domain: spi phys

text:
Federico Trovarelli

Giuseppe Guidotti
email: giuseppe.guidotti@deimos-space.com

Giovanni Medici

Thorn Schleutker

Burkard Esser

Ingrid Monika Dietlein

Giovanni Gambacciani

Giuseppe Governale

Jean-Luc Verant

Yann Dauvois

J.-L Verant

Y Prevereaud

Advanced European Re-Entry System Based on Inflatable Heat Shields EFESTO project overview: system and mission design and technology roadmap

Keywords: Reusability, Mars Exploration, EDL, Flexible-TPS, Inflatable Structure, Aerodynamic Decelerators

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

The European Union H2020 EFESTO project is coordinated by DEIMOS Space with the end goals of improving the European TRL of Inflatable Heat Shields for re-entry vehicles from 3 to 4/5 and paving the way to further improvements to be implemented in a possible future IOD to achieve TRL 6, eventually in agreement with ongoing and future European efforts in this context [START_REF] Dillman | Planned Orbital Flight Test of a 6m HIAD[END_REF]. The project includes design and ground test activities, covering the key subsystems of inflatable structure and Flexible-Thermal Protection System (F-TPS) that compose a Hypersonic Inflatable Aerodynamic Decelerator (HIAD).

This paper provides an overview of the project, the outcomes of the detailed design of atmospheric entry mission scenarios and an overview of the technology roadmap together with the aerothermal and structural test campaigns, consolidating and extending the results already presented in [START_REF] Bonetti | Advanced European Re-Entry System Based on Inflatable Heat Shields Detailed Design (EFESTO project)[END_REF]. In particular, the recovery of reusable small launcher upper stages and a high-mass Mars robotic exploration EDL mission have been selected as testbeds for the characterization of the performance that HIAD systems shall guarantee.

For the Earth Application, the recovery of the AVUM VEGA upper stage has been chosen as baseline case study. The current mission layout consists of a deorbit from Polar Orbit followed by a controlled entry phase. Atmospheric deceleration is achieved using a 4.5m diameter class HIAD followed by a parachute descent phase. Finally, a parafoil shall enable Mid-Air-Retrieval (MAR) of the entry vehicle with a helicopter. The Mars robotic exploration mission design resulted in a 9m diameter HIAD class, combined with Supersonic Retro-Propulsion (SRP) for safely landing the 2.5 tons payload at MOLA +3km target altitude.

The AVUM recovery entry mission analysis confirmed the HIAD as an appealing, performing and robust solution for the purpose of safely returning this VEGA upper stage to a targeted recovery area. For the Mars application mission analysis showed that, compared to state-of-the-art technology, the implementation of the HIAD efficiently provides larger drag during the entry phase, thus allowing to increase both landed mass and MOLA altitude at which a soft landing is possible.

VEGA AVUM stage recovery mission EDL

After injecting its payload into the target orbit, the AVUM VEGA upper stage performs a deorbiting manoeuvre and, not being protected by any TPS, it burns up in the Earth's atmosphere, eventually demising in a safe area for ground population. In any case, this valuable hardware is currently lost at the end of each VEGA launch.

The first key aspect considered in EFESTO to make this stage reusable is the need to protect the AVUM with a HIAD from the harsh entry environment. A feasible trajectory shall comply with a set of applicable constraints and in particular those limiting the thermomechanical loads during entry.

The second aspect considered is the possibility of recovering the AVUM at the end of the re-entry flight with limited operational effort. The launch costs cut by reusing this hardware shall in fact outweigh the cost of recovery. A preliminary business case analysis has shown that the latter should not exceed the 10% of the value of the recovered hardware. For the AVUM case the most cost-efficient option consists of exploiting helicopters for MAR operations.

The reference EFESTO Earth full mission layout in Fig. 1 starts with the VEGA launch and injection of the payload into the target orbit (1), followed by the deorbiting manoeuvre and the separation of the payload adapter [START_REF] Bonetti | Advanced European Re-Entry System Based on Inflatable Heat Shields Detailed Design (EFESTO project)[END_REF]. At this point the HIAD is inflated and a controlled lifting entry phase starts [START_REF]Vega User's Manual Issue 4 Revision 0, Arianespace[END_REF]. The Centre of Gravity (CoG) of the HIAD is offsetted so that the vehicle is able to generate the necessary lift to be used for steering the flight trajectory. The entry phase ends at around Mach 1.6 when the pilot chute is ejected to extract a drogue parachute that further decelerates the payload (4). A parafoil deployed at low subsonic conditions guides the vehicle to the targeted MAR area [START_REF] Annaloro | Space debris atmospheric entry prediction with spacecraft-oriented tools[END_REF]. The final step is the necessary refurbishment of the recovered stage [START_REF] Refloch | CEDRE Software[END_REF] to prepare it for the following flight.

Entry vehicle system configuration

The HIAD shield shall enable the AVUM recovery without modifying the existing VEGA launcher subsystems distribution as defined in the User Manual [START_REF]Vega User's Manual Issue 4 Revision 0, Arianespace[END_REF]. The solution envisioned consists of storing it within the available volume under the VESPA.

The resulting system configuration is given in Fig. 2. The inflatable structure consists of two integrated volumes pressurized using a cold gas generator. The annular torus has a tear-shaped cross section and an outer diameter of 4.8m while the secondary conical volume covers the lateral surface area of the cone, that has a total height of 2.1m and an opening angle of 120°. The spherical rigid TPS nose measures 1.3m in radius. The resulting reference surface of the vehicle in entry configuration is around 18 m². Fig. 2: Earth scenario HIAD entry vehicle.

Entry vehicle aerothermodynamics

The aerodynamic coefficients of the vehicle have been defined for a lifting entry trajectory flown at a nominal Angle of Attack (AoA) of -15°. The initial AErodynamic DataBase (AEDB) was generated for selected trajectory points using the engineering code ARES, based on the FAST aerodynamics and aerothermodynamics solver [START_REF] Prévereaud | Contribution à la modélisation de la rentrée atmosphérique des débris spatiaux[END_REF][START_REF] Annaloro | Space debris atmospheric entry prediction with spacecraft-oriented tools[END_REF], that guarantees minimal computational effort. The computation was later refined taking advantage of CEDRE (Calcul d'Écoulements Diphasiques Réactifs pour l'Énergétique) Computational Fluid Dynamics (CFD) tool [START_REF] Refloch | CEDRE Software[END_REF] which provides an estimation of the coefficients for a wider range of Mach numbers (2 to 25) and AoA (-30° to +30°). Fig. 3 summarizes the values of the aerodynamic force coefficients generated by the vehicle flying at the nominal AoA as a function of the Mach number. It also shows the uncertainties due to discrepancies between the ARES and the CEDRE results and between the latter and flight data derived from the similar Apollo AS202 mission case.

It has to be noticed that the ARES solutions do not take into account turbulence and radiation heat transfer effects that might have a significant impact on the value of the wall heat flux, the latter depending on both re-entry conditions and vehicle size. In order to evaluate viscous and heat transfer contributions, CEDRE solver was used. In the computation a fully turbulent flow triggered at Mach 22.6 trajectory point, corresponding to maximum stagnation heat load from preliminary trajectory propagation, has been assumed. The F-TPS is threated as a super-catalytic wall that provides the highest atomic recombination process model and best matches the expected properties of the F-TPS material. Finally, it was assumed radiative equilibrium with a material total emissivity of 0.8 to account for the radiative cooling mechanism. The radiative heat transfer process has been estimated as being not a predominant heat transfer mechanism for the specific mission conditions. The simulation results indicated that the peak heating conditions are reached at the stagnation point. In here the heat flux equals 425 kW/m², while it varies from 230 kW/m² to 380 kW/m² on the windward surface of the cone and between 160 kW/m² and 400 kW/m² on its leeside. The analysis also confirmed stagnating flow, corresponding to extremely low heat flux values, in the AVUM payload rear zone of the vehicle.

EDL mission analysis

Fig. 5 shows the consolidated 2D Local Entry Corridor (LEC) that was defined for the vehicle described in the previous sections and assuming an Entry Interface Point (EIP) velocity of 7.6 km/s and parachute deployment at Mach 1.6. In this plot each curve is an isoline corresponding to either simple indicators, used in this case for relating the mission analysis with the thermal test campaign and the F-TPS design process, or active constraints not to be violated. The grey region contains the envelope, defined in terms of Ballistic Coefficient (BC) and flight-path-angle at EIP, that fulfils all imposed constraints. LEC is part of Deimos proprietary PETBOX atmospheric flight analysis tool [START_REF] Bonetti | PETbox: Flight qualified tools for atmospheric flight[END_REF].

The LEC analysis has shown that the entry corridor is limited by landing accuracy on the shallow side and by the maximum tolerable load factor and the maximum tolerable heat flux at the F-TPS cone for higher BC values on the steep side. For the reference vehicle layout, with an entry mass of 1096.61 kg corresponding to a BC of 46 kg/m², the entry corridor is 1.8º wide, ranging from -3.79º to -1.97º. The poor landing accuracy achieved by a pure ballistic HIAD entry, not complying with the recovery mission requirements due to a wide range of dispersions at EIP, suggested the need for a controlled lifting reentry. As already mentioned, the offsetting of the CoG allowed to obtain a trim AoA, ranging between -10º and -20º, so that the HIAD can generate lift. The resulting range capability can be used for compensating dispersions by controlling the bank angle during entry flight.

Fig. 6 demonstrates that for a -15º AoA trim angle a theoretical range capability between 300 and 400 km, corresponding to a compensation of about 150 to 200 km in the EIP position error, can be achieved. The results of the Monte Carlo campaign in Fig. 7 further confirmed that the chosen F-TPS sizing heat flux and aerothermal Arcjet test conditions are in line with the expected variability of atmospheric conditions during flight and perturbations in system mass and aerodynamic properties. Also, the same analysis demonstrated the compatibility of the achievable position accuracy at the end of the descent phase with the approximate 200km radius of the MAR area.

