It looks like your plane goes through a car wash, a soothing experience. The flying field operations groups deploy a large super-soaker spraying out orange or green misty fluid. You’re inside, warm and guarded from the weather. The light sound of de-icing fluid drips on the windows. Bonus points if it’s an early morning flight; it would lull you to sleep.
De-icing is a fact of flying for a lot of the United States, 9 months out of the year.
Plane de-icing is serious business for pilots and crews. Icing is a major cause for concern for flight crews and airlines from a safety and operational perspective. Airlines take every precaution to stop icing and other contamination before departure. If it’s not a clean plane, they don’t go. Southwest Airlines was forced to cancel 220 flights from Chicago Midway earlier in 2018 once they ran out of de-icing fluid. That’s a serious mistake.
Safety First: Flying Clean
“All aeroplanes are designed to fly clean,” notes the ICAO operations manual for de-icing. Clean, that is, from extraneous materials on the fuselage and lifting surfaces. The manual explains that snow, slush or ice are safety hazards which will cut back the performance of the plane dramatically. Indeed, ICAO estimates that ice on the wings comparable to coarse sandpaper will reduce wing lift by as much as half-hour and increase drag by four-hundredth. that would have a really serious negative impact on a takeoff roll.
To eliminate this type of contamination and stop it from forming during precipitation, a full army of employees is involved.
“De-icing is a careful and choreographed process requiring a good quantity of interaction between flight crews and de-icers,” said Bill Sponsler, Chief Pilot for american Airlines at Chicago – O’Hare (ORD), in an email.
De-Icing: Heated Orange Fluid
As the name suggests, de-icing is the first step in the process of removing snow, slush or ice from the fuselage, wings and management surfaces. The fluid used is propylene glycol heated to around 140-150 degrees Fahrenheit and sprayed under pressure to burst off “contaminants.” This fluid — known as type I — is mixed with water in a combination dependent on the conditions. The ratio is automatic, with de-icing trucks equipped with sensors to measure the surface conditions and modify the mixture accordingly. type I fluid is quite slippery — the de-icing trucks are usually coated in a very thin film of type I.
The teams typically spray at an angle of forty-five degrees or less to avoid directly spraying directly down on the surface. They spray the fuselage top center line, avoiding windows. They’ll then spray the wings and horizontal stabilizers from the front to the back and wing tip to wing root. (The wings are cambered, therefore spraying this manner allows the fluid to drain towards the center of the wing that saves fluid). they can additionally alter the shape of the spray, very similar to holding your thumb over a hosepipe to increase the pressure.
In colder weather and heavier snow or icing conditions, anti-icing is additionally deployed after de-icing.
Anti-Icing: green Fluid, Thicker and Not Heated
“The basic function of an anti-icing fluid is to stop frozen or freeze precipitation or expected frost adhering to the aeroplane’s cleaned or de-iced surfaces,” per ICAO guidlines.
The fluid — referred to as type IV — is more viscous than type I. this enables it to stick to the plane surface for a longer amount of time. not like type I, it’s not diluted with water.
“Think of it sort of a baby diaper,” said Gene Herrick, head of American Airlines’ de-icing operations at ORD. “The anti-ice chemicals absorb water and stop the water from sticking to the wing.”
During the procedure, the pilots will shut off the external air flow, to stop the plane (and its passengers) from suction in the chemicals. propylene glycol, that is typically used, is non-toxic. ethylene glycol, which is less commonly used, is toxic. In either case, they smell like maple syrup. (Yum!)
A common misconception, Herrick said, is that anti-icing fluid will help the plane avoid icing at cruise altitude. In fact, the bulk of it’ll have sloughed off during the takeoff roll, with all of it gone by the time the plane is 700 feet to one thousand ft higher than the ground.
At the Gate, when Pushback within the Apron or at a De-Icing Pad
De-icing and anti-icing operations happen at the gate and once pushback, or at specially-constructed de-icing pads. Gate operations are common however not always efficient. Airlines and airport operators wish to avoid having planes clogging up gates. however, most airplanes are often completely de-iced at the gate. However, if there’s ice near the forward airplanes door or the nose, de-icing takes place after pushback just prior to departure.
Many airports (such as Toronto’s Pearson airport and others in Canada) have de-icing pads. when pushing back, the pilots can taxi over to a specially constructed pad wherever multiple planes can be de-iced at the same time. At Pearson airport (YYZ), the glycol solutions are captured in tanks below the de-icing pad and recycled by chemical companies for use once more. In the US, ORD is building its own pad as a joint venture between the airport, american Airlines and United Airlines. The pad will open in Jan 2019.
How Much Time do Pilots Have after Anti-Icing?
The key concept is called “Holdover Time” — the time from spray application of anti-icing fluid till takeoff. guidelines published annually by the civil aviation authorities such as the Federal Aviation Agency in the United States include charts for every type and brand of approved de-icing and anti-icing solution. The work comes from the SAE, an industry body. (American’s Gene Herrick is on an SAE advisory board related to de-icing.)
For de-icing fluid, the holdover time typically cannot exceed twenty-two minutes, and it’s dependent on temperature and weather. De-Icing fluid is de facto solely meant to get rid of contaminants at the kickoff. Anti-icing, on the other hand, permits for extended periods between application and take-off, from as little as 9 minutes in terribly cold and snowy weather to as much as a hundred and sixty minutes. “Holdover times have inflated over the past 5 years,” Herrick said.
One determinant of holdover times appears quite old-school: visibility. On a snowy day, the control tower can determine the visibility through a visual check from the tower to markers on the field. Snow reduces visibility, however the distance they can see from the control tower interprets into an estimate of the amount of snow that’s falling. This estimate permits crews to know how much snow will build upon the wings over time and therefore an appropriate holdover time.
A more trendy approach is named “liquid water equivalent”. There, little heated pads distributed across the airport melt falling snow and measure the precise amount of precipitation. this enables anti-icing crews and pilots to more accurately determine for how long the type IV product are going to be effective.
Holdover is calculated by Herrick and his crew by means of an app, which considers the sort of aircraft (made mostly of composite materials just like the Boeing 787 and Airbus A350, or aluminium like most others), temperature, the same precipitation, and visibility. Composite aircraft have lower holdover times.
The Pilot in Command Makes the call
The Pilot in Command — the captain of the aircraft — has the ultimate say on whether or not to depart once de-icing and/or anti-icing. He or she will communicate directly with the ground employees via radio and confirm what was deployed on the craft and what the holdover time will be.
“American pilots place a great deal of trust in other employee groups to do their jobs with professionalism. Our de-ice group is no different. Our crews are very well trained, dedicated and they have a number of the most advanced instrumentation available,” said Sponsler, the chief pilot at ORD for American.
If the holdover time is exceeded and the plane has not yet departed, the captain has a choice: return for additional de-icing and anti-icing, or a visual inspection of the wings. There, the primary officer will leave the flight deck and walk down the cabin to the middle of the aircraft.
“If you do decide to conduct a cabin check, it’s all about how you present it,” Sponsler said. “The captain normally makes a relaxed public address announcement ahead of time informing the passengers that one of United States is going to be within the cabin for a moment. If you walk back to the airplane in an easygoing manner and conduct the check in a composed manner, it goes a long way in subsiding any anxious passengers.”
While de-icing and anti-icing could appear sort of a delay to departure and further time sitting on a cramped plane, it’s a vital safety feature. Next time you see it happen, enjoy the car wash and wave to the operators outside in the cold.