### 11.1 [PERSON] ()  
Italian Aerospace Research Centre--CIRA, Via Maiorise, 81043 Capua, Italy; [EMAIL_ADDRESS]  
The formation of ice can be very dangerous to flight safety, especially in cold climates, since ice accumulated on the surfaces of the aircraft can alter the aerodynamics, increase the weight, and reduce lift, leading to catastrophic stall situations in some cases. Currently, risks caused by ice accretion are mitigated by using energy-demanding active ice protection systems (IPSs), which work by either preventing ice (anti-icing) or removing ice (de-icing). However, for future sustainable aviation, low-energy-demanding IPS must be designed. Hybrid IPSs, which combine active IPSs with passive superhydrophobic/icephobic coatings, able to prevent, delay, and/or reduce the ice accretion, might represent a valuable solution, reducing the energy consumption and the CO\({}_{2}\) emissions [1, 2, 3, 4, 5]. Recently, [PERSON] et al. [6] found that the combination of icephobic coatings with electrochemical heating IPS reduces the energy requirements by more than 70% at LWC of 0.6 g/m\({}^{3}\) and a median volume diameter (MVD) of 15 um at 75 m/s. However, in wet icing conditions, more than a 30% reduction in power is achieved. A reduced power consumption by more than 50% compared with IPS without coatings was also observed by [PERSON] et al. [7], which demonstrated the ability of superhydrophobic coatings to prevent run-back ice. In this scenario, this Special Issue collects research achievements, ideas, chemical formulations, applications of superhydrophobic and icephobic coatings as passive IPS working alone or in combination with active IPSs, IPS parameter design, and icing wind tunnel (IWT) test campaigns, covering diverse technologies and application domains, such as aeronautical and energetic. Some studies have focused on the design of the hybrid IPSs, providing numerical tools able to simulate the effects of superhydrophobic and icephobic coatings under icing conditions [8], including the sensitivities of IPSs to icing environmental parameters [7]. These first results demonstrated that it is actually possible to predict the beneficial effect of properly designed coatings for ice mitigation purposes in real-world applications [8]. Physical parameters, coating compositions, structure, roughness, morphology, and durability are properties not to be neglected in the design and development of reliable IPSs in aircraft maintenance [9]. In addition to high superhydrophobicity or icephobicity, a protective coating to be used on aircraft must meet comprehensive property requirements, such as workability, heat and low temperature resistance, weatherability, erosion durability, and reparability. Among these, erosion resistance is one of the most important; for instance, coatings applied to the leading edge of a wing or helicopter rotor blades, where icing tends to occur and cause the most negative impact on aircraft operation, may experience excessive wear due to the high-speed (e.g., 100-300 m/s) impact of sand, airborne dust, rain droplets, and hail [10]. Elastomeric coatings with water contact angles ranging from 100 to 115\({}^{\circ}\), high mechanical strength (19-27 MPa), high elongation at break (640-730%), and low tensile set (20-35%) have been demonstrated to reduce the ice adhesion from 622 kPa to 480-220 kPa, while combining excellent erosion resistance against both high-speed solid particles and water droplets [10]. The question remains as to whether such coatings could provide durability and performance in relevant flight icing conditions. Superhydrophobic coatings were demonstrated to be helpful in reducing the ice accretion by 12% to 100% at temperatures higher than \(-12~{}^{\circ}\)C and velocities of 50 and 95 m/s during an IWT test campaign carried out on coatings applied on two NACA0015 wing profiles, with no active IPS switched on [11].