Mars robotic exploration EDL mission

The selected high-mass Mars exploration robotic baseline EDL mission is compatible with a launch in the 2030-2040 timeframe. Following an interplanetary transfer, the vehicle will perform a direct entry at hyperbolic arrival velocity in the Mars atmosphere. As depicted in Fig. 8, the first events consist of the cruise stage separation (1) followed by the separation of the bag protecting the stowed HIAD (2). After it gets inflated (3), the hypersonic re-entry phase starts. The HIAD provides aerodynamic deceleration until, after front shield ejection (4), it gets released [START_REF] Annaloro | Space debris atmospheric entry prediction with spacecraft-oriented tools[END_REF]. Touchdown speed is achieved using SRP down to ground [START_REF] Refloch | CEDRE Software[END_REF], and finally a Skycranelike system lowers the payload down to the surface [START_REF] Bonetti | PETbox: Flight qualified tools for atmospheric flight[END_REF].

System synthesis

The EFESTO Mars entry vehicle given in Fig. 9 houses a 2.5t scientific payload in a 2.8m x 2.5m envelope. The carrier frame in blue is equipped with the supersonic SRP system consisting of the fuel and helium tanks, avionics and the Skycrane-like equipment used to lower the scientific payload to the Mars surface. The SRP is a ring of multiple monopropellant Aerojet Rocketdyne MR-80B3100 thrusters that can be activated at Mach 2.3 and used down to hovering [START_REF]Space Propulsion Data Sheets, Monopropellant and Bipropellant Engines[END_REF], where the touchdown manoeuvre is performed. The thrusters could additionally be used for compensating any CoG displacement or other perturbances during part of the EDL flight. The basic architecture of the HIAD is similar to that designed for the AVUM recovery on Earth. It features an annular torus defining an outer diameter of the inflated cone of 8.8m and a secondary conical volume. With a total height of 2.6m, the opening angle of the cone measures 140°. The nose radius is 1.75m. The resulting reference surface of the vehicle in entry configuration in the order of 60m².

The interface between the HIAD and the rigid nose is integrated in the carrier frame. The HIAD is assumed to be pressurized using helium, already required for the pressurization of the fuel tanks. Alongside the rigid nose, heat protection is ensured by a properly dimensioned F-TPS and a flexible back cover complemented by an MLI layer on the back surface of the carrier frame.

Aerothermodynamics

As for the Earth mission, also for the Mars case the AEDB was preliminarily estimated at specific points of the reference ballistic entry trajectory using the ARES tool and later validated and extended with a dedicated CEDRE CFD campaign. Fig. 10 gives the estimated axial aerodynamic force coefficient of the entry vehicle, the others being null at AoA 0°. The numerical procedure to assess heating loads on the Mars HIAD entry vehicle, follows the same analysis path already described for the Earth mission. In particular, the assumptions already discussed regarding the super-catalytic wall, the radiative cooling and the shock layer radiative heat transfer process in combination with turbulence effect, still hold. The atmosphere, however, is assumed to be 100% CO2. Fig. 11 gives the temperature distribution obtained from the aerothermodynamic simulation under these assumptions for the Mars entry vehicle flying at Mach 25 and AoA 0°.

The results of the CFD campaign show that the local conditions of the Mars entry trajectory, in combination with the large size of the vehicle, trigger a laminar-toturbulent transition mechanism at around the junction between the sphere and the cone. The result is that the heat flux increases along the frontshield with respect to the stagnation point conditions so that, contrarily to the Earth mission case, the peak heating conditions are experienced on the surface of the HIAD cone. In particular, the heat flux at the stagnation point is equal to 289 kW/m², while on the cone it reaches 458 kW/m². On the back shield, as expected, the stagnating flux guarantees low heat flux between 7 kW/m 2 and 11 kW/m². Finally, due to high temperature CO2/CO and N2 atmospheric mixture species, infrared radiative overheating is a Martian entry environment specificity to be accounted for. The calculation of this contribution resulted in additional 30 kW/m 2 experienced at the frontshield.

Mission analysis

Fig. 12 shows the consolidated LEC that was defined for the vehicle described above, assuming an EIP velocity of 6 km/s and HIAD release at Mach 2.3. For the Mars EDL mission, the entry corridor is limited by the landing accuracy limit on the shallow size and by the maximum tolerable heat flux at the F-TPS cone on the steep side. The compliance with the landing accuracy can already be guaranteed by a ballistic entry and no controlled lifting re-entry is necessary. For the reference vehicle layout, with an entry mass of 6024kg corresponding to a BC of 62 kg/m², the entry corridor is 1º wide, ranging from -12.5º to -11.5º, suggesting a much steeper trajectory with respect to the Earth case, as expected as a result of the lower atmospheric density.

The additional 30 kW/m² due to the radiative component raise the expected maximum heat flux on the HIAD cone to 561 kW/m². This value, however, is still in line with the F-TPS sizing heat flux of 590 kW/m². The results of the Monte Carlo campaign in Fig. 13 further confirm that the chosen F-TPS sizing heat flux and aerothermal Arcjet test conditions are in line with the expected peak heat flux variability caused by variable atmospheric conditions during flight and perturbations in system mass and aerodynamic properties. The Monte Carlo campaign additionally proved that the SRP system is able to handle the perturbations and always achieves a soft landing within the required 50km landing accuracy requirement. The performance of the coupled HIAD and SRP deceleration in terms of fuel efficiency, however, revealed significant sensitivity to the atmospheric conditions encountered during the EDL flight.

The high versatility of the SRP system could theoretically allow to tune the EDL flight schedule, and in particular the location of the HIAD-SRP switch, with the objective of optimizing not only the mass that can be safely delivered but, eventually, also the MOLA altitude of the landing site. The sensitivity analysis that was carried out showed that anticipating the HIAD-SRP switch could make it possible to land a still relevant mass at higher MOLA elevation, while instead diving deeper with the HIAD into the atmosphere could significantly increase the landed mass. The former scenario would need an SRP system capable of operating at Mach larger than 2.3, while the latter would require that the vehicle in entry configuration, i.e., with the inflated HIAD, is stable at Mach numbers lower than 2, which is difficult to achieve for a typical Mars hypersonic entry vehicle shape.

EFESTO contribution to HIAD TRL increase

The preliminary and detailed design loops were followed by a ground effort aimed at investigating two key aspects of HIAD technology and raise the European TRL from 3 to 4/5. In particular, an extended aerothermal testing campaign was carried out for different F-TPS layups options and the mechanical properties of the inflatable structure where characterised using a relevant manufactured demonstrator. The details of these tests campaign are reported below.

Arcjet test campaign overview

The F-TPS is a foldable multi-layer structure consisting of an outer layer exposed to the external entry environment that has to withstand the highest temperature. It covers the inner layers that are meant to preventing the diffusion of heat to the internal structures and the payload. Within the EFESTO project several layups combination where designed and simulated, in agreement with HIAD system requirements. After a final screening, the three most promising F-TPS solutions, two for the Mars case and one for Earth, were subjected to thermal characterization tests in DLR's arc-heated facilities LBK, which allows comparative testing on sample basis at mission relevant conditions.

The LBK facilities consist of the two individual test legs, L2K and L3K. Both are particularly suited for thermal characterization and qualification of TPS materials and structures for atmospheric entry. The facilities allow for long-duration tests at flight relevant enthalpy conditions and within a realistic thermochemical environment.

The L2K facility can be used for tests in Martian atmosphere by using a mixture of 97% CO2 and 3% N2 as working gas. For thermal testing, samples and models are placed in the homogeneous hypersonic free stream. A comprehensive description of the LBK facility is given by Gülhan et al. [START_REF] Gülhan | Arc-Heated Facilities as a Tool to Study Aerothermodynamic Problems of Reentry vehicles[END_REF][START_REF] Gülhan | Mars Entry Simulation in the Arc heated Facility L2K[END_REF].

The test matrix included tests in two different configurations. The stagnation configuration is highlighted in Fig. 14. The setup is particularly useful for evaluating the principal capabilities of the F-TPS layups in a high-enthalpy environment. The conditions are defined by the gas atmosphere, the heat flux and the stagnation pressure. The corresponding sample holder was developed in a previous ESA study [START_REF] Johnstone | Investigating the Response of a Flexible TPS to a High Enthalpy Environment[END_REF] and could be re-used with minor modifications. On its front surface, the holder provides an open diameter of 45mm for the F-TPS sample. The layup can consist of several different layers of fabrics, insulation and gas barriers with a total thickness of up to 30mm. The test conditions were derived from the trajectory data of the respective applications in terms of heat flux, integral heat loads and stagnation pressure. During the tests campaign, main priority was given to the energetic parameters. Heat fluxes were varied up to the maximal entry flight heat flux predicted by the numerical simulations. The integral heat loads were set via the test duration. The heat load was also varied up to 150% of the predicted total heat load for demonstration purposes.

During all tests the F-TPS samples remained thermally stable. Post-test inspections did not indicate critical structural deficits, neither for the external fabric layers nor for the insulation layers. As illustrated by the photographs in Fig. 16, the exposed sample surfaces appeared uniformly heated in visual and infrared observations. Repetitive tests at identical test conditions showed a good reproducibility of the test results. All three F-TPS layups qualified for further consideration in the frame of the EFESTO applications. A second Arcjet test campaign is planned following the selection of the final layups, and will also include elements of the inflatable structure below the TPS, such as the F-TPS membrane.

IAD test campaign overview

The investigation of the mechanical behaviour of the inflatable structure as a sub-system was achieved through design, manufacturing and testing of a 2.4 m diameter demonstrator, scaled 1:2 with respect to the designed Earth case HIAD, in reference to already existing analogous test campaigns [START_REF] Swanson | Structural strap tension measurements of a 6 meter hypersonic inflatable aerodynamic decelerator under static and dynamic loading[END_REF]. The demonstrator, pictured in Fig. 17 and photographed in Fig. 18, is a highfidelity representation of the inflatable structure in terms of architecture, configuration, layout, and manufacturing solutions and additionally includes a fair-fidelity replica of the F-TPS and the outer mold-line of the AVUM stage. The focus of the testing campaign, executed in CIRA premises, was the verification of aspects related to stowing, folding, unfolding and inflation, followed by the verification of static strength under pressure pattern representative of re-entry conditions. Fig. 18. HIAD demonstrator after inflation testing.

