Based on the initial operational, infrastructure and interoperability requirements, as well as the initial functional requirements, a first set of technical specifications will be developed for the dedicated sandbox module and the associated procedure pack. A first solution-centric risk assessment will be developed and incorporated in the first version of the project and risk management plan foreseen in work package 5 (WP5). In parallel, work will start on the initial safety assessment report (SAR), the initial environmental assessment report (ENVAR) and the initial operational services and environment definition (OSED). This shall take into account technology which may support the integration of high-altitude platform systems (HAPS) (e.g. remotely piloted aircraft systems (RPAS) development, flexible use of airspace (FUA), dynamic mobile area (DMA) type 3, etc.), as well as the following elements:

• Performance of the HAPS
• Weather impact (especially during take-off, climb and descent phase)
• Network impact (effects on overall capacity)
• communications, navigation and surveillance (CNS) requirements (e.g. automatic dependent surveillance–broadcast (ADS-B), Mode N, separation)
• datalink infrastructure (datalink requirements, lost command and control link)
• Ground handling of HAPS on airports
• Handling of nominal and non-nominal behaviour, e.g. in-flight emergencies
• Compliance with existing applicable regulations, i.e. Annex 2 “Rules of the Air”

While the underlying ECHO concept of operations (CONOPS) corresponds to technology readiness level (TRL) 2, the development incorporates conceptual and technological elements from other projects (such as Obelisk in Germany) and as such the initial maturity level for Solution #2 is estimated to be TRL 3. It is however anticipated that the solution will mature quickly and therefore the first maturity gate is anticipated at TRL 5. All these elements will therefore serve for the development of the initial Solution #2 prototype/platform and associated procedure pack, to be used for the validation activities supporting the TRL 5 maturity gate check. For this, a validation plan will be produced that will address the main elements of the concept for the validation. The requirements for the validation will be defined and the validation itself will be described. Based on the validation plan the validation infrastructure will be prepared and necessary data collected.

In Solution #2, for the TRL 5 maturity gate check a real-time validation is foreseen, including a conflict resolution tool for HAPS based on artificial intelligence (AI). This simulation may be integrated with the similar one in WP3 looking at procedural and technical aspects integrating network and local levels of the developed solution (like technical interoperability and contingency procedure alignment), but also attempting to maximise synergies and minimise costs. A validation report will be produced on the basis of data which were collected during the validation trials, to be included in the TRL 5 maturity gate data pack.

Once the initial OSED is available, an interim cost-benefit analysis (CBA) will be conducted. The costs of the different stakeholders (e.g. HAPS manufacturer/operator and air navigation service provider (ANSP)) will be taken into account.

Also based on the initial OSED and other elements of the initial operational and functional requirements assessment (initial SAR, initial ENVAR), the development of the full Solution #2 safety and performance requirements – operational services and environment definition/interoperability (SPR-OSED/INTEROP) will start. Taking into account initial design elements as well as the result of the TRL 5 validation, the full SPR-OSED/INTEROP will be used to prepare the TRL 6 validation, for which the technical requirements for the Solution #2 sandbox module and associated procedure pack will be updated as well. Together with the updated Solution #2 prototype/platform and procedure pack and the updated validation plan, this will set the scene for the validation exercises in support of the TRL 6 maturity gate.

Flight trials shall be conducted by Airbus (Zephyr) and Skydweller to validate the OSED (validation level 2). Therefore, a coordination with the authorities in the affected countries must be established. As for the TRL 5 maturity gate validation, it is envisaged to integrate at least some parts of this validation with the exercises in WP3.

During the last part of the project, the full Solution #2 contextual note, the standardisation requirements and compliance assessment (STAND), the regulatory requirements and compliance assessment (REG), as well as the final CBA, will also be developed. This will enable the provision of a full Solution #2 data pack in support of the TRL 6 maturity gate, as per the SESAR management handbook.