIP remit and objectives are broader than safety, an effective PSIP is key to supporting the essential design requirements set out in this chapter.
13.7 The PSIP for each aircraft type should be documented in a Propulsion System Integrity Management Plan (PSIMP). PSIMPs are key documents that assist applicants and the regulated community by maintaining a record of relevant propulsion system certification information and data, and demonstrate how the PSIP complies with the design requirements prescribed in this chapter and supports related DASR obligations22.
13.8 TCB Foundation. As outlined above, the airworthiness codes recognised by DASA provide an appropriate benchmark for developing a TCB for aircraft propulsion systems, subject to supplementation and / or tailoring33 to address the requirements provided in this chapter and any unique Defence CRE aspects.
13.9 For cases where Defence is acquiring a propulsion system where the baseline design requirements are not a recognised airworthiness code, then applicants are recommended to use the European Military Airworthiness Certification Criteria (EMACC) Handbook, in conjunction with this chapter, to develop and propose for Authority approval a comprehensive set of airworthiness design requirements for propulsion system certification. Applicants are highly encouraged to engage early with DASA if this is the case.
13.10 Civil-Certified Propulsion Systems. In some cases, additional design requirements, or additional compliance evidence for existing design requirements, may be required for civil-certified propulsion systems to account for the Defence CRE. For example, this could be applicable for military-specific configuration additions such as engine air particle separators, signature suppression systems or afterburner modules, and military-specific environments such as armament gas ingestion, armament vibration, military threats (e.g. electromagnetic or ballistic) and more severe sand, dust, corrosive and icing conditions.
13.11 Novel Propulsion System Technologies. The aviation industry is actively pursuing novel propulsion system technologies such as distributed engine configurations, electric and electric-hybrid energy sources and adaptive-cycle turbine engines. Whilst the near-term intended applications for many of these novel technologies is the light and very light aircraft segments, novel technologies will inevitably be used in Defence aircraft. The current airworthiness codes recognised by DASA do not adequately address the full scope of design requirements that would be necessary to certify most of these novel technologies. Whilst some Authorities are working on special conditions, these are mostly for individual applications or may not cover the categories of aircraft that Defence may acquire.
13.12 Therefore, where a novel propulsion system technology is to be employed for a Defence aircraft, suitable design requirements must be identified and proposed to DASA for approval.
13.13 For propulsion system products and their respective systems integration aspects, Defence’s type certification approach almost exclusively relies on fully or partially leveraging prior NAA/MAA certification. Performing a CRE Assessment (CREA) is an essential part of this process to ensure the prior certification is applicable for the Defence CRE and the design is safe for the intended Defence use.
13.14 Failure modes for propulsion systems (in particular fatigue) can be highly sensitive to small changes in usage, loads and environment. Therefore, CREAs for propulsion systems usually require detailed and quantitative analysis. Applicants for a MTC who are leveraging prior NAA/MAA certification should undertake an initial ‘mission analysis’44 , as described below under the Ongoing Monitoring and Periodic Assessment section, in order to satisfy the propulsion system aspects of the CREA requirement (refer DASR GM 21.A.20).
13.15 The propulsion system critical parts and associated Airworthiness Limitations (AwLs), consistent with the TCB and the intended Defence CRE, must be identified during type certification (refer DASR AMC 21.A.41).
13.16 Variations in actual aircraft usage, environment and configuration can have a significant impact on when propulsion system critical part AwL actions (such as component retirement or inspections) need to be performed. This is especially the case for military operations where there is typically higher variability in mission profiles compared to the civil sector.
13.17 The airworthiness codes recognised by DASA vary in terms of life tracking requirements. For example, civil airworthiness codes require AwLs to be identified55, however, they do not sufficiently address requirements for tracking life accrual necessary in the military context. DASA therefore prescribes the following essential airworthiness design requirement:
13.18 Design Requirement (Essential). The process for tracking life accrual of propulsion system critical parts shall be defined, commensurate with the complexity of the corresponding AwL requirements.
13.19 AwLs include, and will define, the lifing metric(s) and any algorithm, equation, factor(s) or other engineering data, which must be used to calculate life accrual. The complexity of the process for tracking life accrual of propulsion system critical parts will vary based on the complexity of the AwL definition.
13.20 In many circumstances, the process for tracking life accrual of propulsion system critical parts will require a dedicated system. In this context, the ‘system’ will typically comprise on-board and off-board hardware and software for data recording, processing and analysis, as well as the associated procedures66. The philosophy and design of the system must be based on the: certification basis; the propulsion system type and role; the nature and definition for each AwL; anticipated operational variability (i.e. mission profile and mission mix variability) and uncertainty around ADF CRE. The following considerations should also be taken into account by applicants:
The system must ensure that the accomplishment of AwL actions for individual components takes into account the applicable parameters that contribute to life degradation.
The system must have the ability to capture the necessary input data from all ground and flight operations (including development and / or acceptance testing) from the entry into service through to the retirement of each engine or propeller.
The system must have the ability to identify and appropriately account for any missing or invalid data.
The system must have the ability to track critical part life accrual per individual component, per module or per engine as required. The level of tracking and serialisation fidelity must ensure that individual critical parts do not exceed the underlying basis of AwLs.
Requirements must ensure the system will be validated prior to fielding. Validation should test the entire system (on-board and off-board elements) in an end-to-end fashion (i.e. from raw / input data through to the AwL lifing metric outputs). Validation should ensure that the specified system will produce reliable, repeatable and suitably conservative outputs so that AwLs are not exceeded in-service.