For the purpose of replicating the pressure load during re-entry, the implementation of a vacuum-pool with a non-porous membrane, pictured in Fig. 19 was selected. This test set up additionally required the design and manufacture of a dedicated test rig. Also, the demonstrator was equipped with load-cells and a videofootage of the system behaviour was recorded during test sessions to be used for later computational reconstruction. The test campaign was successful and allowed not only to achieve verification of the HIAD structural integrity but also to increase the knowledge of HIAD behaviour and support both modelling and numerical correlations.

EFESTO technology roadmap

The European advancements in the inflatable aerodynamic decelerators technology can enable future space missions, allowing new scientific and technological achievements. These include the possibility of heavier payloads landed at higher elevations, resulting in an expansion of the planetary exploration boundaries, or, by integrating the HIAD in the launcher vehicle, the ability to the recover some of its main components.

To reach such operational capabilities, the EFESTO project is carrying out the technology development of the F-TPS and the inflatable structure. The test campaigns described earlier are filling the gap between the current state of the art and the TRL for a future IOD mission which is foreseen by the EFESTO technology roadmap.

The roadmap in Fig. 20 is built on a technology context activity, assessing past, present, and future missions linked to the EFESTO activity by technology category. The current international efforts and space missions' goals are in line with the development of a technology capable of enlarging our landing and reusability capabilities.

Enabling the exploration of Mars in regions not yet accessible is of most scientific interest for the possible existence of life and to support future human exploration and colonization. The objective of enhancing reusability of Earth orbiting spacecraft by means of a potentially lightweight alternative to rigid decelerators is in line with the principle of affordability and sustainability, which represent key factors for the current space industry.

Conclusions

EFESTO project allowed to develop and improve the European know-how in the field of HIAD systems with respect to system design and engineering, key technology design manufacturing and testing. To complete the investigation exercise on these peculiar systems further effort shall be put in place in the future in agreement with the technology roadmap introduced.

The results presented demonstrate that HIAD systems represent an enabling technology for the next class of high-mass Mars exploration missions and this technology can be key in reducing the cost of access to space through upper stage reusability. The need for advancing the European TRL of this technology, which is the primary objective of the EFESTO project, is thus confirmed and the relevance of an IOD mission that will enhance the European know-how in the field, of which the EFESTO consortium represents the core, is reinforced.

Fig. 1 .

 1 Fig. 1. VEGA AVUM recovery CONOPS.

Fig. 3 .

 3 Fig. 3. Earth HIAD axial force, tangential force and moment aerodynamic coefficients.

Fig. 4

 4 Fig. 4 gives the temperature distribution obtained from the aerothermodynamic simulation under these assumptions on the Mars entry vehicle flying at Mach 22.6 and AoA -15°.The simulation results indicated that the peak heating conditions are reached at the stagnation point. In here the heat flux equals 425 kW/m², while it varies from 230 kW/m² to 380 kW/m² on the windward surface of the cone and between 160 kW/m² and 400 kW/m² on its leeside. The analysis also confirmed stagnating flow, corresponding to extremely low heat flux values, in the AVUM payload rear zone of the vehicle.

Fig. 4 .

 4 Fig. 4. Temperature distribution on the Earth HIAD flying at Mach 22.6 and AoA -15°.

Fig. 5 .

 5 Fig. 5. Earth entry mission scenario 2D LEC.

Fig. 6 .

 6 Fig. 6. Range capability as a function of trim AoA.

Fig. 7 .

 7 Fig. 7. Earth entry mission scenario Monte Carlo heat flux verification.

Fig. 8 .

 8 Fig. 8. Mars HIAD robotic EDL mission CONOPS.

Fig. 9 .

 9 Fig. 9. Mars scenario HIAD entry vehicle.

Fig. 10 .

 10 Fig. 10. Mars HIAD axial aerodynamic force coefficient.

Fig. 11 .

 11 Fig. 11. Temperature distribution on the Mars HIAD flying at Mach 25 and AoA 0°.

Fig. 12 .

 12 Fig. 12. Mars entry mission scenario 2D LEC.

Fig. 13 .

 13 Fig. 13. Mars entry mission scenario Monte Carlo heat flux verification.

Fig. 14 .

 14 Fig. 14. Test environment for stagnation flow test.The tangential flow configuration in Fig.15is more representative for the considered application as compared to the stagnation setup. This is because of the aerothermodynamic loading, that also includes shear stresses induced by the tangential flow. A new construction for the interior of the sample holder had to be designed and manufactured. The realized design allows exposure of a square area with 80mm side length to the tangential flow field. The holder keeps the outmost fabric layers under tension during the tests.

Fig. 15 .

 15 Fig. 15. Test environment for tangential flow test.

Fig. 16 .

 16 Fig. 16. Sample appearance in stagnation test (left) and tangential flow test (right).

Fig. 17 .

 17 Fig. 17. HIAD demonstrator CAD model.

Fig. 19 .

 19 Fig. 19. HIAD demonstrator under static load testing.

Fig. 20 .

 20 Fig. 20. EFESTO technology roadmap.

Acknowledgements

This project has received funding from the European Union Horizon 2020 research and innovation programme under grant agreement No 821801. More information available at: https://cordis.europa.eu/project/id/821801

The EFESTO consortium acknowledges essential contributions from Thin Red Line Aerospace and ALI Scarl Italia concerning the IAD Demonstrator design, manufacturing, integration and testing processes.


Diane Fromage

Democratic accountability in the Banking Union: is there really a gap?

Introduction

The creation of the Banking Union (BU) in 2012 represented an important change in the Economic and Monetary Union (EMU), and in the European Union (EU) in general. Indeed, it entailed the delegation of new competences in the areas of banking supervision and bank resolution to the EU level, and it demanded the creation of unique procedures and original governance mechanisms. It has no doubt represented a big step forward in the process of European integration as it is only the second area in which full integration is realized. 2 At the same time, it has also certainly increased the existing level of complexity within the EU. This is the case among other reasons because euro area Member States are part of the BU, but membership to the BU is also open to the rest of the Member States. In fact, in 2020, Bulgaria and Croatia availed themselves of this possibility to join the BU without having adopted the common currency. By creating a third category of Member States next to the EU27 and those that belong to the euro area within the EMU, the BU added a new layer of differentiation in an already largely differentiated Union. 3 As a result of this and of the (unaltered) EU legal framework on which basis it was created, the institutional architecture in which the BU is embedded, and the procedures that underpin it, are extremely complex. This is also the case because banking matters are of concern to all EU Member States since banks operate across the Internal market and are thus governed by its rules. Moreover, non-BU EU Member States are also naturally affected by the developments that happen within the BU, not least because BU banks commonly operate in non-BU Member States. 4 To make matters worse, whilst banking supervision and resolution are now the ultimate responsibility of an EU institution and agency (the European Central Bank (ECB) and the Single Resolution Board (SRB), respectively), national institutions continue to exercise part of the competences. A division of tasks is operated between various EU authorities on the one hand, and the national ones on the other. 5 Also, 1 Marie Sklodowska-Curie Individual Fellow, Law School, Sciences Po Paris. The present research was conducted as part of "IMPACTEBU", a project that has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 895841. I would like to thank Cristina Dias, Alessandro Giovannini and Daniela Quelhas for valuable comments, as well as all the participants of the LEVIATHAN Conference held on 23-24 September 2022. 2 Grundmann and Micklitz, 'The European Banking Union and Constitution -The Overall Challenge' in Grundmann and Micklitz (ed), The European Banking Union and Constitution -Beacon for Advanced Integration or Death-Kell for Democracy? (Hart 2019) 1-24. 3 As evidenced for instance by the different chapters contained in Fromage (forthcoming) and in ibid. 'Introduction' in Fromage (ed.), (Re-)defining Membership: Differentiation in and outside the European Union (Oxford University Press 2022) 4 See Smoleńska, 'Multilevel cooperation in the EU resolution of cross-border bank groups: lessons from the noneuro area Member States joining the Single Resolution Mechanism (SRM)', Journal of Banking Regulation 23 (2022), 42-53. 5 See further on this della Negra and Lo Schiavo, 'The Relationship between the ECB and the National Competent Authorities in the Single Supervisory Mechanism: Problems and Perspectives' in Beukers, Fromage and Monti within the Single Supervisory Mechanism (SSM), the ECB for instance supervises Significant Institutions (SIs) directly, whereas National Competent Authorities (NCAs) remain in charge of the supervision of smaller credit institutions (or Less Significant Institutions, LSIs). 6 The existing literature on democratic accountability in the BU has, so far, focused on the ECB in its quality as banking supervisor (ECB-SSM), and to a lesser extent on the SRB. 7 However, a comprehensive assessment of democratic accountability standards in this area of EU public policy requires that a more holistic, all-encompassing view is taken as only such an approach allows to determine whether the four goods that accountability should provide, which are openness, non-arbitrariness, effectiveness, and publicness, can be delivered. 8 This is precisely the perspective adopted in the present chapter, which aims at going beyond the mere analysis of the accountability mechanisms applicable to these two EU instances. Although both substantive and procedural accountability are considered, this chapter arguably already adds to the existing state of the art by providing a mapping of the accountability mechanisms in place considered altogether, that is from the inception -at the EU level -of the norms that are in force within the BU to their application by national and EU authorities.

To fulfil this objective, the present chapter is divided into four sub-sections. It first examines how the BU operates, and disentangles the various mechanisms in place, and the role of the different EU institutions and bodies within them (II). It then proceeds to map the existing democratic accountability mechanisms (III). The subsequent sub-section turns to the substantive part of the analysis, that is it considers how these mechanisms operate in practice (IV). The final section concludes by offering an assessment of the democratic accountability standards as they exist following the creation of the BU. It considers in particular whether any gap exists, whether in substance or in practice (V).

