And why is it needed…

Recent very cold weather in UK and Europe has once again highlighted the need for de-icing and anti-icing. In some parts of the world it’s a daily occurrence. So, what’s involved?

Aircraft and ice are sworn enemies. Whilst systems have been developed to prevent icing whilst in the air, on the ground things are vastly different. If you’re expecting it to be a similar process to clearing your car windscreen and windows, think again!

The whole aircraft goes through a process which involves the simultaneous use of several vehicles. Clearing flight-critical surfaces is paramount to ensuring the “clean wing” principle is maintained for sufficient time to get airborne. Ice impairs the aerodynamics by adding drag and weight. If control surfaces are allowed to ice up, then the combined effect of reduced lift plus increased weight and drag requires a compensating increase in the angle of attack, thrust and fuel consumption. This gives the potential for altitude loss and reduction of the aerodynamic stall margin. Ice isn’t choosy where it forms. It can accumulate on pistons rotary or jet. Thus the airflow intake is restricted and potentially causing aerodynamic imbalance (propellors) or ingestion damage (jets).

However, airborne icing doesn’t just occur in winter. It can happen at low positive temperatures down to -40°C, mostly at around 10,000 feet. Whilst water can exist unfrozen below 0°C in the atmosphere, the moment it comes into contact with an aircraft, it immediately freezes. Also, tanks containing “cold soaked” fuel can spend hours at cruise temperatures. They act like a radiator in reverse. Cold radiates along the inner metallic structures, freezing any condensation that collects on the wing.

What are the main ingredients of de-icing agents? The main one is a freezing point depressant (FPD). This reduces the temperature at which a substance freezes. Glycol of various strengths is used, categorised into types I-IV in ascending protection order. It’s vital the correct mix is applied. These are identified by colour; I orange, II yellow and IV green. III is bright yellow and only used on smaller aircraft. Type I is a 50/50 water/glycol mix for easy run off. It’s usually used when there’s been an overnight frost. All fluids provide protection for what’s known as a holdover, the information identified in airport weather forecasts. After de-icing, there is usually the anti-icing stage with type II-IV fluids which avoid wing re-contamination. These are more complex, made up of propylene glycol mixed with water and pseudo-plastic thickener. Thus, the run off time is lengthened.

Ultimately, de-icing decisions are made by the captain based on aircraft type and operator manuals. We all know that ice can freeze clear, so often a touch test is carried out. This is often done via rigs known as cherry pickers. The process may be conducted on stand with engines off, or on a remote pad with engines sat idle. This depends on airport facilities. Whilst type I fluid is delivered under high pressure, types II-IV are dispensed at a lower pressure to ensure it remains in place. One area that is not sprayed is the flightdeck windows and the vital probes around the nose. The frost/snow is either removed by brushing or with hot air. Off course, if there is a slot delay, the entire process may have to be repeated.

Once airborne, the aircraft systems monitor the outside temperature and any icing that may occur. Bleed air is often pumped around the engine nacelles and leading edges of the wings.

As our local council road gritting teams may start their winter preparations in October, it’s the same for airport de-icing teams. They conduct rehearsals to ensure skills are honed and equipment is in good working order. A key part of the total process in reality is pilot and ATC ground interaction.

And finally….

Jet2 - gave an amazing send off to their last B757 on 8 January. Crowds gathered at MAN Runway Visitor Park and on Southside to capture this historic moment. MAN based staff, LBA staff and off-duty ATC joined the many spotters in freezing conditions. G-LSAI taxied pas the spectators twice before departing R23L to DGX. Sadly, due to weather conditions the flypast at LBA was cancelled, also the wing wave at MAN. Various YouTube streamers captured the event. Airliners Live, Simon Lowe Aviation, etc.

Information courtesy of Airliner World (Feb 2025), Jet2

Images courtesy of FR24, S D Bail Aviation on YouTube

©TPSC, LadyJet2 and photo/diagram suppliers