The world of helicopter ice protection systems
Flight in icing conditions is a significant safety threat affecting EMS and SAR helicopter operators. Mario Pierobon reports
historically there have not been reliable data collected as to how operationally significant the icing threat is
Flight in icing conditions is a significant safety threat affecting EMS and SAR helicopter operators. However, it’s difficult to quantify exactly how many missions are lost during the winter months because of ice.
“In the old days, it was the case that when the helicopter pilot faced icing conditions, s/he would not fly at all, and therefore historically there have not been reliable data collected as to how operationally significant the icing threat is,” say Luca Medici, head of helicopter system design, and Matteo Ragazzi, chief of airworthiness, at helicopter manufacturer Leonardo.
As ice protection system installations were made available by helicopter manufacturers, operators started to aggregate more data. “There is, however, a significant degree of variation amongst the different providers as to the number of missions that cannot be flown due to icing conditions. In the North Sea, an operator has estimated somewhere in the 10 to 15-per-cent range the amount of lost missions because of ice during the winter months. In the area of the Russian island of Sakhalin in the North Pacific Ocean, the estimate is in the range of eight per cent. These are significant values in terms of aircraft productivity. There is no consolidated figure yet, however operators are starting to be more concerned and aggregating more solid data,” say Medici and Ragazzi.
Rega’s experience
Helicopter rescue provider Rega realised that there are hundreds of missions that it was not able to perform across Switzerland every year because of weather conditions. The service therefore approached Leonardo Helicopters to highlight the need for an intermediate light helicopter that allows operations under all conditions, and Leonardo launched the development of a full ice protection system (FIPS) for the AW169. At the time of writing, there are no Rega helicopters equipped with FIPS – or even a limited ice protection system (LIPS).
Heinz Leibundgut, chief pilot (helicopters) for Rega, comments: “As Rega operates no helicopter with FIPS or LIPS, there are no operational [existing] practices. As flying in icing conditions is not an option, we have to cancel or abort missions during icing conditions. Today, we are able to perform IFR in non-icing conditions only.”
Rega maintains a positive outlook on the future availability of FIPS on the AW169 and it foresees being able to perform many more missions safely. “Every year, bad weather currently prevents around 600 people in Switzerland from receiving emergency assistance from the air. Rega wants to change this situation and in future help even more people in distress. It has therefore launched a series of measures that will enable its helicopters to also be able to fly when visibility is poor,” says Leibundgut. “Rega is, among other things, working closely with the Swiss Air Force and the Skyguide air navigation service to establish a network of instrument flight routes. This so-called Low Flight Network (LFN) is based on satellite navigation (SBAS and RNP 0.3) and will link [with] airfields with permanent IFR infrastructures, as well as hospitals and smaller airfields with specially designed approaches. In December 2016, the two main routes of the LFN (south to north and east to west) were finally established and operational. Two weeks later, Rega flew its first patient from the southern part of Switzerland on the LFN over the Alps.”
Another important piece of the puzzle is the purchase of a helicopter that is all-weather capable, but within an acceptable weight range, which will take Rega a major step closer to its vision of performing all-weather rescues. “As of 2021, it is foreseen that the new FIPS-equipped AW169 helicopter will initially be stationed at two Rega bases and deployed to defy the harsh weather conditions,” says Leibundgut. “In contrast to the actual fleet of AW109s and EC145s, the AW169 will be able to perform IFR flights in icing conditions. With regard to the topography of Switzerland with alpine mountains and peripheral valleys, the AW169 will be very useful for performing IFR flights in icing conditions on the Low Flight Network (LFN), for example flying patients from a regional to a central hospital.”
Ice protection systems
Leonardo Helicopters ... was the first manufacturer to bring a FIPS to the market for light and medium category helicopters.
Leonardo Helicopters has committed to differentiate its products by equipping them with ice protection systems and it was the first manufacturer to bring a FIPS to the market for light and medium category helicopters. “The AW139 was the first intermediate helicopter to make it to market equipped with a FIPS. The same holds true for the larger AW189 and the light intermediate AW169. The latter will be the only light helicopter to come equipped with a FIPS,” says Medici. “Paradoxically, the smaller the helicopter, the higher the negative impact of icing. Once there [is] certification of the AW169’s FIPS, it will be indeed an industry first as there is no other small helicopter equipped with a FIPS.”
The AW189’s FIPS was certified by the European Aviation Safety Agency (EASA) in mid-2016, allowing the aircraft to operate in full icing conditions when other helicopters would be grounded. The EASA certification came after three years of flight trials in Northern Europe and North America during the winter months to gather data and test the effectiveness of the system.