II.

Who does what and how? A mapping of the existing procedures The first substantive section of this chapter will detail the characteristics of the existing mechanisms and the specific role played by the various institutions and bodies involved therein.

For the purposes of this chapter, it suffices to note that European integration in the banking domain differs from what is the norm in other areas of the EMU, for instance because differently from what is the rule in the field of monetary policy, banking supervision is an area of shared competence in which the ECB does not adopt the necessary norms itself but, instead, applies those designed by the EU legislator and by the EU regulator. It is led to apply the standards primarily preparedfor the whole of the EUby an EU agency, the European Banking Authority (EBA), but which must be formally adopted by the European Commission to become legally binding. This notwithstanding, the ECB may also itself adopt certain norms such that the divide between supervisor and regulator is not as clear-cut as it could seem at first sight. 9

As noted above, two EU authorities are primarily in charge of banking supervision and resolution within the BU. Their status, as well as the legal bases that underpin their existence, are however radically different. Whereas the ECB is an EU institution in its own right, the SRB is an EU agency. Powers in banking supervision could be conferred upon the ECB thanks to the existence of a 'reserve of competence' contained in art. 127(6) Treaty on the Functioning of the EU (TFEU). It could nevertheless only be entrusted with new competences with regard to those BU Member States that also belong to the euro area, such that specific mechanisms had to be designed to allow the participation of non-euro area Member States in the BU. 10 By contrast, the SRB was created on the basis of art. 114 TFEU, an EU-wide Internal Market legal basis, even if only BU Member States participate in the SRM. 11 Considering all this, studying the democratic accountability standards of the BU requires a substantive and a procedural analysis of several accountability mechanisms in place, that is those applicable to the ECB-SSM, to the SRB but also those applicable to the EBA, to the Commission and even to the ECB in as far as the ECB's Governing Council ultimately is the organ that formally approves the supervisory decisions prepared by the ECB's Supervisory Board. 12 9 For instance: Brescia Morra 'From the Single Supervisory Mechanism to the Banking Union. To obtain a full picture of the existing situation, a multilevel perspective that considers the national dimension, as well as multilevel (administrative) cooperation and multilevel democratic accountability mechanisms should also be adopted. Considering the limited space available here however, this chapter will focus on the EU level and on the existing accountability mechanisms vis-à-vis EU institutions and bodies. The national and the multilevel dimensions will only be underlined and considered in as far as it is necessary to assess the EU dimension of this issue.

III.

Accountability mechanisms in place a. Accountability mechanisms applicable to the ECB The question of the ECB's accountability plays a primary role in the guarantee of high (or adequate) democratic accountability standards in the BU because, as noted, the ECB is in charge of banking supervision. Its Supervisory Boardwhich is an internal organ of the ECB created for the specific purpose of banking supervision created by the SSM Regulation -13 is in charge of preparing supervisory decisions, which are later adopted by the Governing Council following a non-objection procedure. Its involvement is necessary because according to the Treaties, the Supervisory Board is not a decision-making organ of the ECB. As such, both the mechanisms in place to hold the ECB-SSM and the ECB to account are of importance when considering democratic accountability of and within the BU. However, because the role of the Governing Council is secondary to that of the Supervisory Board, the mechanisms in place vis-à-vis the latter will be examined first.

The accountability of the Supervisory Board is to be ensured following procedures defined in the SSM Regulation. 14 Its article 20 is dedicated to "[a]ccountability and reporting". According to this provision, the ECB is accountable to both the Council and the European Parliament (EP) for the implementation of this Regulation. To this end, it shall submit every year a "report on the execution of the tasks conferred on it by this Regulation, including information on the envisaged evolution of the structure and amount of the supervisory fees" to the EP, the Council, the European Commission and the Eurogroup. That report shall be presented by the Chair of the Supervisory Board to the EP, and to the Eurogroup in presence of those Member States that participate in the BU but do not belong to the euro area (they are also involved in the procedures mentioned subsequently where reference to the Eurogroup is made). This format of the Eurogroup is known as the 'Eurogroup in BU format'. Both the Eurogroup and the EP also have the possibility (on an individual basis and independently from each other) to invite the Chair of the Supervisory Board to appear before them (or before the responsible committee in the case of the EP) to discuss the execution of its supervisory tasks. Oral or written questions may additionally be put to the ECB (that is, the ECB-SSM) by both the Eurogroup and the EP. 15 Next to these procedures, the possibility exists that, upon initiative of the Supervisory Board's Chair, confidential oral discussions behind closed doors be held with the Chair and the Vicechairs of the responsible EP Committee, that is the Committee on Economic and Monetary Affairs (ECON Committee), where these "are required for the exercise of the European Parliament's powers under the TFEU". The details of these arrangements are to be defined in an interinstitutional agreement between the EP and the ECB, agreement, which was adopted in 2013. 16 Finally, a duty is set on the ECB to cooperate with the EP in its conduct of investigations. To this end, "[t]he ECB and the European Parliament shall conclude appropriate arrangements on the practical modalities of the exercise of democratic accountability and oversight over the exercise of the tasks conferred on the ECB by this Regulation. Those arrangements shall cover, inter alia, access to information, cooperation in investigations and information on the selection procedure of the Chair of the Supervisory Board".

The Interinstitutional agreement details the content of the annual report, which the ECB has to submit to the EP. It also specifies that the Chair of the Supervisory Board shall be submitted at least to two ordinary hearings, although additional ad hoc exchanges of views may be organised too. Additionally, it specifies how the confidential oral discussions have to take place in practical terms. Likewise, the modalities for the submission of written questions are specified, and the aim is that the ECB answers them within five weeks (as opposed to the six-week target set for the questions put to the ECB by MEPs on monetary policy issues as per the EP's Rules of procedure). Specific provisions furthermore detail how information on the ECB's tasks as a supervisor are to be made available. This includes, for example, the access to the record of proceedings of the Supervisory Board by the ECON Committee, or non-confidential information regarding a credit institution that has been wound up. The EP is to establish sufficient safeguards for the confidentiality of the ECB documents submitted to it to remain preserved.

As noted previously, also the EU executives (e.g. Commission, Council and Eurogroup) are addressees of the ECB-SSM's annual report. What may, however, appear as more surprising is the fact that it is with the Eurogroup and not the Council with which the true relationship of accountability is established. Indeed, the annual report shall be presented to the Eurogroup, which may invite the Chair of the Supervisory Board to appear before it and submit both written and oral questions to the ECB-SSM. This state of fact is disturbing for several reasons. As recalled by the Court of Justice on several occasions, 17 the Eurogroup is not an institution of the Union but an informal group whose raison d'être it is to allow for the coordination of euro area Member States' policies. Neither the informal nature of the Eurogroup, nor the purpose of its existence square well with the role it is called to play in guaranteeing the ECB-SSM's democratic accountability. Moreover, according to art. 10 TEU, democratic accountability rests upon two pillars within the EU since the entry into force of the Lisbon Treaty: the EP and Member States government representatives participating in the Council. Considering all this, the ECB-SSM could rather have been held accountable by the Council. This would have made 16 International agreements 2013/694/EU, Interinstitutional Agreement between the European Parliament and the European Central Bank on the practical modalities of the exercise of democratic accountability and oversight over the exercise of the tasks conferred on the ECB within the framework of the Single Supervisory Mechanism, OJ L320/1. 17 all the more sense as the Council (and formally at least, not the Eurogroup) is involved in the approval of (part of) the secondary legislation the ECB has to apply in its quality as banking supervisor. Additionally, the argument can be made that developments within the BU are of interest to all of the EU Member States, as is indeed confirmed by the fact that BU matters are, at least in some instances, discussed in Eurogroup meeting in inclusive format, that is with representatives from all EU27 Member States. 18 The Lisbon Treaty already opened the door to a "differentiated Council", that is one within which on some occasions only euro area representatives may cast their vote and thus the Council could have been used as an accountability forum. Admittedly, since the possibility formally exists that non-euro area (candidate) Member States may join the BU, an accountability forum that would only bring together BU representatives had to be set up, and only the Eurogroup (and not the Council) could easily be adapted for that purpose. But it remains the case that the solution found is largely unsatisfactory for the reasons outlined previously.

Next to these relationships of accountability with EU organs, "relationships with national parliaments" are also foreseen in the SSM Regulation. Although formally, and according to the ECB itself, it is "primarily accountable to the EP" and not to national parliaments, and although the question as to whether these relationships between the ECB-SSM and national parliaments serve the purpose of democratic accountability has been subject to debate, 19 there is little doubt that the powers with which parliaments have been entrusted vis-à-vis the ECB (written questions, reasoned observations on the annual report and exchange of views) resemble those that commonly exist between parliaments and any institution they hold accountable.

