On May 28, 2026, TÜV Rheinland updated its technical specification for eVTOL battery certification (RTS-eVTOL-Battery V3.2), introducing a mandatory Thermal Propagation Stoppage (TSP) test for all eVTOL battery systems seeking CE+UKCA dual marking. This change takes effect September 1, 2026, and raises the bar for thermal safety validation—impacting battery developers, system integrators, and airworthiness applicants in the advanced air mobility (AAM) sector.

Event Overview

On May 28, 2026, TÜV Rheinland published Revision 3.2 of its RTS-eVTOL-Battery technical specification. Effective September 1, 2026, the update mandates that all eVTOL battery systems applying for CE+UKCA dual conformity marking must pass a new Thermal Propagation Stoppage (TSP) test. The TSP requirement stipulates that, following induced thermal runaway in a single cell, adjacent modules must exhibit temperature rise ≤100°C and no flame penetration. This test is stricter than existing standards UN 38.3 and UL 2580.

Impact on Specific Industry Segments

Battery System Integrators

System integrators assembling eVTOL battery packs are directly affected, as the TSP test evaluates module-level and pack-level thermal propagation behavior—not just cell-level safety. Compliance requires redesigning thermal barriers, spacing, cooling architecture, and fire containment features. Impact manifests in extended development timelines, higher BOM costs for certified thermal interface materials and encapsulants, and increased validation effort during type testing.

eVTOL Aircraft OEMs

OEMs relying on third-party battery systems face cascading certification dependencies. A non-compliant battery may delay aircraft-level type certification under EASA SC-VTOL or UK CAA CAP 722, as battery safety is a foundational element of airworthiness. OEMs must now verify TSP compliance early in supplier selection and incorporate TSP test reports into their safety cases and design assurance documentation.

Battery Cell Suppliers

While the TSP test is applied at the system level, cell suppliers influence outcomes through intrinsic thermal stability, vent gas composition, and energy density trade-offs. Cells with lower thermal runaway onset temperatures or higher exothermic reaction enthalpy increase the likelihood of propagation—even with robust system-level mitigation. Suppliers may see increased demand for data packages supporting TSP modeling (e.g., ARC calorimetry, vent gas analysis) and tighter specifications from integrators.

Certification Support & Testing Service Providers

Laboratories and engineering consultancies offering eVTOL battery certification support must now validate TSP test capability—including calibrated thermal runaway induction methods (e.g., nail penetration, heating wire), high-speed thermal imaging, and flame penetration detection per the RTS-eVTOL-Battery V3.2 protocol. Capacity constraints and lead times for TSP testing are expected to rise, particularly among labs not yet accredited for this specific scenario.

What Relevant Enterprises or Practitioners Should Focus On — And How to Respond

Monitor official implementation guidance from TÜV Rheinland

TÜV Rheinland has not yet published detailed test protocols, acceptance criteria definitions (e.g., ‘adjacent module’ boundary), or equivalency pathways for alternative test methods. Enterprises should subscribe to TÜV’s official notifications and attend upcoming technical webinars—especially before initiating formal application submissions after September 1, 2026.

Review current battery designs against TSP-specific failure modes

Before redesigning full systems, conduct internal TSP gap assessments: simulate single-cell thermal runaway using available cell data; evaluate heat transfer paths between modules; assess flame barrier integrity under realistic venting pressure and gas composition. Prioritize modules with highest inter-module thermal coupling or shared cooling channels.

Engage with TÜV Rheinland early on pre-assessment or feasibility studies

Formal TSP testing is resource-intensive. Companies preparing for certification in late 2026 or 2027 should request pre-submission reviews or feasibility studies from TÜV Rheinland. These engagements help clarify interpretation of V3.2 requirements, identify likely non-conformities early, and align test planning with project milestones.

Update procurement and supply chain agreements to reflect TSP accountability

Contracts with cell suppliers and module manufacturers should explicitly assign responsibility for TSP-relevant parameters (e.g., maximum allowable vent gas temperature, minimum thermal resistance of module housings). Include clauses requiring sharing of validated thermal data and granting access for joint TSP test witnessing.

Editorial Perspective / Industry Observation

Observably, this update signals a shift from component-level safety compliance toward integrated system-level hazard containment—a reflection of regulators’ growing emphasis on fault tolerance in AAM platforms. Analysis shows the TSP requirement does not yet appear in EASA’s latest AMC 20-28 or UK CAA’s CAP 722 Annex G, meaning it remains a certification body–specific condition, not a regulatory mandate. However, given TÜV Rheinland’s role in CE+UKCA marking—and the de facto influence of leading Notified Bodies on industry practice—it is more appropriately understood as an emerging de facto benchmark. The timing (2026 implementation) suggests alignment with anticipated first commercial eVTOL type certifications, making it a near-term operational signal rather than a distant policy horizon.

Conclusion
This update marks a concrete step toward harmonizing battery safety expectations across the CE and UKCA frameworks for eVTOL applications. It does not introduce new regulatory law, but it materially raises the technical and procedural bar for market access in key jurisdictions. For stakeholders, it is best understood not as a standalone compliance checkpoint—but as an indicator of tightening system-level safety expectations across the AAM certification ecosystem. Proactive alignment with TSP requirements now reduces risk of rework, delays, and scope creep later in certification programs.

Information Source
Main source: TÜV Rheinland official announcement and RTS-eVTOL-Battery V3.2 specification document (published May 28, 2026).
Note: Details on test methodology, laboratory accreditation requirements, and potential transitional arrangements remain pending and require ongoing observation.