In April of 2021, EASA first published their Certification Review Item (CRI) Consultation paper on Special Condition (SC) E-19 on the subject of Electric/Propulsion Systems (EHPS). The SC was developed to support applications to EASA for the certification of Electric and/ or Hybrid Propulsion Systems powered by propulsion batteries and/ or fuel, including those as part of an aircraft or as an engine product and dedicated to a known intended aircraft application.
Due to the ongoing nature of the advanced mobility sector, several complements to the SC19 have been proposed, including the proposed Level 2 Means of Compliance (MoC). These MoC are: Overspeed and Containment Demonstration, Endurance and Durability Demonstration (A), Calibration Assurance, and Safety Assessment.
These proposals have been open for consultation until April 30, 2025. The following article summarises the MoCs that were in review. This summary has been developed for information, education and training purposes only. For any doubts on the rules and MOCs, please refer to them, or write to us for support or clarification.
Overspeed and Containment Demonstration
This document provides proposed MoCs to support certification under SC EHPS.240 (Overspeed and Rotor Integrity) and EHPS.250 (Rotating Parts Containment) for EHPS. It aims to fill the regulatory gap for emerging electric and hybrid engines in the absence of traditional certification specifications, enabling safe innovation while maintaining robust safety standards.
It applies to electric, reciprocating, and turbine engines and includes methods to determine the necessary testing speeds and containment expectations. For VTOL Enhanced Category aircraft using electric engines driving fans, compliance must also be shown for VTOL.2240 (d) and it’s associated MoC High Energy Fragments – Particular Risk Assessment (6) and VTOL 2510 (a) (1) Equipment, systems and installations.
EHPs.240 Overspeed and Rotor Integrity
This entails that a rotor overspeed must not result in rotor burst, rotor growth or other damage that could result in a Hazardous EHPS effect. These are required to be proven via test, validated analysis or both. The rotors must also be proven to have an adequate strength margin with respect to the burst, growth and damages that could become a hazardous EHPS effect.
EHPS.250 Rotating Parts Containment
This states that the failure of any rotating component or part of the equipment, electric engine or generator must not lead to the release of high-energy debris. It also covers that if the EHPS includes a compressor or a turbine, after any failure, it remains contained and that no Hazardous EHPS Effect can occur or other damage as a result before the EHPS is shut down due to blade failure.
To demonstrate compliance, two primary strategies have been proposed:
Methodology 1 – Combined Demonstration
To demonstrate EHPS.240 and EHPS.250 together under the assumption that the rotor integrity is proven via High Energy Debris (HED) containment or above Maximum Reachable Speed (MRS). This requires an analysis of worst-case material properties and tolerances and includes safety aspects such as fire prevention and structural integrity.
The demonstration must also cover not only the prevention of HED release but also the absence of Hazardous EHPS Effects, as required for compliance with EHPS.250(a).
The demonstration not only of the non-release of HED but also of the absence of Hazardous EHPS Effects as part of the showing of compliance to EHPS.250(a).
Methodology 2 – Separate Demonstration
To demonstrate EHPS.240 (overspeed) and EHPS.250 (containment) independently. This follows guidance from CS-E standards and adapts testing speeds based on rotor configurations.
Based on the MoC, there are certain considerations that must be taken into account for VTOLS. For VTOL Enhanced Category aircraft, debris containment from a fan disk burst must not result in catastrophic effects. Compliance can follow either methodology but must meet stricter probability thresholds for failure (<10⁻⁹ FH) and ensure safe operation even after a fan disk burst.
The MoC also includes engine-specific guidance. For reciprocating engines, use CS-E 400 (EHPS.240) and CS-E 80 (d) (EHPS.250). For turbine engines, use CS-E 840 for EHPS.240 and CS-E 80/810 for applicable EHPS.250 elements. EHPS.250(a) is not directly applicable to turbine engine rotors.
Endurance and Durability Demonstration (A)
In this section, the proposed MoC to SC E19 is related to 3 EHPS requirements: EHPS.40 defines the operational ratings and limits, EHPS.420 demonstrates system durability under those limits and EHPS.450 ensures post-test airworthiness through inspections.
EHPS.40 – Ratings and Operating Limitations
This section defines how to establish Electric Hybrid Propulsion Systems’ ratings and operating limits (EHPS). It draws from CS-E 40 (Certification Specifications for Engines) and extends it to accommodate new propulsion architectures, such as distributed propulsion and hybrid systems.
The EHPS must have clearly defined and EASA-approved ratings and operating limitations to ensure safe operation under all conditions, including specifications for Take-off, Maximum Continuous, and Emergency Power/Thrust ratings with their permitted durations. These ratings must reflect the lowest performance levels that all affected sub-systems can reliably deliver throughout operation, and include defined transient exceedances and associated emergency failure conditions.
EHPS.40 uses a mission-phase-based approach (take-off, climb, cruise, etc.) to define rating structures and power demands. This includes assessing minimum engine performance over time, considering variation and degradation.