These relationships of accountability add to those that have existed between the EP (and the Council) and the ECB since the creation of the ECB. Indeed, the ECB's (strong) independence is to be compensated by its relationship of accountability towards the EP (primarily). It must therefore address an annual report on "the activities of the ESCB [European System of Central Banks] and on the monetary policy of both the previous and the current year to the European Parliament, the Council and the Commission, and also to the European Council." 20 This report shall be presented to the Council and to the EP, which "may hold a general debate on that basis". Additionally, the possibility exists for the President of the ECB or the other members of the Executive Board to be heard before the ECON Committee on their own initiative, or on that of the ECON Committee. MEPs are also entitled to submit six questions for written answers to the EP. 21 In the framework of monetary policy, although some exchanges were indeed organised in the past, 22 formally no relationship exists between the ECB and national parliaments, as may appear logical considering that monetary policy is a competence of the Union. 23 The existence of a relationship of accountability between the ECB and the Council makes sense historically as, originally, the status of "Member State with a derogation", that is that of Member State outside the euro area, was meant to remain temporary for all Member States bar Denmark and the United Kingdom which had obtained a permanent opt out. Thus, correspondence largely existed between the geographical area within which the ECB's monetary policy would take effect (at that point in time or eventually), and the Member States represented in the Council. However, already at the time when the Lisbon Treaty was drafted it may be argued that this had become wishful thinking. This notwithstanding, Member States did not choose to change the identity of the forum in charge of holding the ECB accountable and instead the Council kept this prerogative, despite the fact that that is precisely that Treaty which formalised the existence of the Eurogroup. The choice in favour of the Eurogroup when the SSM was established could point to the willingness to further empower the Eurogroup, a forum which had already been significantly reinforced as a result of the euro area crisis. Furthermore, to state the obvious, a choice in favour of the Eurogroup is also to the benefit of the Member States since the accountability and transparency standards it is submitted too are much less stringent than those applicable to the Council. 24 b. Guaranteeing the SRB's accountability

The SRM was established a few years after the SSM, and the latter's accountability mechanisms no doubt inspired those of the former. Indeed, the obligations set on the SRB by the SRM Regulation are similar to those set on the ECB-SSM by the SSM Regulation. 25 However, considering that the SRM is an agency and not an EU institution like the ECB, it is accountable not only to the EP and the Member Statescoming together in the Council and not in the Eurogroup, but also to the Commission. The annual report is submitted to the EP, the national parliaments of participating Member States, the Council, the Commission and the European Court of Auditors. As a result of this, differently from what is the case within the SSM, the Eurogroup is not supposed to be involved in any way in this instance, which could be the case because the SRB is an EU-wide agency. The report is then presented to the EP and the Council. The EP may additionally invite the Chair of the SRB to a hearing, and a minimum of one hearing per year is set by the SRM Regulation. Written and oral questions may be submitted to the SRB by the Council and the EP, and the possibility to hold confidential oral discussions is also provided. Like it is the case between the ECB-SSM and the EP, an agreement that details the 23 Relationships have still developed on an informal basis since the Eurocrisis. Whether they serve information/pedagogical purposes or are deemed to serve as an additional accountability channel for the ECB (or whether they ought to) is up for debate. See Fromage Changing parliaments in a changing European Union (Hart forthcoming). 24 See further on the Eurogroup's accountability: Markakis, in this volume. 25 modalities of these discussions shall be concluded; 26 and the SRB is set to cooperate in any investigation the EP may initiate.

Like the Interinstitutional between the ECB-SSM and the EP does, the Agreement between the EP and the SRB details the content of the report that the SRB has to submit every year. The topics addressed in the ordinary public discussions is also defined, as is the possibility to organise ad hoc meetings and the practical modalities of the confidential oral discussions. A minimum of two ordinary hearings per year is set. The EP shall be kept duly informed as a "comprehensive and meaningful record of the proceedings" of every executive or plenary meeting is to be submitted to it within the six weeks that follow said meeting. The rest of the provisions contained in the Agreement are similar to those included in the Interinstitutional agreement between the ECB-SSM and the EP.

Likewise, the SRM Regulation establishes a direct relationship between the SRB and the national parliaments of the participating Member States. Their nature (that is, whether they constitute a relationship of accountability) is also not specified, but as they are very similar to those established with the EP they may also be viewed as contributing to the SRB's accountability credentials. The powers vested with national parliaments in this framework are indeed very similar to those attributed to them vis-à-vis the ECB. However, the SRB is set under stronger obligations towards them than the ECB is. 27 c. The EBA's accountability credentials Guaranteeing democratic accountability within the BU demands that also the EBA be submitted to democratic control. This is the case because it prepares technical standards that are officially adopted by the European Commission at a later stage, and because it still fosters coordination among National Competent Authorities, including but not only in areas closely linked to banking supervision.

The accountability mechanisms applicable to the EBA were significantly enhanced when the European Supervisory Authorities (ESAs) Regulations were amended in 2019. 28 In its original version, the ESAs Regulation only established that "[t]he Authorities referred to in points (a) to (d) of Article 2(2) [among which is the EBA] shall be accountable to the European Parliament and to the Council". By contrast, it is now foreseen that the EBA be accountable to the EP and the Council, but that it shall also cooperate with the EP in the event that the latter decides to conduct an investigation. Despite the EBA's quality as an agencyand differently from the 26 Agreement between the European Parliament and the Single Resolution Board on the practical modalities of the exercise of democratic accountability and oversight over the exercise of the tasks conferred on the Single Resolution Board within the framework of the Single Resolution Mechanism. 27 SRBthe EBA is not accountable to the Commission. Several reasons could account for this. Perhaps the most evident one is that this provision not only concerns the EBA (or the ESAs), but also the European Systemic Risk Board (ESRB), which is not an agency but an independent body chaired by the President of the ECB. The EBA's prerogatives are also more circumscribed than those of the SRB. The Commission is called to formally adopt the normative acts, which the EBA prepares such that it already is in a position to exercise some form of control over its actions, although the procedures differs for non-normative acts. The EBA's "Board of Supervisors shall adopt an annual report on the activities of the Authority, including on the performance of the Chairperson's duties, and shall, by 15 June each year, transmit that report to the European Parliament, to the Council, to the Commission, to the Court of Auditors and to the European Economic and Social Committee". As such, the duty that is now set on the Board of Supervisors is similar to the one, which the ECB-SSM and especially the SRB have to fulfil. However, in this case a precise date is set by which the EBA has to fulfil its obligation, and the European Economic and Social Committee is, too, an addressee of the report.

Additionally, it is prescribed that the EBA's Chairperson be heard by the EPupon its request -at least once a year "on the performance" of the EBA. The format of the hearing is quite precisely defined in the Regulation, as it calls for the Chairperson to make a statement and to answer the questions put to it by MEPs. The EP may ask the Chairperson to report on the activities of the EBA at least 15 days before the hearing. Specific mention is also made to the possibility for the EP to request that the EBA reports on its participation in international forums, which is all the more welcome as those (which include, for instance, the Basel Committee on Banking Supervision 29 ) have assumed an ever larger role following the outbreak of the Great Financial Crisis.

Next to these procedures, the possibility also exists for the Council or the EP to put written questions to the EBA, which it shall answer within five weeks. Like it is the case with the ECB-SSM and the SRB, confidential oral discussions may be organised since the EBA Regulation was amended.

d. The Commission

One last actor that arguably plays an important role in the BU is the European Commission. This is the case for numerous reasons, chief of which are the facts that it is involved in several of the procedures that exist (for instance, in banking resolution), that it has the last word on the standards developed by the EBA, and naturally also that it proposes the norms of secondary legislation that are of application within the BU.

In consequence, upholding suitable accountability standards within the BU demands that the Commission be submitted to sufficient controls. Put differently, in seeking to evaluate whether 29 any accountability gap exists within the BU, one should also check whether the Commission's actions in this domain are sufficiently scrutinized by the EP.

The EP has numerous means to hold the European Commission to account. Its strongest power lies in its possibility to remove its confidence to the Commission and thus to force it to resign collectively. 30 The EP and its members may also put some oral and written questions to the Commission or submit it to major interpellations, 31 organize hearings to provide an opportunity to the Commission to explain its decisions, 32 and create committees of inquiry. 33

e. Conclusion

The preceding analysis has evidenced that mechanisms exist to guarantee the democratic accountability of BU institutions. An evolution towards an enhancement of these mechanisms may additionally be witnessed, both in terms of their nature as well as in terms of their very existence. Indeed, the accountability of the EBA was significantly reinforced following the reform performed in 2019. Also, the mechanisms in place towards both the ECB-SSM and the SRB are more stringent than those applicable to the ECB. Several reasons may account for this. First, the ECB benefits from a stronger degree of independence in the area of monetary policy than it does in the field of banking supervision. 34 Second, accountability standards have evolved significantly over the past twenty years. For example, the EP is only consulted when the President of the ECB is appointed. In contrast, its consent is necessary for the chair of the Supervisory Board to be nominated, 35 that is the EP's role has become larger over time.

Accountability mechanisms, be them formalized or not, make it more likely that democratic accountability is upheld. However, the mere existence of those mechanisms does not suffice, as there is, for example, no guarantee that they are used by the actors to which they are available. The next sub-section therefore turns to the practice of accountability in the BU to date.

IV. The practice of democratic accountability so far

To evaluate the practice of democratic accountability so far, two dimensions in particular will be considered: formal accountability, that is if and how the existing instruments have been used, and substantive accountability, that is what these mechanisms have been used for in terms of substance. The data examined in this sub-section covers the period between November 2014 and April 2022, that is from the start of the functioning of the SSM until the date of submission. It consists of minutes of EP debates, written questions and the responses they received, as well as the yearly reports produced severally by the institutions examined. 36 The focus is set on the ECB-SSM, the SRB and the EBA owing to the ECB and the European Commission playing a secondary role in the BU if compared to the ECB-SSM, the SRB and the EBA.

Before proceeding with the proposed analysis, it should be noted that any conclusion drawn at this stage may only be provisional since the two pillars of the BU have only been functioning for a short period of time. This notwithstanding, the proposed study is still valuable because it allows to gain some knowledge of how the existing mechanisms have been used and which shortcomings inherent to them or gaps among them may exist. The conclusion thus provides an assessment of the current situation, as well as some suggestions for improvement.

a. Practice of accountability to date

It must be said from the start that research reveals that the existing democratic accountability procedures have been used indeed: Parliamentary hearings and ad hoc exchanges of views have been organised, reports have been produced and parliamentary questions have been put to the ECB-SSM and to the SRB. However, differences in terms of frequency and fluctuations over time have existed. The following paragraphs first consider the ECB-SSM before turning to the SRB and to the EBA.