Leonardo Helicopters’ experience with ice protection systems stretches also to the military domain, where its ice-protected AW101 can fly in temperatures down to -20⁰C and with ice accretion of up to 80 mm (more than three inches). There are currently 15 AW101 units operated by the Canadian Air Force for SAR purposes and equipped with ice protection systems. And there are over 70 ice-protected AW139s operated all over the world: these include seven units operated by Sweden’s SMS for SAR and 10 units operated by Canada’s ORNGE for EMS. There are more than 20 ice-protected AW189s, and they include 11 units operated in the UK and two operated in the Falklands for SAR.
there are over 70 ice-protected AW139s operated all over the world
An ice protection system is made of several interconnected components. First of all there is engine anti-icing. “We have an anti-icing system that does not allow any ice accretion on the engines and this works by means of valves which make hot air circulate through the compressor blades and the particle separator,” say Medici and Ragazzi. “An anti-icing role is played also by the air vents, which are heated, as well as by the windshield. In addition, we have an ice and snow detection system which [assesses the] severity of the icing conditions where flight is being undertaken and leads to the heating of the main rotor and tail rotor blades.”
Full or limited?
There are two main categories of ice protection systems available from Leonardo Helicopters – FIPS and LIPS. “As far as the FIPS is concerned, the Ice Control Box (ICB) component works as the brain of the system and it has the function of managing all the components that make up the whole,” say Medici and Ragazzi. “From the cockpit, the ICB allows [the helicopter] to accomplish automatic and manual FIPS operations. Automatic operation requires, for example, an ice detection system which provides information as to the icing severity and, based on certain conditions, informs the operator how much the blade heating system must be active. The whole is connected with the air data system through the outside air temperature (OAT) sensor and the pitot tube, and we have an AC/DC electrical power generation system which brings electrical power to the main and tail rotor blades.”
The difference between a FIPS and a LIPS is that the limited version does not have the components to create the electrical power needed to heat up the blades. “The blades are not heated, and a certain amount of ice accretion is tolerated under certain relatively high temperature conditions (up to minus 10⁰C) and, once the limitations are exceeded, the aircraft must get out of the icing conditions – it has to reduce altitude and reach areas where there is warmer air,” say Medici and Ragazzi.
There is an important component that is common to both the FIPS and the LIPS: the SLD (super-cooled large droplet) marker. The SLD marker is an icing condition detection system and it requires pilot monitoring. “It is a visual indicator, a simple sphere with some coloured strips: black, yellow and red. If you have ice accretion on the black or yellow strips it means the helicopter is still being flown in normal ice accretion conditions. If you have ice accretion on the red strip, it means that the conditions are severe and the helicopter must leave these conditions,” explain Medici and Ragazzi.
The LIPS systems are sold in particular in Northern Europe, say Medici and Ragazzi, where typically a pilot can simply reduce altitude to escape icing conditions – any ice accretion then either melts or detaches from the aircraft. Operators who want a FIPS-equipped helicopter tend to be those that operate in more extreme weather conditions, they add: “The FIPS is critical for operators flying in Canada, Russia and the northern US, where icing conditions are common during the winter months. There are also, however, other operational conditions that may dictate the choice for the FIPS instead of the LIPS. EMS and SAR operators, for example, may not be able to plan or forecast icing conditions and the related need to reduce altitude, and therefore prefer the FIPS because it allows flight in ice without limitation, except for flight above 10,000 ft and in SLD conditions, where droplet size is large and ice extends to unprotected parts of the aircraft and forms larger shapes.”
Operational benefit
The AW169 will help us to expand our scope of operations and bring us closer to Rega’s vision for an air rescue of ‘anytime, anywhere, any conditions’
Rega believes that it can provide improved emergency medical care from the air by equipping its future AW169s with the FIPS. “Among those who will profit from instrument flight routes and FIPS are people living in the peripheral regions, who in a medical emergency can be flown to a central hospital no matter what the weather. For example, even despite low cloud cover and icing conditions, Rega will be able to fly premature babies from Samedan, which is located in the mountain valley of Engadin, via the instrument flight route over the Julier Pass to Chur or Zurich. Babies that are born before the 34th week of pregnancy need to be transferred to a central hospital. In such cases, it is vital that the patient spends a minimum amount of time away from the hospital, so the fastest transport possible is of key importance. Until now, with icing conditions, the only possibility has been a lengthy journey by road. Other intensive care patients will also benefit from the new flight procedures of the AW169,” says Leibundgut. “The AW169 will help us to expand our scope of operations and bring us closer to Rega’s vision for an air rescue of ‘anytime, anywhere, any conditions’. It will also improve primary healthcare in Switzerland, as if necessary we will be able to fly patients from remote regions such as mountain valleys to a central hospital, even if the mountain passes are covered in cloud or if visibility is poor.”
As it approaches its AW169 experience, Rega will develop best operational practices for dealing with ice in EMS and SAR operations in the alpine environment, including training. Leibundgut says: “It is too early to be specific, as requirements depend on the outcome of the AW169 certification process. Once we have all the data, we will be able to design and define our standard operational procedures for the AW169.”
Although Leibundgut acknowledges that there will still be conditions where missions are impossible even with ice protection-equipped helicopters, such as freezing rain or very strong winds, Rega is en route to a greatly enhanced service.