What is your Type? EASA announces the final Means of Compliance for M2 Mitigations for Medium Robustness, reducing GRC by 1 point

On July 6th, 2023, the EASA – European Union Aviation Safety Agency published the Means of Compliance with Light-UAS 2512 / Means of Compliance with Joint Authorities for Rulemaking on Unmanned Systems (JARUS) #SORA M2 for Medium Robustness.

This Means of Compliance was created and addressed “to UAS operators, UAS manufacturers, and mitigation means manufacturers (typically but not only: parachute recovery systems)“.

This Means of Compliance for M2 Mitigation (henceforth, referenced as “M2 MOC” in this article) applies to all SAILs and is intended for:

➢ Operators who are not designers of the UAS or of the mitigation means: they apply to the NAA for OA;

➢ Operators who have also designed the UAS and/or the mitigation means: they may apply to the NAA for OA or to EASA for DV; and

➢ Designers who have designed the UAS and/or the mitigation means and do not operate the UAS: they apply to EASA for DV.

Article Structure:

In this article, we provide the reader with the following information:

• Background information about the M2 MOC for Medium Robustness;
• An M2 MOC summary;
• Key snippets from the three chapters of the M2 MOC; and
• Opinions of the M2 MOC from AVSS – Aerial Vehicle Safety Solutions Inc. | Drone Parachute Recovery & Guided Delivery Systems.

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Background:

• In June 2022, EASA developed an initial M2 MOC proposal for Medium Robustness.
• Stakeholders were quite active in providing feedback and comments to EASA.
• EASA created a UAS Technical Body (TeB) working group in the fall of 2022 to address the specific technical (e.g., Parachute Recovery Systems) requirements to achieve Medium Robustness.
• In February 2023, EASA hosted an industry workshop in Cologne, Germany to provide stakeholders with an opportunity to review, discuss, debate, and collaborate on the proposed M2 MOC.
• From February 2023 to March 2023, stakeholders were provided the opportunity to submit written comments to EASA.
• EASA collected feedback through the Comments Response Document (CRD), which is “the feedback received during the Consultation phase (or Notice of Proposed Amendment phase) of the Rulemaking Procedure. They provide explanatory notes on the Consultation phase, and provide the Agency’s response to this feedback”.
• Per the published CRD, it appears that 188 comments were submitted by 17 stakeholders. Of these 188 comments, 57 were “accepted”; 55 were “rejected”; 33 were “noted”; 27 were “partially accepted”; 12 were “acknowledged”; and 4 were “thank you” (more on this below).
• The CRD comments were from regulators (e.g., Federal Office of Civil Aviation Switzerland, Swedish Transport Agency), drone and component manufacturers (e.g., Schiebel, Wing, RigiTech, Airbus Helicopters, AVSS – Aerial Vehicle Safety Solutions Inc. | Drone Parachute Recovery & Guided Delivery Systems), and other groups (e.g., end users, service providers, and industry associations).

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M2 MOC Summary:

The M2 MOC is organized into three chapters.

• Chapter 1: Clarifying nominal integrity target for medium robustness to decrease Ground Risk Class (GRC) by 1 point.
• Chapter 2: The M2 MOC “Types”, which are categorized under Type 1, Type 2, and Type 3 (more on this below).
• Chapter 3: Several examples of how to apply for the M2 MOC. EASA stated that “compliance with these examples can be declared in the frame of a request for operational authorization, making available for the NAA the identified evidence of compliance” (Page 2).

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Chapter 1 Summary:

M2 mitigations are intended to reduce the ground impact once the control of operations is lost.

Reducing the ground impact can be achieved by reducing the critical area (Type 1), the lethality (Type 2), or a hybrid of Type 1 and Type 2 (Type 3):

• Type 1: The objective is to reduce the expected Critical Area of the impact. Critical Area is defined as “the sum of all areas on the ground where a person standing is expected to be impacted by the UA system during or after a loss of control event” (Page 10, EASA’s MoC on M2 medium Robustness, 22.02.2023);
• Type 2: The objective is to reduce the lethality of causing a fatal injury. If lethality ≤ 0.1 (i.e., 10%), then 1 point can be reduced from GRC; and
• Type 3: This is a hybrid of Type 1 and Type 2 where the critical area and lethality are reduced [lethality * CAc/CAn ≤ 0.1].