As regards parliamentary questions put by MEPs to the ECB-SSM, it must first be said that they were not very numerous in the first years of the functioning of the SSM, as in only logical. They peaked in 2017 and 2018 although they remained infrequent at approximately 40 questions per year (by comparison, the number of the questions put to the ECB as the European institution in charge of monetary policy was similar in 2017 but it rose to more than three times this amount in 2018). 37 The number of questions has since been decreasing and there was only a dozen of them in 2021. Perhaps this could be explained by varying level of interests among participating MEPs, with notably one of the most active of them, Sven Giegold, having ceased to be an MEP. Also, the SSM no longer is a new instrument, thus MEPs' interest could have faded with time, in particular seeing as no new banking crisis has emerged and as the ECB thus seems to be fulfilling its tasks satisfactorily. It could be expected that MEPs' interest would rise again if the ECB-SSM were to deal more closely with controversial issues such as climate change. Despite recommendations in favour of the creation of a space dedicated to questions posed by MEPs to the ECB-SSM (and the SRB), [START_REF] Smits | Study Requested by the ECON committee: SSM and the SRB accountability at European level: room for improvements?[END_REF] no such step has been taken by the EP to date beyond the possibility that exists to use the filter function on its website, which is regrettable as it makes relevant information harder to find. Also, some questions have been put by national members of parliaments, most often from the German Bundestag. It is perhaps unsurprising that the members of the Bundestag are those that have used this mechanism most considering the fact that the creation of the BU had raised concerns that democratic accountability standards would be lowered as a consequence thereof. Indeed, the German NCA, the BaFin, is functionally placed below the responsibility of the ministry of finance, which may be held accountable for the actions of the NCA. 39 More generally, and perhaps most importantly, a tradition exists for German MPs to ask written questions. In terms of their content, some of the questions are very specific and regard a specific credit institution, whilst others are much more general and address for instance non-performing loans, the implementation of the Basel standards or supervision in general. Such a mixed set of macro-and micro-topics seems to be healthy for the whole system of supervision.

Parliamentary hearings and ad hoc exchanges of views, as well as hearings before the Eurogroup have taken place on a regular basis, and the annual reports were duly presented. Though some fluctuations over time may be observed in this regard as wellperhaps also due to the pandemic and the widespread 'Zoom-fatigue', it may generally be said that exchanges with MEPs have been more frequent than the minimum set by the SSM Regulation as they have often included a couple of ad hoc exchanges of views in to the standard bi-annual hearings. 40 The topics covered during these exchanges were varied as they ranged for example from the consequences of the pandemic to climate risks and the finalisation of Basel III.

Confidential oral discussions have taken place before hearings of the Chair of the Supervisory Board by the ECON Committee, and they have been 'reported to be much more confrontational than public hearings, with 'tough' language that is often absent in public interactions between the two institutions'. 41 Finally, the Chair of the Supervisory Board has regularly appeared before the Eurogroup, and these meetings have commonly been organised together with the Chair of the SRB (this is examined more in depth below). Transcripts of these hearings have been made available since 2019. Fluctuations in their frequency have existed as well, with notably 2017 standing out as a year of particularly close exchanges, but this was also the year when the first resolution ever took place such that this is perhaps rather unsurprising. As these exchanges are not public, they are harder to assess. Nonetheless, the ECB had noted in the past that '[t]he topics of interest to the finance ministers overlapped to a large extent with those discussed in the European Parliament', 42 and the overall issues discussed may be found in the account of the main results of Eurogroup meetings since they exist. The topics covered have included for example broader issues such as non-performing loans, and anti-money laundering.

If one considers the SRB, one may first regret that the part devoted to accountability in its annual reports remains particularly succinct. Also, it appears that its exchanges with the EP have been less frequent than those organised between the ECB-SSM and the EP as they have generally been limited to two exchanges per year in addition to the presentation of the annual reports. This could be explained by the fact that the SRM has only been activated on one occasion during the period considered here. On the other hand, the fact remains that the setting up of the SRM has raised questions indeed, in terms of its functioning and its financing, but also in relation to questions related to the overall architecture of the BU and notably its missing 39 Thiele, Finanzaufsicht: der Staat und die Finanzmärkte, (1 st Ed, Mohr Siebeck, 2014), p. 415f. 40 2021 is a notable exception to this, which the need to resort to a virtual format could perhaps explain. 41 Akbik, The European Parliament as an accountability forum: Overseeing the Economic and Monetary Union, (1 st Ed, Cambridge University Press, 2022), p. 77f. 42 European Central Bank, 'Annual report on supervisory activities', March 2018. Accessed via https://www.bankingsupervision.europa.eu/press/publications/annualreport/html/ssm.ar2018~927cb99de4.en.html (14.05.2022). pilar, the European Deposit Insurance Scheme, and the role the SRB could play therein. Therefore, more interest on the side of MEPs could have been reasonably expected.

MEPs have likewise devoted much less attention in their questions to the SRB than they have to the ECB-SSM. To date, they have addressed 15 questions in total, of which seven were addressed by the same MEP (Sven Giegold). 43 These questions have sometimes consisted in requests for access to documents, or more general questions such as the architecture of the SRM in general, as well as questions on the Banco Popular case, for Like it was the case with the ECB-SSM as well, questions from national parliaments have not been numerous (10 in total) and only German MPs have asked questions to date. The identity of these MPs largely corresponds to those who raised questions to the ECB-SSM. Interestingly, although the answers to these questions are available on the SRB's website, they are not translated into English but are, instead, only available in German. Whilst this is understandable as translation is demanding on resources, one may wonder whether this does not, in fact, diminish the SRB's accountability potential vis-à-vis the larger public. Considering how few these questions are, it would be advisable for the SRB to make a courtesy translation available to all. As concerns the topics touched upon by these letters, they have regarded very factual issues including the number of credit institutions whose resolution planning the SRB oversees, as well as questions related to specific credit institutions or related to findings of the European Court of Auditors.

The relationship between the SRB and the Eurogroup follows a similar pattern as the one between the ECB-SSM and the Eurogroup, not least because the Chair of the Supervisory Board and the Chair of the SRB commonly appear together before the Eurogroup. Issues addressed with the Chair of the SRB have included resolution planning, the built-up of the Single Resolution Fund or resolvability (continuity seems to exist in the topics discussed, which is only logical as the SRB's main task in normal times is to prepare for potential resolution cases such that the issues that need addressing are rather recurrent as opposed to being individual events). It must be noted that although this practice of joint hearings with the Chair of the Supervisory Board and the Chair of the SRB makes perfect sense as they allow for a more comprehensive control by the EP of what is going on in the BU, it remains that it contradicts the content of the SRM Regulation, which foresees that the SRBan EU-wide agencybe held to account by the Council. As noted above, it probably would have been best to entrust the Council with the task of controlling both the ECB-SSM and the SRB in the first place, also to guarantee higher transparency and thus higher accountability standards.

The relationship between the SRB and the Commission seems to unfold on a smooth basis, as the SRB noted for instance in its annual report for the year 2020 that it 'continued to maintain its close cooperation with the relevant directorates-general of the Commission, in particular with the Directorate-General for Financial Stability, Financial Services and Capital Markets Union (DG FISMA) and the Directorate-General for Competition (DG COMP) at all levels on various aspects, which are relevant to the SRB's work and functions, and participated actively in the meetings of the Expert Group on Banking Payments and Insurance (EGBPI)'. [START_REF]Single Resolution Board[END_REF] Further details are not available.

Finally, one may regret that the information regarding the EBA's accountability is not much detailed; its annual reports and its website indeed only contain scarce information on this topic, and it is not easy to find. The EBA fulfils its duty to present its annual report to the EP, and it entertains relationships with the other EU institutions. 45 Most of the correspondence publicly available is addressed to the European Commission, and it covers issues that go beyond banking supervision owing to the EBA's broad mandate. This notwithstanding, some of the letters are indeed addressed to MEPs, but they remain scarce. 46

b. Conclusion

The preceding analysis of the use of the existing accountability mechanisms to date reveals first that information on this issue is scattered around the various websites and uneasy to find. This is regrettable and efforts should be made to improve this situation, as already proposed by René Smits.

Second, it appears that, at the EU level, the existing procedures are being used indeed, as hearings and exchanges of views are organised, questions are posed, and reports are produced. The EP additionally produces annual reports on Banking Union, and the ECB and the Commission generally react to these. 48 Parliamentary questions are, though, rather infrequent, and fluctuations have existed over time in the frequency of the oral exchanges held. It is interesting to note that despite its duty to hold the EBA accountable too, the EP only keeps regular records of practice of accountability towards the ECB-SSM and the SRB, but not towards the EBA (or any of the European Supervisory Agencies). [START_REF]Single Supervisory Mechanism: Accountability arrangements (9 th parliamentary term)[END_REF] This is regrettable as the EBA, and these agencies in general, play an increasingly important role in financial supervision within the EU, and as the acts of soft law they adopt produce significant effects for banks and have been the object of litigation before the Court of Justice. [START_REF]Fédération bancaire française (FBF) v Autorité de contrôle prudentiel et de résolution[END_REF] In any event, shortcomings exist in the practice of accountability: despite the fact that external experts are regularly invited to produce briefings, the questions put by MEPs are not always sufficiently to the point. 51 Most importantly, the same questions are not consistently picked up during debates. 52 Also, MEPs are not always clear about the appropriate forum or addressee for a specific issue. For instance, some of the questions put to the ECB were not addressed to it in the right set up, that is MEPs mixed up the set up designed for dialogue on monetary policy issues with the one reserved to banking supervision. Although this confusion could have been due to the very numerous forums in which MEPs have the opportunity to debate with the ECB, it could also be the case that they deliberately choose not to care for political reasons and simply use any channel they have at their disposal.

Beyond all this, it has been found that, in effect, MEPs only have had limited influence on the ECB-SSM's policy, although this is because MEPs only rarely require such changes but rather use their interaction with the ECB to request information on policy views. 53 This could point to a usage of public hearings and questions primarily for communication purposes, as opposed to their being used for accountability purposes. 54 Confidentiality in banking supervision is a further hindrance in MEPs' quest for accountability, 55 and reform proposals have been made to improve this situation. 56 Finally, and although this issue is only subsidiary to the analysis conducted here, one may observe that very limited use has been made by national parliaments of the possibility they now have to directly interact with the ECB-SSM and the SRB. To assess whether this results in an accountability gap, research should determine whether this is compensated by adequate mechanisms of accountability towards NCAs and the use thereof by parliaments at the national level.

