Flying anytime, anywhere, in all-weather conditions is one of the most challenging technology and capability goals across the rotorcraft industry to meet a growing demand for reliability, safety and the ability to allow platforms and their operators to deliver whenever needed. Countering the detrimental and dangerous effects of ice on rotorcraft is part of this mission and Leonardo Helicopters has devoted significant efforts over the years to design, develop, test and integrate ice protection systems onto its current generation production aircraft models.

A range of applications can benefit from ice protection systems including onshore/offshore transport and short-to long-range rescue duties. The military market is no exception. Depending on geographies and missions, customers can require different kinds of dedicated systems ensuring varying degrees of protection stemming from the various levels of icing condition severity. Although it can be hard to determine the number of missions lost by operators globally during winter months due to ice, customers’ estimates indicate 10-15% operations lost in the North Sea, while around 8% of operations can't be carried out for the same reason in the North Pacific Ocean and Sakhalin Island (Russia). Swiss Air Rescue Rega stated that over 600 missions are aborted every year, also due (but not only) to icing conditions.

Leonardo Helicopters was the first OEM to introduce ice protection systems onto intermediate to medium category helicopters (on AW139 and AW189 respectively, between 2010 and 2016) and will be the first one to introduce such a system onto light helicopters (AW169) and commercial tiltrotors (AW609). The AW101, which can also be provided with an ice protection system, is currently being used in Canada for SAR (search and rescue) purposes, allowing it to fly in temperatures down to minus 20° Celsius and ice accretion of up to 80 mm. More than 70 AW139s and over 20 AW189s are ice protected with a dedicated system worldwide for a range of missions including offshore transport, SAR, and passenger transport.

The development of ice protection systems for the AW139 intermediate twin and the AW189 ‘super medium’ involved test aircraft performing icing trials in North Europe and North America for up to three years during the winter months. Certification campaigns were launched that saw the aircraft flying both into artificial and natural ice, verifying flight characteristics and system performance, gathering data, and testing the effectiveness of the system, which includes electrically heated main and tail rotor blades, heated windscreens and an ice detection system. Trials were performed with the support of a US Army CH-47 HISS (Helicopter Icing Spray System) simulating ice clouds, under the supervision and with the involvement of the appropriate certification authorities such as EASA, FAA and TCAA.

Leonardo Helicopters developed two different types of ice protection system: the Full Ice Protection System (FIPS) and the Limited Ice Protection System (LIPS), both available as options. The FIPS and LIPS keep performance and procedures for Cat. A operations unchanged, and generate no restrictions during IFR operations.

Full Ice Protection System

Redstone Test Center's icing team uses a HISS-equipped CH-47 to create an artificial ice cloud for testing. (Photo: RTC)

The FIPS allows the AW139 and AW189 to fly into more extreme, known icing conditions that would confine other helicopters in their categories to the ground or in the hangar. The FIPS system includes ice detectors, an automatic activation system with manual back up, electrical power generators, engine intake protection grids, and heated windshield and blades (main and tail rotor). The standard AW189 helicopter already includes an engine air intake heating system. The system is fully automatic once switched on by the pilot, allowing the crew to concentrate on other flying activities.

The anti-icing system prevents ice accretion on the engines by means of valves circulating hot air through the compressor blades and the particle separator. The air vents and windshield are also heated. An ice and snow detection system allows the crew to assess the harshness of the icing conditions and heats the main rotor and tail rotor blades.

Core to the FIPS is the Ice Control Box (ICB), which manages the whole system, manually or automatically, with appropriate cockpit controls. The detection system provides the pilot with info on the ice severity level, helping to determine when the heating system has to be activated. The system architecture includes an air data system through OAT sensor and Pitot tube, while an AC/DC power generation system powers the blades.

Another icing condition detection system that is part of the FIPS is the Super-Cooled Large Droplet marker (SLD). This system consists of a black/yellow/red colored sphere visually indicating whether the aircraft is flying in normal ice accretion conditions (black), or if they are becoming too harsh to continue (red), so that the crew understands when those conditions have to be abandoned and the craft moved towards a safer status. Actually, the only conditions suggesting no flying activities should be carried on for safety reasons are ice accretion on the red side of the SLD sphere and over 10,000 ft. The FIPS is particularly useful for operators flying in Northern Europe, Canada, Russia and the northern United States where icing conditions are common during the winter months.

The FIPS can be a preferred option for SAR/EMS operators who need to deliver 24H, 7 days a week and need the greatest level of versatility and availability with no weather forecast and altitude reduction limits. Under the so called ‘Project Icebird’, an essential part of the Rega vision – “fly everywhere, anytime, in any weather” – the operator is developing, together with Leonardo Helicopters, a highly customized rescue configuration of the new generation AW169 light intermediate twin which will be provided with a FIPS system. This will require overcoming some challenges due to the small size of the aircraft.

Limited Ice Protection System

The LIPS is a variant of the FIPS that, thanks to its cost-effectiveness and reduced weight, is optimal for flight in limited ice conditions, typical, for example, of the North Sea. The LIPS permits flight within a known and defined envelope of icing conditions (up to minus 10° Celsius), provided that the capability to descend into a known band of positive temperature is available throughout the intended route. This is typical of conditions encountered, as mentioned above, over the North Sea. Thanks to its reduced weight, LIPS is optimal for flight in limited icing conditions for various operations. The LIPS system includes ice detectors, Super-Cooled Larger Droplet (SLD) marker, Ice Accretion Meter and heated windshield. The system does not require heated rotor blades and associated equipment/electrical generator (like for the FIPS). The aircraft with LIPS has only limited restrictions in terms of low temperature and ice presence during IFR operations, therefore expanding the all-weather operating capability.

The next iteration of ice protection systems at Leonardo will include the AW609 TiltRotor and advanced research on a totally new approach. The third prototype of the AW609 started icing trials in North America in March 2017. As far as new technology demonstrators conceived for future rotorcraft, Leonardo also developed and successfully tested a new system in recent years designated De-Light (De-Icing System for Light-Intermediate Helicopters). Shape Memory Alloys-based technology has been implemented and incorporated into a main rotor blade segment leveraging mechanical actuation able to remove ice accretion on the leading edge.

This article was written by Matteo Ragazzi, Head of Airworthiness, Leonardo Helicopters (Boston, MA). For more information, Click Here .