13.21 Compliance with this design requirement should be demonstrated through system validation / test report(s), and documentation that defines the process, and where relevant, the dedicated system. These should also be included, either directly or via reference, in the PSIMP.
13.22 Once in-service, the CAMO must maintain a record of the current status of service life limited components (i.e. track life accrual against AwLs to meet continuing airworthiness obligations - refer DASR M.A.305(d)(4)). Compliance with the essential design requirement above will ensure that the requirements and process for tracking life accrual of propulsion system critical parts are clearly defined up-front as part of type certification.
13.23 The following references also provide useful information on propulsion system life tracking requirements:
MIL-HDBK-516C (Airworthiness Certification Criteria), section 7.2.3.6
MIL-HDBK-1783B Change 2 (Engine Structural Integrity Program (ENSIP)), sections A.4.19, A.5.19.c and A.5.19.d.
13.24 During design of a propulsion system, OEMs develop critical part AwLs based on predicted engine operation, material behaviour and environment. The OEM’s design assumptions77 are typically based on the intended aircraft role(s) and cannot always specifically account for each operator’s individual usage, environment and configuration throughout the entire life-cycle of a propulsion system. This is especially the case for military operations as roles, tactics and operating environments for a given propulsion system can vary significantly between operators and evolve over time. For military aircraft, monitoring accrual of lifing parameters against AwLs alone is insufficient to ensure that engines continue to operate within the risk level inherent in the TCB.
13.25 The term ‘mission analysis’ is used to describe the process of:
collection of parametric flight data needed to define the operating and environmental conditions that can impact propulsion system critical part AwLs,
periodic assessment of this data to determine if the current critical part AwLs remain valid for the operator, and
as required, calculation of new critical part AwLs based on updated design assumptions that reflect actual and anticipated usage and environment.
13.26 The airworthiness codes recognised by DASA vary in terms of requirements that meet the intent of mission analysis. DASA therefore prescribes the following essential airworthiness design requirement:
13.27 Design Requirement (Essential). A plan for ongoing monitoring and periodic assessment (mission analysis), as necessary to ensure the continued integrity of propulsion system critical parts, shall be documented.
13.28 The mission analysis philosophy and details will vary significantly based on the propulsion system type and role, anticipated operational variability, certification basis and design philosophy. The following considerations should be taken into account by applicants when documenting the mission analysis plan:
The usage and environmental parameters that need to be monitored in-service, plus any other input data requirements, must be defined. Data requirements should be based on advice from the relevant OEM or organisation capable of conducting the mission analysis.
System requirements must be established to enable collection of the required usage and environmental parameters. Note that there may be a high degree of commonality between the parameters and system required to collect data for mission analysis and that required for critical part life tracking. The system requirements should include mechanisms to ensure that the data collected is:
accurate and valid; and
representative of all ADF operations and environments (if the entire fleet is not going to be continuously monitored).
The plan must ensure that detailed and quantitative analysis will be conducted to compare actual ADF usage and environment parameters to design assumptions and ensure that any impact(s) on critical part AwLs will be identified. For this reason, the conduct of mission analyses should be undertaken by the OEM, or an appropriately competent and experienced organisation with access to the necessary type design data.
The plan must ensure that all propulsion system critical parts and all AwL aspects will be sufficiently covered, including mandatory life limits and inspection requirements, and any algorithm, equation, factor(s) or other engineering data that is used to calculate life accrual against AwL intervals.
The plan must ensure that mission analysis outputs will either:
explicitly confirm that critical part AwLs remain appropriate for the Defence CRE and for preventing occurrence of hazardous propulsion system effects, or
as required, provide updated critical part AwLs (including any algorithm, equation, factor(s) or other engineering data to calculate life accrual) along with the substantiation necessary to approve the updated AwLs under DASR 21.
The plan must document the organisational and contractual or international arrangements (including data sharing agreements) that are present to ensure that the plan is implementable.
The plan must ensure that mission analyses will be conducted at a frequency that ensures the effective certified lives / intervals will not be exceeded, even in the case of a significant underestimation of actual usage severity. The frequency of routine mission analysis may need to vary throughout life of the aircraft based on CRE evolution, and dedicated mission analysis should be conducted whenever a significant CRE change is planned. Ongoing monitoring of usage and environment parameters should be conducted to identify any CRE changes that may trigger an amended mission analysis schedule.
13.29 Compliance with this requirement should be demonstrated by documentation that defines the mission analysis plan or statement of work. This should also be included, either directly or by reference, in the PSIMP.
13.30 Once in-service, the MTCH must ensure the continued integrity of the propulsion system through ongoing monitoring and periodic assessment (i.e. as a continued airworthiness obligation - refer DASR 21.A.44(c)). Compliance with the essential design requirement above will ensure that the plan for propulsion system ongoing monitoring and periodic assessment are clearly defined up-front as part of type certification.
13.31 The following references also provide useful information on propulsion system mission analysis (or equivalent terminology) requirements:
MIL-STD-3024 Change 1 (Propulsion System Integrity Program (PSIP)), section 5.1.4.1.6
MIL-HDBK-1783B Change 2 (Engine Structural Integrity Program (ENSIP)), sections A.4.19 and A.5.19.b
EASA AMC E 515 (Engine Critical Parts), section 3(g)
FAA AC 33.70-1 Change 1 (Guidance Material for Aircraft Engine Life Limited Parts Requirements), section 8.g.
13.32 Further guidance on implementing the propulsion system requirements prescribed in this chapter can be provided by the chapter sponsor.