## 1 Introduction  
Search and rescue missions can be hazardous and dangerous for emergency teams, especially when winter conditions bring about snowy, stormy, or icy precipitation that adheres to emergency vehicles. The situation becomes even more difficult when rescue teams need to use aircrafts such as helicopters. If a life is in danger, the operation becomes a critical mission; therefore, rotorcraft need to be dispatched, takeoff, and land safely in any condition to successfully complete their mission. De-icing at the base is normally easier with appropriate tools, or if the rotorcraft is kept inside a hangar, icing challenges can be minimized [1]. However, the major issues may occur when they are deployed on a mission. Sometimes, ice or wet snow can deposit and adhere quickly on the critical surfaces, and it needs to be removed before an eventual takeoff. This becomes especially limiting when rotocrafts are deployed to remote locations where de-icing capabilities are limited, and the crew need to rely on primarily manual methods (such as brushes or brooms) to remove snow and ice. In a subfreezing environment, ice in the form of rime and glaze may accumulate on the surface of rotorcraft blades [2]. Rotor blades covered with a thin ice layer can have a strong negative impact on aerodynamics. Increases in drag and flow separation, which significantly reduces lift and can often make controlling the aircraft extremely difficult [3; 4; 5; 6; 7]. Therefore, designing methodologies that prevent ice accumulation, reduce its adhesion, or even assist during the de-icing are incredibly important in eliminating the latter issues [2]. The following sections will review the main methods presently used for this application. Innovative de-icing and anti-icing protection systems have been developed and studied by numerous researchers. Several of these methods have also been investigated regarding their effectiveness in a laboratory setting prior to deployment in actual operations. The two main methodologies that have been explored are the following:  
* Active methods; and
* Passive methods. Active methods are those requiring external energy sources to work; they are divided in two main categories. The thermal methods consist of increasing the temperature of a critical surface to which ice may have formed or adhered. This is done to reduce ice adherence, by creating a water layer between the ice and the surface, and consequently allows for its removal under the effect of gravity. Some of these methods can also be used as a form of anti-icing. By increasing the temperature of the critical surface, it can effectively prevent supercooled water droplets from freezing upon impact. Some rotorcrafts are equipped with an electrothermal ice protection system for the main rotor blade, which can prevent grounding even in inclement icing conditions. Unfortunately, due to the significant energy load necessary for heating, the high electrical current in the slip rings, and the extensive cabling needed, approved electro-thermal de-icing systems can currently only equip the primary rotors of large rotorcrafts. However, this de/anti-icing methodology requires a significant amount of energy and adds a considerable amount of weight to the aircraft. In addition, it does not allow for the complete de-icing of the rotorcraft [5; 7; 8]. The mechanical methods consist of using tools that break the ice adhering to the aircraft structure by shocking or inducing vibrations [7; 9; 10; 11; 12]. In most cases, mechanical methods can be considered as de-icing methods since they are used to speed the shedding process after snow or ice has accumulated or formed on the structure. Studies show that mechanical methods require approximately 100,000 times less energy than thermal methods to induce ice shedding [13]. The principal mechanical methods are based on two strategies:  
* One consists of breaking the ice by means of scraping, rollers, hooks, cutters or rope; and
* The other consists of releasing energy from shock waves or vibrations to break and remove the ice.