MINNEAPOLIS (WCCO) — This Thanksgiving holiday, Mother Nature apparently didn’t consult the calendar.

Wednesday will be one of the busiest travel days of the year. That makes for particularly bad timing because a Nor’easter capable of dropping many as 13 inches along the East Coast is set to hit Wednesday morning.

Millions of people will be affected by the storm. Thousands of flights are already delayed and some are pre-preemptively cancelled.

So, when can planes fly in bad weather?

“As long as the aircraft has braking action on that runway that they’re able to stop that aircraft,” said Gregory Zahornacky, a former USAirways pilot and assistant professor of aeronautical science at Embry-Riddle Aeronautical University.

Each plane manufacturer and airline has very specific rules on when it’s safe to fly with wind, snow, visibility and rain.

Zahornacky says pilots are especially cautious when it comes to thunderstorms and freezing rain.

Once the plane is in the air, it can de-ice itself. But on the ground, freezing rain is hard to discern, adding weight to a plane and affecting the aerodynamics of the wings.

But Zahornacky says pilots will still take off in freezing rain under certain conditions.

“As long as they’re able to clear that off the aircraft, and as long as the ground operations are not impeded by the freezing rain on the surface because if there’s no braking action, you can’t go anywhere,” he said.

Crosswinds can cause problems for pilots. Every aircraft has a maximum that generally falls between 25 and 29 knots for larger planes in clear conditions.

A couple of inches of snow are generally not a problem as long as crews can remove it from the aircraft. Clean surfaces are a requirement before a plane allowed to depart. But blizzards can cause huge headaches as crews must close runways to plow them.

“Your problem is not so much keeping the aircraft clear of the snow itself off the aircraft,” Zahornacky said. “It’s going to be that of the air traffic, because there are going to be so many delays that you have snow accumulate on the wings.”

The de-icing solution only lasts so long, and closing the runways to plow steals those minutes.

Heather Brown

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