Jerry Lewis, Chief Technical Officer for Kilfrost and Co-Chair of the SAE International G-12 Aircraft Deicing Fluid Committee, reflects on the evolution of aircraft deicing fluids and the innovations shaping the future of aviation safety.
In the 1930s, aviation faced serious winter risks from ice accumulation on aircraft, affecting both lift and control. Joseph Halbert, founder of Kilfrost, developed the first commercial aircraft deicing fluid, revolutionising winter aviation safety. His work was inspired by the natural antifreeze properties of the snowdrop flower, which survives cold conditions through antifreeze proteins (AFPs) that prevent ice formation within its cells.
Like the snowdrop’s mechanism, the first aircraft deicing fluids were designed to lower the freezing point of water using monopropylene glycol (MPG). This innovation laid the foundation for aircraft deicing practices today. However, as aviation grew, so did the need for more advanced formulations, leading to the development of longer lasting fluids with anti-icing capabilities to prevent re-freezing. This, then, is the story of safer winter aviation.
Challenges in winter aviation safety
The accumulation of ice can significantly reduce aircraft performance, decreasing lift by up to 50% and increasing drag by up to 200% (Flight Training Hub, 2022). Uneven ice distribution further impairs control of the aircraft. To address this, Halbert’s deicing fluids used glycol-based formulations, much like the snowdrop’s proteins, to melt ice and prevent its reformation for a limited period of time. These early fluids, now known as Type I, were effective at removing ice and snow but offered a limited window of time for protection against refreezing.
However, deicing fluids were essential for meeting the “clean wing” requirement, which is the current regulatory standard that mandates critical surfaces be ice-free before take-off. As aviation expanded, and weather conditions became more challenging, better protection was necessary through higher performing formulations.
Polymer additions and anti-icing fluids
To improve the performance of deicing fluids, polymers were introduced to them to give a higher viscosity and hence provide a thicker glycol layer on critical aircraft surfaces. These polymers, such as polyacrylates, generate a film that provides greater protection and extends the ice-free time, crucial during freezing precipitation events. The newer fluids became known as anti-icing fluids, Type II, Type III and Type IV. Of these, the majority of commercial products are the Type II and Type IV fluids.
The higher level of ice-free protection afforded by these newer fluids gives rise to the concept of “holdover time” – essentially the window of time that the aircraft can be expected to be protected from frozen precipitation before refreezing. This is a key requirement when considering the time needed by aircraft to taxi from their stands to the appropriate runway point ready for take-off.
The precise control of film thickness is an essential factor in optimising holdover time. As the fluid dilutes over time, its freeze point rises, making thicker films more effective in providing long-lasting anti-icing protection. Eventually, after enough snow or ice has been absorbed, the fluid will fail and freeze. Holdover time is thus finite.
Clearly, more polymer and better formulations could make the layer thicker and thicker. However, there is also a downside. Just as frozen contamination on the wings can destroy lift and control, a layer of thick and gelatinous glycol can also lead to a similar compromise in aerodynamic properties.
We now come to the key performance properties of Type II and Type IV fluids. While they are viscous at rest, they must thin out under mechanical stress, such as crucially by airflow over the wings during take-off. This shear-thinning behaviour allows the fluid to stay in place when the aircraft is stationary (providing protection against refreezing) but flow off easily during acceleration (shear thin and eliminate), ensuring that no residual fluid interferes with aerodynamics. The aircraft then has a clean wing at the point of rotation during take-off.
This need for high viscosity at rest and shear thinning under stress is hence the fundamental performance property balance that all modern anti-icing fluids must strike.
The development of aviation deicing standards
The SAE International G-12 Fluids Committee has developed global deicing fluid standards to ensure aviation safety during winter operations. Introduced to mitigate risks of ice formation on aircraft, these standards include Aerospace Materials Standards AMS1424 and AMS1428, which specify fluid physical property performance for different weather conditions. Additionally, Aerospace Standards AS6285 and AS6286 set guidelines for aircraft ground deicing procedures and ground crew training respectively. The primary goal is to deliver the “clean aircraft concept,” ensuring no frozen deposits or anti-icing fluid residues remain on critical surfaces at take-off. These standards play a crucial role in ensuring best practice for safe winter air travel.
Advances in fluid technology
Future innovations in deicing technology are likely to focus on improving both performance and sustainability. Research into bio-based polymers and eco-friendly additives such as anti-corrosion chemicals aim to reduce the environmental footprint of deicing fluids. Additionally, efforts to refine shear-thinning rheology and further enhance the holdover time of these fluids will continue to drive the industry forward. With growing environmental concerns, formulations and processes are increasingly focused on improved recycling methods or glycol management techniques to mitigate potential ecological damage.
The evolution of deicing and anti-icing fluids, from Joseph Halbert’s early glycol formulations to today’s sophisticated shear-thinning, environmentally conscious solutions, reflects the ongoing commitment by the industry to innovation in aviation safety.