V. Conclusion: is there a gap and if so, how to bridge it

This chapter intended to adopt a holistic view on democratic accountability in the BU with a view to determining whether any gap exists. Some gaps appear to exist indeed, and they derive from a. the EU's constitutional framework, b. the BU's architecture and its characteristics, and c. from practice, that is how the existing accountability mechanisms are used.

a. The EU's constitutional framework has become unfit for purpose

The existing flaws are both generally related to the EU's architecture and functioning, and specific to EMU.

The shortcomings inherent to the EU's architecture are twofold, and are caused by, on the one hand, the trend of agencification within the EU, [START_REF]The Agency Phenomenon in the European Union: Emergence, Institutionalisation and Everyday Decision-Making[END_REF] and relatedly to the absence of specific and precise legal basis for EU agencies, which would allow a much necessary update and adjustment of the Meroni doctrine. On the other hand, they derive from the gap that has grown between the existing legal framework, and the degree and the variety of differentiation within today's EU (where differentiated integration is understood in the largest possible sense). As noted above, the co-existence of the BU, the euro area and the EU-27 and the corresponding institutional variations of the meetings of national ministers at the EU level certainly blur the boundaries between the various groups of Member States, and thus the accountability channels applicable to the various procedures. This then must bring back to a reflection on the question of (internal and external) differentiation and membership within the EU more generally.

Some of the existing shortcomings are, though, specific to the EMU and its sub-area the BU. Whereas differentiation is a feature commonly observed within the EU and not specific to the EMU, the EMU is arguably the most extreme example of differentiation in terms of its breadth and reach with among others the ECB conducting the euro area's monetary policy, or the existence of an intergovernmental European Stability Mechanism as an emergency safety net reserved to euro area Member States but one that also serves as a backstop to the (EU) BU. Differentiation within the EMU is then also visible in terms of its institutional embedding with the Eurogroup as a quasi institution, the existence of Euro Summit, of specific voting rules in the Council, and the recurrent proposals in favour of a euro area parliament or at least a euro area sub-committee to the ECON Committee, [START_REF] Curtin | Differentiated representation: is a flexible European Parliament desirable?[END_REF] to the point that the principle of institutional unity that used to be a requirement to any initiative of enhanced cooperation under Amsterdam could come under threat. 59 As has been evidenced in this chapter, the mechanisms formally in place within the BU are oftentimes pragmatic solutions to the lack of suitability of the existing legal framework as is illustrated by the Eurogroup's role in guaranteeing the ECB-SSM's accountability. Practice shows a further adaptation of the established mechanisms as in the case of the Eurogroup, which also serves as accountability forum for the SRB. Both of these phenomena nonetheless only illustrate that the existing institutional framework is unfit for purpose, because it has not been adapted to match the evolutions that have happened in the breadth of the policies conducted at the EU level and to the form that these take, even if it must be admitted that the framework currently in place has proven to be sufficiently flexible for informal arrangements to be developed.

b. Flaws inherent to the BU

Finally, democratic accountability within the BU does not solely rest on EU institutions and bodies; national institutions, too, play a large role. This is the case because they approve national legislation as noted previously, because they remain competent in areas that are closely linked to BU matters (for instance: anti-money laundering) and because they are closely involved in the functioning and the operation of both the SSM and the SRM.

c. How to bridge the existing gaps?

If all were best in the best of possible worlds, differentiation within the EU would vanish, that is the three currently co-existing categories of Member States, which the EU27, the euro area and the BU form would disappear. Thus, some of the regulatory gaps and of the institutional complexity would cease to exist.

Likewise, if Treaty change were a realistic option, a better design for EU agencies could be introduced, a proper legal basis for the BU could be created including the formal acknowledgement of a third category of Member States next to the euro area and the EU27, that is that of BU Member States. A true discussion on whether the ECB should be the BU's supervisor could be had, and the Chinese wall that separates its monetary policy from its banking supervision functions better designed.

However, unfortunately, none of these options seem to be realistic at this stage of European integration. Even the Conference on the future of Europe is unlikely to lead to the full opening of Pandora's box, as it might do it but only in specific areas with a specific objective. 63 It is true that following Brexit the most adamant advocate of the interests of non-euro area Member States is gone, and no non-euro area Member State has as large a financial market as the UK used to have such that none of them has its leverage in EU27-negotiations. But a discussion on Treaty change would likely regard many areas other than the BU and taking account of all the challenges they are already facing internally including the economic recovery post-COVID, the threats to the rule of law and to EU values, or the ecological and digital transition, EU Member States may not want to take this path at this point in time. Neither would they realistically be in a position to find a compromise solution at this stage if one considers how long they have been unable to come to a compromise solution on the completion of the BU, for instance.

If Treaty change is not an option, what is, then? In addition to the solutions already included in the main sections of this chapter, one could consider additional avenues to improve the existing situation.

First, institutional engineering, that is the improvement of existing practice through the actions of the institutions involved themselves should continue to be exploited. Institutional engineering commonly takes the form of arrangements put in place by institutions on an informal basis or their promoting regulatory change. In a nutshell, it means that institutions use their margin of discretion and action to the largest extent possible. One form this could take would consist in the creation of a dedicated BU sub-committee of the ECON Committee, a possibility that was already considered for the euro area in 2013-2014, and which could build 63 The EP did call for the constitution of a Convention, but it is unclear whether it will be constituted. upon the already existing Banking Union Working Group. 64 This would allow for some of the MEPs to become more specialized in BU matters, and they would not necessarily all have to stem from BU Member States.

Changes in secondary legislation (and in primary law where this is easily feasible) should also be considered with a view to upgrading the mechanisms in place, and to simplifying the existing architecture where possible.

Further harmonisation at the EU level should be pursued too, both in terms of the norms applicable, but also perhaps in terms of the minimum requirements set with respect to the features of the national institutions involved. At present, NCAs and NRAs are hosted by very different institutions that correspond to different national traditions and rules. Arguably, if for instance the applicable standards of independence were more strongly defined at the EU level it would be easier to guarantee democratic accountability in this area, as the institutional set ups would be less complex. 65 It may thus only be hoped that the Court of Justice will be called to continue to perform its duty of clarification and definition of the tasks and responsibilities of the different institutions involved within the BU.

Lastly, it may also only be hoped for that MEPs and MPs will improve the use they make of the existing mechanisms. This would include, as mentioned, asking more informed questions, making more demands for policy changes where necessary, and ensuring better synergies between the mechanisms that exist in parallel. To this end, interparliamentary cooperation should also be fostered, for instance the Interparliamentary Conference on Stability, Coordination and Governance could be better exploited: to date, it has only rarely addressed BU-related matters. But other mechanisms should be established too, in the form of interparliamentary committee meetings hosted by the EP, and on the initiative of the Presidency parliament and with the involvement of national parliaments only.

As reforms to improve and complete the BU are high on the EU's agenda again,66 it is urgent that they be also accompanied by matching improvements of the democratic accountability mechanisms in place in the whole of the BU.

64

See Fasone and Curtin, supra n 58. See on the Banking Union Working Group: https://www.europarl.europa.eu/committees/en/econ/econ-policies/financial-services?tabCode=banking-unionwg (consulted on 23.5.2022). 65 The institutional embodiment of NCAs and NRAs is an issue, which has been largely neglected by research to date in the sense that there have not been large comparative studies of it. The EBA recently published the outcome of a survey on independence, which allows to gain some insights. Additionally, in the proposal of reform of the Capital Requirements Directive issued in October 2021, the requirements in terms of the independence of the NCAs are significantly enhanced. Proposal (COM/2021/663 final) for a directive of the European Parliament of the Council amending Directive 2013/36/EU as regards supervisory powers, sanctions, third-country branches, and environmental, social and governance risks, and amending Directive 2014/59/EU.

  Joined Cases C-597/18 P, C-598/18 P, C-603/18 P and C-604/18 P Council of the European Union v Dr. K. Chrysostomides & Co. LLC, and the other parties whose names appear in Annex I [2020] ECLI:EU:C:2020:390, paras 62f.; Markakis and Karatzia,' Financial assistance conditionality and effective judicial protection: Chrysostomides', Common Market Law Review (2022), 59, 501-542.

  Art 45 and 46, Regulation (EU) No 806/2014 of the European Parliament and of the Council of 15 July 2014 establishing uniform rules and a uniform procedure for the resolution of credit institutions and certain investment firms in the framework of a Single Resolution Mechanism and a Single Resolution Fund and amending Regulation (EU) No 1093/2010, OJ L 225/1 (hereafter SRM Regulation).

  In particular, to date no substantive analysis of the use of accountability mechanisms within the SRM have been performed. Recent analyses include: Amtenbrink and Menelaos, 'Towards a Meaningful Prudential Supervision Dialogue in the Euro Area? A Study of the Interaction Between the European Parliament and the European Central Bank in the Single Supervisory Mechanism', European Law Review (2019) 1, 3-23; Fromage and Ibrido, 'Accountability and Democratic Oversight in the European Banking Union' in Schiavo (ed.

(eds.), The 'New' European Central Bank: Taking Stock and Looking Ahead (Oxford University Press (forthcoming)).

6

The specific role of the ECB and the NCAs has given rise to somewhat diverging interpretations by the Court of Justice of the EU and the German Federal Constitutional Court in their L-Bank and European Banking Union decisions, respectively. See Landeskreditbank Baden-Württemberg -Förderbank V European Central Bank (ECB) and BVerfG [2019] ECLI: DE:BVerfG:2019:RS20190730.2BVR168514, paras. 1-320; See for some comments on these cases: Annunziata.

'

European Banking Supervision in the Age of the ECB: Landeskreditbank Baden-Württemberg-Förderbank v. ECB', European Business Organization Law Review (2020) 21, 545-570; Schammo, 'Matching or Clashing? Landeskreditbank Baden-Württemberg v ECB and the Decision of the German Bundesverfassungsgericht on the Banking Union', Durham University, 28 November 2019. Accessed via http://dx.doi.org/10.2139/ssrn.3495226 (16.05.2022). 7 ), The European Banking Union and the role of law, (Edward Elgar. 2019), 66-86; Vlachou, 'Ensuring the democratic accountability of the Single Resolution Board: Which role for the European Parliament and national parliaments?', Revue internationale des services financiers/International Journal for Financial Services, (2017) 1, 8-20; Božina Beroš and Beroš, 'The Single Resolution Board: What About Accountability?', in Pollak and Slominski (eds.), The Role of EU Agencies in the Eurozone and Migration Crisis, pp. 127-148. 8 See further the introductory chapter to this edited volume.

