How Does Aircraft Deicing Work?
Flying in the winter is the most challenging time of year for flight operations, even though it is widely regarded as the best time of year to fly. The air is calm and smooth; aircraft performance is unrivaled.
But on the ground, it’s a different story altogether. Winter is a brutal time of year for ground operations. It is a dangerous time of year to work on the aircraft itself, especially when snow and ice are present. It takes enormous amounts of man hours and material to keep surfaces clean and contaminant-free. And finally, it takes a lot of effort to do the actual work itself.
With that said, winter flight ops aren’t going anywhere. In fact, if anything, wintertime is one of the busiest flying seasons. The majority of America is located in areas with winter weather, so it is something that we have to learn to live with and work around. The first and most enduring answer for flight operations is aircraft de-icing. It has remained virtually unchanged for decades, is highly effective, and is the only solution that really works for aircraft deicing. So, let’s take a look at it and talk about the process.
What Is De-Icing?
This article discusses aircraft deicing, which uses deicing fluids to get frost contamination and ice buildup off of the aircraft’s surface and leading edges.
Deicing is fairly simple and is an aviation industry standard practice. When icing conditions exist, the flight crew has to do something to deal with it. The options are fairly straightforward:
- Cancel the flight
- Treat the contamination.
That’s it. There aren’t really any other options. If the flight has to proceed, and it is at freezing point, and there is ice and contamination on the leading edge, then icing fluids must be used to remove all contamination. Deicing equipment is used to apply heated ethylene glycol deicing fluid to remove contaminants.
According to NASA, heat and high-pressure hydraulic force accomplish the task of deicing aircraft. Deicing fluids are used under relatively high pressure to clean control surfaces. Deicing fluid has to be pumped with some force to achieve the desired effect, so either a mechanical pump driven by the vehicle is used, or for smaller tow-behind units, an outboard gas engine pump is installed.
This basic premise works great on smaller aircraft and commercial aircraft alike, although smaller aircraft have to be especially careful because Type I fluid (orange) has the shortest holdover time (HOT), and when it fails, it fails suddenly.
De-Icing: Heated Orange Fluid
Probably the most easily recognized deicing fluid is the infamous orange fluid. We have all seen it. However, it is not the only kind of heated deicing fluid. There are four different primary deicing fluids that are commonly used in aviation and aircraft deicers:
- Type I (red-orange)
- Type II (clear or straw-colored)
- Type III (yellow-green)
- Type IV (emerald green)
The fluid characteristics table breaks down the basic usage parameters for each type of fluid. These different types of deicing fluids are not anti-icing fluids; they are completely different, which we covered in our recent article.
The orange Type I fluid is best suited for general aviation because it will blow off or shear off at slow speeds. Here is the thing about aircraft deicer: it has to come off of the aircraft when it takes off because it also adds weight. Orange aircraft deicer fluid works on everything, but it only has an estimated protection time of roughly five to ten minutes.
It is made predominantly of propylene glycol and is best suited for GA aircraft when contaminants like falling snow have already ceased. It has no minimum rotation speed requirements so it can be used on anything, but if there is still contaminant coming down, it should be held in reserve for high-speed aircraft.
What Is Aircraft Deicer Fluid Made Of?
Aircraft deicing fluid is made from Propylene Glycol, which is a food-safe element. Modern deicing fluids are non-toxic, a good departure from yesteryear when aircraft de-icing was far less environmentally friendly. This is a net win for all of aviation and the surrounding communities.
A Brief Overview of the Plane Deicing Process
Alright, we have talked a lot about the fluids and what the process is. How about the plane deicing process itself?
Aircraft deicing removes contaminants and is applied to prevent ice for a specified duration. Propylene glycol is used at warm temperatures (around ~150° F) and sprayed on the aircraft’s surface by airport operators to remove snow and ice.
The aircraft deicing units are usually a stand-alone truck. The truck is equipped with
- The fluid reservoir, which is equipped with heating elements
- High volume pump
- The basket on a hydraulic boom
Many other options include a high-volume air pump to blast off loose contaminants like snow or slush. This feature saves ground crews a lot of expensive fluid and time.
Loose contaminants should be removed first using a special brush or shovel to pull it off of the surfaces. If it is particularly thick snow, ground crews still need to do this part of the process, but the high-volume air will usually do the trick if it is thinner.