Chapter 2 Summary:

The M2 MOC specifies the requirement of supporting evidence and documentation that needs to be submitted to a National Aviation Authority. This includes proof that the mitigation means (1) reduces the effect of ground impact, (2) works with sufficient reliability in the event of a loss of control, and (3) does not increase risk. Applicants will need to declare that they achieve all three claims.

With M2 medium integrity, there is an assumption that impact dynamics and post-impact hazards are significantly reduced; however, they assume that a fatality may still occur.

Type 1 can be substantiated by analysis or test that the “critical area after the application of the mitigation means is lower than or equal to the CAn of the adjacent column to the left of the one selected initially in step#2 of SORA” (Page 8).

Type 2 can be substantiated by “(i) ASTM F3389/F3389M-21 methodologies could be proposed where it is possible to adapt the thresholds to reach 90% reduction; (ii) Demonstrate that an impact with a person in the most critical condition results at most in 30% probability of AIS3+ injuries; (iii) Ensure a maximum impact energy of less than 175 J; or (iv) Ensure a maximum transferred energy of less than 80 J in an impact with a person” (Page 8).

Type 3 is demonstrated by determining an approximate percentage of the global risk reduction of the critical area and reduction of lethality.

Additional relevant information includes:

• (1) ASTM F3322-18 parachute standard is an acceptable MOC (Example # 1 in Chapter 3);
• (2) Applicants will need to list all probable malfunctions that may cause the crash of the UA;
• (3) Two flight tests and 30 ground activations of the PRS have been deemed acceptable for some of the Parachute Recovery System examples (more on this below);
• (4) A failure during the testing must be documented and include a root cause, corrective action, and a restart of the testing documentation, which means no cherry-picking; and
• (5) Flight testing must be “conducted with a configuration representative of the operation in flight and they need to exercise all the chain of elements” (Page 10), which means that altering the drone’s Centre of Gravity or using a code base with a tighter Automatic Triggering System (ATS) threshold is not allowed, same as the ASTM F3322 requirements.

Chapter 3 Summary:

Chapter 3 includes four examples, three of which use a Parachute Recovery System for compliance:

Example # 1: ASTM-compliant Parachute Recovery System (PRS) for sUAS (Type 2 & Type 3)

• Applicable for UAS in 1m and 3m size categories at or below 25kg MTOM.
• ASTM F3322 − 18 compliant parachute recovery system installed on UAS.
• Parachute descent rate and wind speed limitation combine to a speed vector of less or equal to 10 m/s.

Example # 2: Parachute Recovery System (PRS) for sUAS (type 2 & 3)

• Applicable for UAS in 1m and 3m size categories at or below 25kg MTOM.
• Parachute recovery system installed on sUAS.
• Parachute descent rate and windspeed limitation combine to a speed vector of less or equal to 10 m/s.

Example # 3: Parachute Recovery System (PRS) for large UAS (type 1)

• Applicable for UAS in 8m and larger size categories.
• Parachute Recovery System installed on large UAS.
• Parachute descent speed less or equal to 8 m/s.

Example # 4: UA maximum impact energy of less than 175 Joules (type 2)

• The mitigation is linked to the inherent UAS characteristics showing a less lethal impact kinetic energy.

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AVSS’s Opinion of M2 MOC:

The M2 MOC for Medium Robustness by EASA is a step in the right direction. The M2 MOC provides clarity and predictability for stakeholders designing for Medium Robustness. Similar to the regulations in Canada under Transport Canada – Transports Canada for the Advanced Category for Operations Over People, Medium Robustness is achievable with a Parachute Recovery System. As well, the M2 MOC acknowledges that the use of an ASTM F3322 Parachute Recovery System is an appropriate path; however, not the only path to compliance. Note, although ASTM F3322-18 testing is expensive due to the nature of the 45 failure scenarios, AVSS believes that this standard should be the default for commercial drone companies that have global aspirations and that want to ensure that their customers are also compliant High Robustness in Europe, approvals of their SFOCs in Canada, and positioned for the Federal Aviation Administration Operations Over People under Category 2 and Category 3 in the USA. This is especially the case where the EASA respondent to the CRD has stated “Keep in mind that ASTM F3322 is generally more suitable for M2 High which is to be design verified by EASA”.

