Why do planes need de-icing and how is it done?

In winter, ice formation can have negative effects on aircraft operation, and is a risk factor that is taken very seriously.

And since we’re at the start of winter, let’s take a look at the subject so that you can be totally reassured and understand what happens if the plane you’ve just boarded undergoes a de-icing procedure before the flight.

How does ice form on an aircraft?

Simply put, frost forms when water meets a surface at sub-zero temperatures.

On the ground it’s a phenomenon we all know and understand, but ice can also form in flight. Clouds are made up of suspended drops of water, and the tops of cumulonimbus clouds are made up of ice crystals.

However, ice forms mainly between 0 and -15°, while the temperature at cruising altitude is usually around -50°. We’ve seen ice form at -40°, but it’s very rare.

The most critical phases are therefore mainly during ascent and descent, or when flying at low altitude.

What are the risks of icing on an aircraft?

The first risk of icing, easily understood by a neophyte, is that of loss of visibility, but this is so obvious that we won’t dwell on the subject.

The main risk of icing is aerodynamic, even in the case of light icing.

Simply put, ice reduces lift and increases stall speed, reduces horizontal speed and climb rate.

More rarely, ice detached from air inlets and ingested by engines can cause them to burn out.

Ground de-icing

Two procedures can be applied to the ground: de-icing and anti-icing.

De-icing

This involves removing the snow and ice covering the aircraft by projecting a jet of heated liquid. A mixture of glycol and hot water (approx. 80°) is used.

The mechanism is as follows: the pressure of the jet pierces the layer of snow or ice to reach the fuselage (mechanical effect) and the heat melts it (thermal effect).

The chemical action of glycol also has a residual effect, preventing the formation of frost for a relatively short time after the operation, allowing time to wait for the application of an anti-icing fluid.

Anti-icing

The liquid used is similar in composition to that used for de-icing, except that it is not heated and is applied in the form of a shower rather than a jet.

A few millimeters of viscous liquid is applied to all surfaces to be protected. Its effectiveness is limited in time, but longer than that of de-icing fluid.

There are different types of fluid, depending mainly on the thickening agents used, the desired duration of protection or the type and speed of the aircraft.

In-flight de-icing

We have seen that ice can form in flight, so aircraft are equipped with devices to prevent it.

Several devices are used.

– Pneumatic inflation of bladders on the leading edges of lifting surfaces to break ice.

– Diffusion of de-icing fluid on certain parts of the aircraft.

– Reheating with hot air drawn from the engines.

Electric heating by resistors.

How common are icing-related aircraft accidents?

Icing is a frequent phenomenon, and according to an NTSB study, 173 icing-related accidents were recorded between 1982 and 2000.

Some of them were fatal. Not much, but more than in the case of turbulence or a stall.

One of these is the American Eagle 4184, but others include TransAsia 791 (both ATRs), Continental Airlines 1713, Air Ontario 1363, USAir 405, Comair 3272 and Sol Líneas Aéreas 5428.

While this may seem a lot compared with other causes, it should be noted that, with the exception of Sol Lineas Aereas, these accidents occurred long ago, when aircraft were less well equipped to cope with icing.

And as is often the case, icing is only one of the causes of accidents: human error is often added to the mix, as icing is an identifiable problem that pilots should be able to deal with if they detect it and are properly trained.

Bottom line

Icing is a very serious issue in air transport, and its consequences can be fatal. Fortunately, modern aircraft are equipped to cope with this, and strict procedures are followed on the ground to ensure that aircraft are properly de-iced and protected against ice before take-off.

Photo : aircraft de-icing by Jaromir Chalabala via Shutterstock

Bertrand Duperrin
Bertrand Duperrinhttp://www.duperrin.com
Compulsive traveler, present in the French #avgeek community since the late 2000s and passionate about (long) travel since his youth, Bertrand Duperrin co-founded Travel Guys with Olivier Delestre in March 2015.
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