  The Role of the ECB and the EBA', LUISS Guido Carli School of European Political Economy, working papers, 13 June 2014.

	Accessed via https://papers.ssrn.com/sol3/papers.cfm?abstract_id=2448913 (16.05.2022); To ensure consistency
	between the actions pursued by the EU legislator and those pursued by the ECB, a specific procedure of
	cooperation has been established by means of the Interinstitutional agreement concluded between the EP and the
	ECB. See: International agreements 2013/694/EU, Interinstitutional Agreement between the European Parliament
	and the European Central Bank on the practical modalities of the exercise of democratic accountability and
	oversight over the exercise of the tasks conferred on the ECB within the framework of the Single Supervisory
	Mechanism, OJ L320/1.
	10 This is the so-called "close cooperation" regime defined in art. 7 SSM Regulation. See on practice to date: Beck
	and Bruno, 'The ECB's close cooperation on supervising banks in Bulgaria and Croatia', In-depth analysis for the
	EP ECON Committee, PE 699.521 (2022) and Darvas and Martins, 'Close cooperation for bank supervision: The
	cases of Bulgaria and Croatia', In-depth analysis for the EP ECON Committee, PE 699.523 (2022).
	11 See for a discussion on the resort to this legal basis: Tuominen 'The European banking union: a shift in the
	internal market paradigm?', Common Market Law Review 54 (2017), 1359-1380.
	12 The exact role of the ECB in the approval of SRB decisions was also unclear but eventually the Court of Justice
	designated the SRB as the sole decision maker. See ABLV Bank AS and Others v European Central Bank [2021]
	ECLI:EU:C:2021:369, paras 58f; Budinská, 'Op-Ed: "Of auctoritas and potestas in the Banking Union: The ECB,
	the SRB, failing credit institutions and judicial review"', EU Law Live (2021) .

  Lamandini and Ramos Muñoz, 'Study Requested by the ECON committee: SSM and SRB accountability at European level: What room for improvements? Banking Union Scrutiny', European Parliament, April 2020. Regulation (EU) 2019/2175 of the European Parliament and of the Council of 18 December 2019 amending Regulation (EU) No 1093/2010 establishing a European Supervisory Authority (European Banking Authority), Regulation (EU) No 1094/2010 establishing a European Supervisory Authority (European Insurance and Occupational Pensions Authority), Regulation (EU) No 1095/2010 establishing a European Supervisory Authority (European Securities and Markets Authority), Regulation (EU) No 600/2014 on markets in financial instruments, Regulation (EU) 2016/1011 on indices used as benchmarks in financial instruments and financial contracts or to measure the performance of investment funds, and Regulation (EU) 2015/847 on information accompanying transfers of funds (Text with EEA relevance), OJ L 334/1.

	Accessed	via
	https://www.europarl.europa.eu/RegData/etudes/STUD/2020/645711/IPOL_STU(2020)645711_EN.pdf
	(11.5.2022).

28

  See on this: De Bellis, 'Reinforcing EU financial bodies participation in global networks: addressing legitimacy gaps?' In: Hofmann et al (eds.) The External Dimension of EU Agencies and Bodies Law and Policy (Cheltenham: Edward Elgar Publishing (2019)), pp. 126-144; Fromage, 'The (multilevel) articulation of the European participation in international financial for a: the example of the Basel Accords', Journal of Banking Regulation 23 (2022), 54-65; Viterbo, 'The European Union in the Transnational Financial Regulatory Arena: The Case of the Basel Committee on Banking Supervision', Journal of International Economic Law 22, 2 (2019), 205-228.

  /www.bankingsupervision.europa.eu/press/speeches/date/2022/html/ssm.sp220301~66eb4805eb.en.html (16.05.2022).35 See on this evolution: Fromage, 'Guaranteeing the ECB's democratic accountability in the post-Banking Union era: An ever more difficult task?', Maastricht Journal of European and Comparative Law (2019) 26, 1, 48-62.

	30 Art. 18 (7) TEU.
	31 Art. 230 TFEU and Rules 136, 137, 138 and 139, Rules of Procedure of the European Parliament (2019)
	32 Rule 133, Rules of Procedure of the European Parliament (2019).
	33 Art. 227 TFEU and Rule 208, Rules of Procedure of the European Parliament (2019)
	34 As recalled for instance by Kerstin af Jochnick, Member of the Supervisory Board of the ECB on 1 March 2022.
	Supervisory independence and accountability. Af Jochnick, 'Speech by Kerstin af Jochnick, Member of the
	Supervisory Board of the ECB, at the IMF High-Level Regional Seminar in Sub-Saharan Africa', European
	Central	Bank,	1	March	2022.	Accessed	via
	https:/

Art. 26 (1), Regulation (EU) No 468/2014 of 16 April 2014 of the European central bank establishing the framework for cooperation within the Single Supervisory Mechanism between the European Central Bank and national competent authorities and with national designated authorities (SSM Framework Regulation), OJ L

141/1 (hereafter SSM Framework Regulation 2014).14 Council Regulation (EU) No 1024/2013 of 15 October 2013 conferring specific tasks on the European Central Bank concerning policies relating to the prudential supervision of credit institutions, OJ L 287/63.15 Note though that the questions submitted to the ECB in that framework are deducted from the total of six questions MEPs may ask every month as per art. 140 EP Rules of procedure. Likewise, the questions addressed by MEPs to the SRBto which more beloware also deducted from this maximum number of six-monthly questions: See Rule 141, Rules of Procedure of the European Parliament (2019).

This was notably the case on the occasion of the meeting of 12 July 2021. See European Council, 'Meeting of Eurogroup, 12 July 2021', July 2021. Accessed via https://www.consilium.europa.eu/en/meetings/eurogroup/2021/07/12/ (16.05.2022).

Fernández Bollo, 'Democratic accountability within the framework of the SSM and the SRM as a complement to judicial review' in Zilioli and Wojcik (ed), Judicial Review in the European Banking Union -Elgar Financial Law and Practice series (Edward Elgar Publishing Ltd (2021)), .

Art 15 (3), Protocol (No 4) on the Statue of the European system of central banks and of the European central bank, OJ C 202/230, (here after ESCB Statute).

Rule 140 (1), Rules of Procedure of the European Parliament (2019)

Jančić, 'Accountability of the European Central Bank in a Deepening EMU' in Jančić (ed), National Parliaments After the Lisbon Treaty and the Euro Crisis -Resilience or Resignation? (Oxford University Press, (2017)) 141-158.

This data was used either directly, or via the proxy on analysis available in the literature duly referenced in footnotes.

Some, like the one by MEP de Lange of 6 December 2016, were raised during hearings held before the EP.

This was notably noted by Fabian Amtenbrink and Menelaos Markakis, as well as by Adina Maricut-Akbik. Supra n7 and Maricut-Akbik, 'Contesting the European Central Bank in Banking Supervision: Accountability in

Ammann, 'Eurogroup president launches new push to complete banking union', euractiv.com, 4 May 2022. Accessed via https://www.euractiv.com/section/economy-jobs/news/eurogroup-president-launches-new-push-tocomplete-banking-union/ (13.05.2022).

Next to these shortcomings related to the EU's institutional framework, there are also shortcomings that are specific to the BU, although they partially derive from the problems that exist within the EU's constitutional structure generally.

The BU is in-between the EU27 and the euro area, and relies on both structures. From this derives inherent complexity that in turns makes guaranteeing democratic accountability particularly challenging. Accordingly, democratic accountability standards within the BU may not be assessed by only looking at the ECB-SSM and the SRB. As this chapter has posited, other actors including the Commission and the EBA play an important role as well, and their accountability credentials must, too, be taken into consideration.

Mark Bovens has defined accountability as 'a relationship between an actor and a forum, in which the actor has an obligation to explain and to justify his or her conduct, the forum can pose questions and pass judgment, and the actor may face consequences'. [START_REF] Bovens | New Forms of Accountability and EU-Governance[END_REF] When the last step is taken within the framework of the BU, that is when the forum that holds the agent to account is to take actions based on its assessment of how the principle has performed, it must hold not only the ECB-SSM or the SRB to account, but also the and the EBA because of their role as regulator. The ECB's nature as an independent EU institution and as a central bank also acting as banking supervisor complicates matters further, as does the EBA's and the SRB's nature as independent agencies. As a result of the ECB's numerous functions, accountability becomes more difficult to ensure because the same group of MEPs are called to regularly interact with the ECB in different capacities, thus demanding from them that they first identify in which forum they must ask which kinds of questions. In any event however, as recently noted by the former Governor of England Paul Tucker, "[t]he European Parliament's Econ committee is too big to conduct effective oversight of the ECB's stewardship of the monetary regime". [START_REF] Tucker | How the European Central Bank and Other Independent Agencies Reveal a Gap in Constitutionalism; A Spectrum of Institutions for Commitment[END_REF] The same could be said of the ECON Committee when it is called to hold the ECB-SSM to account although in that context, the possibility for smaller meetings to be organised in the form of confidential oral discussions may partially contribute to solve this problem. Be this as it may, even if Paul Tucker is certainly right in considering the EP ECON Committee to be too large an accountability forum, it is difficult to imagine which other format would have sufficient legitimacy based on its representativeness of the (large) euro area to play such a role. Furthermore, other practical problems outlined below may in fact be a bigger hindrance to effective accountability than the ECON Committee's large size.

Beyond all this, because the EU does not have exclusive competence in the field of banking supervision and bank resolution, national authorities continue to play a large role. Additionally, harmonisation is only partial such that the applicable rules vary across the BU and EU organs, and primarily the ECB, have to apply national norms upon whose content and legality they have no control. 62