From the proposed M2 MOC in February to the final M2 MOC, EASA has improved the overall process and added clarity for stakeholders. Some items that were addressed include:

1. Clarifying language that the M2 mitigation “does not increase risk” whereas the previous language stated, “does not introduce additional risk” (Page 6). This may appear as a small item/typo, but the potential negative effect would be great as the net benefit of an M2 mitigation is the focus;
2. Identifying that there are Type 1 situations where Unguided Parachute Recovery Systems (i.e., Passive) may drift in the wind after deployment and increase the target critical area of a drone that is no longer under control. To address the shortcomings of these passive systems, EASA has stated that “(i) for parachutes or systems that will drift in the wind, the maximum wind to be considered as operational limitation is the one which, excluding gusts, would still allow achievement of target critical area [and] (ii) for non-drift systems, such as impact, glide or ballistic mitigations, the maximum wind to be considered as operational limitation is the one which, excluding gusts, would still allow achievement of target critical area analysis or testing…”(Page 8); and
3. In Examples # 1 and # 2 in Chapter 3, EASA has also updated the language to include the reality of how crosswinds need to be included when a parachute is deployed. They specifically state that the “Parachute descent rate and windspeed limitation combine to a speed vector of less or equal to 10 m/s” (Page 13 & Page 15). In several countries, this windspeed variable is not included. Some regulators only use the vertical descent speed, which is misleading when considering the transfer of energy potential on the horizontal axis and the injuries that a bystander may experience.

While the M2 MOC is an improvement for the industry, there are items that could be adopted to improve the overall safety of commercial drone operations. First, it is the opinion of AVSS that the use of a Guided Parachute Recovery System should be valid for Type 1 (critical area) and Type 2 (lethality reduction). Per the comments in the CRD by the EASA respondent, Type 1 appears to be the initial interpreted use case where the “activation of a guided (aka controlled) parachute is not a loss of control of operation in the first place… and guided parachutes can be used to minimize critical area, if the applicant can provide evidence that this heading into the wind functionality works in all probable failure cases”.

Finally, there are a few items that seem to be a bit “light” on requirements and testing that may require additional scrutiny in the near future include:

1. Only two representative flight tests with 30 ground activations are deemed sufficient for some examples with the use of a Parachute Recovery System. Several commenters with Parachute Recovery System testing experience critiqued this approach as such few flight tests do not fully account for the randomness of a parachute deployment, the proper calculation of Minimum Deployment Altitude, and the safety factor demonstrated from shock load testing (remember, the ASTM F3322-18 requires 45 successful tests);
2. Several CRD submissions attempted to inform the EASA comment reviewers of the current shortcomings of the ASTM F3322-18 test. For example, commenters stated the need for adapting the MDA calculation for hover and full-forward (this is important for those using a winch for drone delivery). Unfortunately, the reviewers adopted the ASTM F3322-18 standard without acknowledging that there is a revised ASTM F3322-22 and that the standard is expected to be updated to ASTM F3322-23; and
3. There were several comments regarding Third Party Testing Agencies (TPTA), which oversee Parachute Recovery System testing. For example, one commenter stated that they “would like to ask for clarification on the third‐party testing agency (TPTA): could this correspond to the concept of notified body/conformity assessment body as per Delegated Regulation (EU) 2019/945”. EASA has chosen to use the unaltered ASTM F3322-18 document and not clarify who/what is a TPTA. This situation has come under scrutiny in the past by regulators and, hopefully, future iterations of the M2 MOC will address this topic.

Final Thoughts:

With January 1st, 2024 around the corner, EASA has taken a timely and appropriate step in publishing the M2 MOC for the European commercial drone market. This Means of Compliance for Medium Robustness may not be the only method to receive a 1-point reduction in GRC; however, it covers a practical approach. As the industry continues to grow and add economic and societal benefits, we look forward to the M2 MOC adoption by National Aviation Authorities and the future release of an M2 MOC for High Robustness.