As a special consideration, hybrid EHPS using certified piston engine, turbines or Auxiliary Power Units (APU) can take credit for their pre-approved ratings and limitations.
The MoC lists the following standards to be used when proposing the verification methods for the EHPS.40:
EUROCAE ED-321: provides Guidance on the intend of EHPS.420 and the strategy to demonstrate compliance to the endurance substantiation. The document also provides some guidance to other requirements in the context of the endurance demonstration, including EHPS.40.
IEC60034-1_ed13: provides Guidance on the concept of duty Cycle.
EHPS.420 – Endurance Demonstration
The endurance demonstration ensures the EHPS can reliably deliver the declared ratings over its intended operational life, especially under extreme usage conditions.
The EHPS must undergo a rigorous endurance demonstration that reflects its design and intended use, covering all operational limits with adequate cycles and power settings to prove safe service operation. Additionally, for both Normal and Inadvertent Transient EHPS Exceedances, approval requires evidence that the system can operate at peak transient conditions of the affected parameters without maintenance, except for correcting any failure that caused the inadvertent exceedance.
This requirement confirms the aircraft’s safe and reliable performance while establishing its operating limits and system durability and supporting the certification of transient exceedances such as over-temperature and overspeed. It is currently limited to electric engines. Batteries and power distribution systems are outside its current scope.
The MOC-EHPS.420 document explicitly incorporates EUROCAE ED-321 as the primary guidance material for demonstrating endurance compliance, particularly focusing on the electrical engine component of EHPS, while excluding the battery and electrical power distribution from the current scope. It clearly acknowledges that, in hybrid systems, already certified turbines, piston engines, or APUs can leverage credit from their type certificates to satisfy part of the endurance substantiation. Additionally, the document establishes important regulatory linkages with CS-E paragraphs, recognising that the endurance philosophies applied to conventional combustion engines remain foundational for EHPS certification. Finally, the diagram on page 8 (Figure 1), originally published by EUROCAE effectively illustrates the relationships between EHPS.40, EHPS.440, EHPS.450, and EHPS.420, offering a clear visual summary of the endurance compliance framework.
EHPS.450 – Teardown Inspection
This stage follows endurance and durability testing, evaluating whether the EHPS remains safe and airworthy. It was developed to verify that the post-test conditions support continued operation and to identify wear mechanisms and degradation for maintenance planning.
Using functionality checks, non-destructive inspections and component disassembly assessments, the results can define inspection, replacement and repair intervals as per the ICA (Instructions for Continued Airworthiness).
Following endurance and durability testing, each EHPS must undergo a strip inspection to verify that its condition supports safe continued operation, with functional checks performed beforehand to ensure all components operate normally. Any adjustable or independently set components must retain their initial settings within acceptable limits, and if the teardown reveals the need for part replacement, further testing may be required, as determined by EASA.
The MOC-EHPS.450 document explicitly references key industry standards, notably EUROCAE ED-321, which provides the detailed guidance and methodology for teardown inspections following endurance testing, including specific checks for electric propulsion systems based on identified wear mechanisms. Additionally, the document integrates IEC 60270 (High Voltage partial discharge measurements) and IEEE 43 (testing insulation resistance of electric machinery) as part of the non-destructive evaluation techniques used to assess electrical component degradation. Together, these references confirm that the proposed Means of Compliance (MOC) are firmly anchored in internationally recognised standards, ensuring a robust and industry-aligned approach to verifying EHPS post-test integrity and continued airworthiness.
Calibration Assurance
The MOC-EHPS.440 document specifically acknowledges that for hybrid systems incorporating already certified turbines, piston engines, or APUs, credit can be taken from the performance, limitations, and installation procedures established in their type certificates (Section 4.1.3). This approach reduces redundancy and streamlines the calibration assurance process within EHPS certification. Additionally, the document references EUROCAE ED-321 as a key guidance standard, particularly for defining calibration test sequences, pass/fail criteria, and data analysis requirements related to endurance testing. Including these references ensures that applicants understand both the available certification credits and the detailed compliance methodologies provided by established international standards.
The EHPS must be subjected to calibration tests that are necessary to establish its power characteristics and the conditions both before and after the endurance and durability demonstrations specified in Subpart D of the SC E-19, specifically, EHPS.420 and EHPS.450 as seen above and EHPS.430 which is a durability test that validates that all EHPS parts can withstand expected operating conditions over time, with low probability of failure between overhaul or replacement intervals. This combination forms a test-to-inspection validation chain.
EHPS.440
This section defines how to demonstrate compliance with EHPS.440 – Calibration Assurance as part of the EASA Special Condition (SC) E-19 for Electric/Hybrid Propulsion Systems (EHPS). It addresses the necessity to verify engine power characteristics and functional integrity before and after endurance and durability testing, particularly for electric propulsion architectures.
This EHPS applies to electric engines and hybrid configurations, including turbines, reciprocating engines and APUS. It focuses on engine-only components, while propulsion batteries and distribution systems are excluded.
