Here's How Dangerous Frost Really Is to a Plane, According to a Former Pilot

For some, flying can be a stress-inducing experience. After all, approximately 40 percent of the general population reports having some sort of fear of flying. Much of that apprehension comes down to not understanding how airplanes operate, especially in less-than-desirable weather conditions, including rain, wind, and, worst of all, cold temperatures that can add a layer of frost to an aircraft. But just how hazardous is frost to a flight? 

"Frost, snow, and ice adhering to an aircraft, especially the wings and tail surfaces, carry significant risk," David Cohen, the dean of the College of Aeronautics at Lynn University in Boca Raton, Florida, and also a retired Air Force colonel and command pilot, shared with Travel + Leisure. As he noted, the reason is twofold. 

"First, the shape of the wings and tail surfaces, while seemingly simple, is a result of complex calculations that aircraft manufacturers spend years developing. The wing length, curve, distance from the leading edge to the trailing edge, and the angle at which the wing is attached to the aircraft are designed for maximum efficiency for lift, reduced drag, and optimum fuel economy. The wing achieves this by having the air that passes over the top and bottom create different pressures and forces, which create lift." 

As Cohen explained, any changes to that very specific shape and size of the surface can reduce lift and increase drag, making it difficult to take off and fly. 

"This is most notable by 'contaminants' on the wing such as frost, snow, or ice. In fact, NASA studies have shown that frost as small as 80-grit sandpaper can reduce lift by 30 percent. This is because the air is no longer moving in the engineered manner over the wing, and therefore doesn’t create the lift for which the wing was designed." 

Cohen also added that the water in frost, snow, and ice carries some weight. 

"If only an inch of frost or snow was present on the wing of a Boeing 787 airliner, that would increase the weight by about 5,000 pounds," he said. "While most airliners are rarely operated at their maximum capabilities, carrying an additional 5,000 pounds of frost or snow can hinder flight. The aircraft’s performance under these conditions may not meet the expectations of engineers and flight crews."

So, once you combine that reduced lift and extra weight, "it’s clear why the FAA prohibits takeoffs with these contaminants on any aircraft unless approved deicing/anti-icing procedures are accomplished prior to takeoff."

The good news is, pilots have plenty of ways to combat these issues. Cohen noted that before takeoff, pilots physically inspect the aircraft, walking around the plane to visually examine it, looking at its general integrity, and during inclement weather, checking for ice and snow, and walking the cabin to inspect the wing surface through the window. 

"Based on these observations, along with air temperature, relative humidity, precipitation, and the weather forecast over the next couple of hours, conditions may dictate that the aircraft go through a deicing/anti-icing process prior to takeoff," said Cohen. "The decision is also influenced by pilot judgment, airline policy, and FAA requirements." 

That deicing process is likely familiar to frequent fliers who've sat on the tarmac as the heated glycol-based solution is sprayed over the aircraft surface, giving the air a distinct scent. 

"The heat helps melt whatever contamination may already be on the aircraft, and the glycol inhibits the moisture from freezing," said Cohen. "Passengers may see this process through the cabin windows as a viscous orange liquid coating the aircraft and windows."

But this needs to be done quickly, as Cohen noted, as the heated glycol may only be useful on the aircraft for 30 minutes. If the aircraft has not departed within that time frame, it may have to go back and be sprayed again. "It is not unheard of for an aircraft to be sprayed multiple times prior to departure as the pilots, ground crews, and air traffic controllers work the intricate ballet of treating aircraft and then getting them airborne in the face of reduced visibility, low clouds, and freezing precipitation," he added. 

All this said, should passengers be worried about frost?

"There is a tongue-in-cheek saying about air travel: 'Time to spare? Go by air!' In 2023, U.S. airlines scheduled more than 600,000 flights. Less than 1.5 percent were canceled, and more than 78 percent of the flights that flew arrived within 15 minutes of their scheduled time.

"That’s pretty remarkable when you think about the volume of equipment, people, technology, and uncontrollable weather involved," said Cohen. "This isn’t to say there isn’t room for improvement, but my point is that passengers should worry less about frost or winter conditions. Instead, they should prepare to exercise patience and understanding, knowing the airline, aircrew, and everyone supporting their journey would never put them in harm's way. Missing a family event due to a canceled or delayed flight may certainly cause frustration and anxiety for a passenger, but they should be comforted by the fact that their safety will never be compromised for a schedule or the bottom line by the professionals entrusted to get them to their destination."