The process usually requires 2-3 personnel:
- Truck driver
- The applicator in the basket
- Ground marshaller/safety spotter
A lot of this depends on the truck's limitations, but generally speaking, the truck will pull up to the aircraft in four areas. If you use your imagination, think about breaking the jet down into four sections:
- Front left
- Front right
- Aft left
- Aft right
Trucks can naturally pull up adjacent to those areas, and the boom usually reaches all of the aircraft’s surface that way. Loose contaminants are removed first; then, the heated fluid is sprayed at pressure, removing the rest.
It is critically important to make sure that all contaminants are removed from the aircraft; there are a number of critical penalties to aircraft function and performance if ice and other contamination are on the control surfaces.
For instance, if there is contamination near the leading edge of the tailplane, it can cause pitch upset, which could result in an uncommanded stall and also make the recovery impossible. Also, if icing or other frozen contamination is ingested into a turbine engine, it can easily FOD out the engine. That is pretty sobering: a chunk of ice can do the same damage as a bolt to a jet engine.
Furthermore, iced-over or blocked probes can cause erroneous information, leading pilots to engage or disengage systems incorrectly. Again, this can cause serious harm, so icing cannot be taken lightly. All surfaces must be thoroughly decontaminated, and engine covers should be installed immediately upon engine shutdown to prevent contamination from building up on the blades, probes, etc.
How Much Time Do Pilots Have After Anti-Icing?
The most critical phases of flight are takeoff and landing when the aircraft is low, slow, high AoA, and high power settings. Any penalties can have extremely negative consequences during the critical phases of flight.
Even just a thin layer of frost on the leading edge can push your airplane’s clean flight envelope closer to the edge of the envelope.
Why does this matter in the context of this article? Holdover times.
The FAA provides a standardized timetable for all HOT, which they release every year prior to the winter flying season.
This guidance provides the minute details on everything imaginable, but the table above really lists everything that you need to know for practical purposes.
Type II & IV both contain thickening agents to increase the viscosity of the fluid. They do this to stay on the aircraft longer to absorb and melt off snow and ice. The result is a much higher rotational speed threshold to shear off the fluid built up on the surfaces of the aircraft, but the HOT is far longer. Type II is not generally used in North America, but Type IV is common and affords the highest HOT of them all.
Where Does De-Icing Happen?
Alright, so we have a good feel for the aircraft deicing process now and what an aircraft deicer is and does. Where does this happen at the airport?
According to FAA A/C 150/5300-14D, terminal gates are acceptable for conducting aircraft deicing operations. There may be additional items that they need to add to comply with federal, state, and local regulations, but gates represent the simplest location. However, they are crowded and aren’t necessarily the best option.
Centralized Deicing Vs. Gates
A centralized aircraft deicing facility should be constructed if this is the case. Also, a central facility is a good way to keep gate delays in check. Central deicing facilities are not required, and gates or general aprons are acceptable; it all depends on the airport. Airports with low traffic counts can probably think of better infrastructure to invest in, but major hubs in wintery areas usually have centralized deicing areas.
Airports should consider centralized aircraft deicing facilities if:
- There are excessive delays or no gates available for treatment at gate facilities or
- the holdover time of applied glycols is frequently exceeded due to taxiing times to reach the departure runway or weather variations along the taxi route.
These amenities generally improve airfield traffic and allow aircraft to stage closer to the departure runway rather than being forced back to the gates. Because it is not cost-effective to create improved runoff mitigation at the terminal, several airports have constructed such facilities.
Parting Thoughts
Aircraft deicing is sometimes an afterthought, but the truth is it's one of the most critical ground support functions at an airport. Without adequate de-icing, winter flight operations will grind to a halt at many of North America’s busiest hubs.
Part of the process is to prevent icing and remove extraneous materials for the control surfaces on the aircraft. Removing snow is a big part of this so that the aircraft can fly clean with clean surfaces.
Keeping GSE up and running, or acquiring new GSE, is paramount to a smooth and efficient operation. Here at Greenwood Aerospace, we are industry experts in the procurement of GSE, including all kinds of deicing and anti-icing ground equipment. Let's talk if you are hitting dead ends trying to acquire deicing equipment. We’ll use our extensive contacts in the industry to break through and get you what you need.
At Greenwood Aerospace, we provide aerospace, military, and government procurement solutions on a domestic and global scale. We are dedicated to delivering the support you need, minimizing downtime, and providing enduring solutions for all your aerospace and facility-related necessities.
Contact Greenwood Aerospace today to discuss your aerospace and aviation needs. Or, request a quote here, and we’ll get back to you shortly.
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