It mandates calibration tests to establish engine power-output characteristics while detecting performance degradation during endurance and durability campaigns. It also provides diagnostic data on rotor speed ranges, vibration signatures and other operating parameters.
Recording must take place at sea-level conditions across the full performance envelope (up to the highest rating) for initial and final calibration curves. The calibration process also validates safe continued operation and informs future maintenance/airworthiness actions.
Safety Assessment
This document outlines how to meet the requirements of EHPS.80 – Safety Assessment under the EASA Special Condition SC E-19 for Electric/Hybrid Propulsion Systems (EHPS). It emphasises the necessity of a coordinated, system-level safety assessment that accounts for the unique integration of EHPS into modern aircraft, extending beyond traditional engine boundaries. It includes the well-known principle that the probability of a failure must be inversely proportionate to its consequences. It also includes the concept of critical parts (shown in EHPS.90 Critical parts).
EHPS.80
The MOC applies to electric reciprocating and turbine engines within EHPS architectures. Additionally, for newly developed systems and pre-certified components used within an EHPS context.
The key safety assessment principles for integration with aircraft safety objectives require the EHPS designs to allow the aircraft to meet the qualitative and quantitative safety goals of its certification basis (e.g., CS-23, CS-25, VTOL.2510). The assessments should also be interactive and performed in close collaboration with the aircraft manufacturer.
Information from an EASA/FAA study, found that engine loss of power (LOP) events in a single-engine aircraft can lead to a wide range of outcomes, including Hazardous and Catastrophic incidents, in particular during take-off or landing phases. This led to the following classification proposals at aircraft level.
Proposal 1 treats LOP as a "Major+" failure condition. This means it is more severe than a typical Major classification but does not reach the threshold of being Hazardous. Under this proposal, the assumption is that a loss of power introduces a significant increase in pilot workload and may require the pilot to rely on emergency procedures to safely recover the aircraft. This classification is applied consistently across all phases of flight, making it a conservative and broadly applicable safety position. It aligns with standards such as ASTM F3230-20 and FAA Special Conditions for electric engine control.
Proposal 2 classifies LOP as Major under most conditions but recognises that it may change to Hazardous or even Catastrophic during critical phases of flight, such as take-off or landing. This acknowledges that the consequences of power loss can vary dramatically depending on when it occurs. Proposal 2 encourages safety assessments that account for flight phase sensitivity and supports a more scenario-specific certification strategy.
Both proposals are intended to shape how EHPS developers design for fault tolerance and assess risks associated with power loss, but differ in how conservatively they define those risks across flight conditions. EASA has included a diagram which represents a potential way to proceed, especially when starting from an existing EHPS design.
The means of compliance for electric engines addresses the following topics: standards for the safety assessment process, critical parts, short circuits and electric arcs, single fault tolerance for electrical and electronic failures leading to LOP/LOT. These points are further described below.
To align with the above-mentioned proposals, the design expectations have been defined so that single electrical/electronic failures must not lead to LOPC/LOTC (loss of power/loss of thrust control). The EHPS.350 maintains this concept even if the fault tolerance is achieved at the system, rather than the engine level. Finally, the critical parts, such as the shafts and bearings, must meet strict reliability standards and should be designed out through redundancy.
To evaluate short-circuit and arc risks, a detailed analysis of short circuits, electric arcs and serial arcs must be carried out to avoid failures across multiple engines. The assessment must include Electromagnetic Interference (EMI) effects, fire hazards and continued rotation risks in permanent magnet (PM) electric machines.
For electric engines that cannot meet traditional single-fault tolerance, a new rating framework has been introduced, the single-fault ratings (SFR) concept. This includes 2 ratings:
These ratings define safe degraded modes and must be included in the engine’s operating manual and validated in certification testing.
The final results of the EHPS.80 safety assessment supports the analysis of fire protection, overspeed containment, and power system protection.
At Murzilli Consulting, we recognise that the evolving regulatory landscape around EHPS demands technical excellence and strategic foresight. The latest proposed Level 2 Means of Compliance (MoC) to SC E-19, which covers Overspeed and Containment Demonstration, Endurance and Durability Demonstration (A), Calibration Assurance, and Safety Assessment, highlights a critical shift towards more robust, performance-driven certification frameworks. These updates are pivotal for innovators in the advanced air mobility (AAM) space seeking timely, safe, and scalable paths to market.
The means of compliance for reciprocating engines and turbine engines is the reference to the safety analysis paragraphs of the CS-E: CS-E210 for reciprocating engines and CS-E 510 for turbine engines.
With our expertise and hands-on experience in regulatory and technology certification strategy, Murzilli Consulting is uniquely positioned to guide Original Equipment Manufacturers (OEMs), system integrators, and developers through this transition. Whether it's interpreting EASA’s requirements, developing compliance roadmaps, or supporting MoC development and validation, we offer full-spectrum advisory services to turn regulatory complexity into a competitive advantage.
Would you like to know more about our support services for EHPS or any of our other customised services? Write to us for more information or to book an initial consultation.
