Winter weather flying:
How do they do that?

by Michele Regenold

On Jan. 13, 1982, Air Florida Flight 90 crashed into a Washington, D. C. bridge and plunged into the ice-covered Potomac River. The crash killed 74 of the 79 people aboard (passengers and crew) and four people on the ground. The Boeing 737 had just taken off from Washington National Airport in Washington, D. C. on its way to Ft. Lauderdale, Florida.

A heavy snowfall that day temporarily closed the airport and delayed Flight 90’s departure by nearly two hours. Thousands of planes fly in weather just as bad every year. They take off, fly to their destinations, and land safely. How do they do it? And what went wrong for Flight 90?

Before takeoff

In winter, before a passenger jet takes off, the second officer walks around the plane to check for ice on the wings and reports it to the captain. The captain calls the airline to deice the plane. When the weather’s bad enough, the airlines automatically deice all their planes.

The deicing process is simple. A member of the airline’s ground crew sprays the plane with a liquid deicing solution. It’s sprayed on hot, under high pressure to melt ice and snow.

The deicing fluid contains about 90% glycol and 8% water. Glycol is an alcohol that lowers the freezing point of water from 32 degrees Fahrenheit to -58 degrees Fahrenheit. It’s similar to the antifreeze used in cars.

Planes that sit for less than 15 minutes before takeoff get deiced and they’re done. Planes that have to wait longer before takeoff follow a two-step process. First, they get deiced. Then they get sprayed with an unheated anti-icing fluid. This fluid has a gluey quality that helps it stay on the plane and prevents additional ice from forming (anti-icing prevents and deicing removes).

Retired Northwest Airlines Capt. Jerry Gilliand says that at the first sign of weather that may cause ice (anytime it's 50 degrees Fahrenheit or colder and visible moisture is present), a jumbo jet pilot turns on engine anti-icing. Hot air from the jet engines runs through tubing inside the wings. The hot air heats the wings enough to prevent ice from forming and melt any that may have already formed. Engine anti-icing also keeps sensors working properly and giving accurate instrument readings. The captain may turn on engine anti-icing anytime it's needed, whether the plane is on the ground or in the air.

Airborne

“Jumbo jets can fly through just about all winter weather,” Gilliand says. He worked for Northwest for 33 years and flew DC-10s. “You can take off in a blizzard as long as you have some forward visibility and can see the center line lights or markings.”

When a jumbo jet is in the air, traveling at 600 mph, snow blows right over the wings. It’s not a concern. But ice is another story.

When a plane is in the air, ice can form on it rapidly. If as little as half an inch of ice builds up on the wings, it changes the shape of the wing. The change in shape means that air no longer glides smoothly over and under the wing. That reduces lift. Without enough lift, it’s hard to keep the plane aloft.

Smaller planes with propellers don’t have the heat from a jet engine to warm the wings. Instead, many small planes have what are called deicing boots. They inflate to knock off ice from the leading edge of the wings. Sometimes they don’t remove all the ice, which makes flying a little trickier. The propeller, however, has an electric deicer that heats the blades.

Pilots of all sizes of aircraft say that if icing issues are taken care of, winter flying is great. Cold air is denser than warm air, so engines perform better. In warmer weather, air turbulence can upset stomachs and make jittery passengers even more nervous. In winter, the air is smooth.

Landing

For landing, visibility is critical, Gilliand says. If it’s snowing, raining, or sleeting hard and visibility is at or near the minimum, pilots of large jets have only a few seconds from the time they see the runway to the time they land.

The co-pilot watches the instruments to make sure the autopilot (a system to control navigation) is working correctly. As the plane makes its final approach, the autopilot is flying. The captain monitors the instruments until the aircraft gets near the visibility minimums. Then the captain looks for the runway lights. If the lights are in sight, and the aircraft is at or above minimums, the captain disconnects the autopilot and manually lands the plane. If not, the captain does not land and instead follows procedures for a missed approach.

Usually a single person monitors instruments and the runway and lands the plane. The captain and co-pilot take turns. New jets (747s, 757s, and 767s) can be programmed to land themselves.

Clean runway is crucial

Ice on the runway isn’t as serious as ice on the wings Capt. Gilliand says. But it’s still a major safety concern.

On Dec. 8, 2005, a Southwest Airlines jet slid off the end of a slippery runway at Chicago’s Midway Airport. The plane skidded through a fence and onto a street where it crashed into a minivan. A boy in the van was killed. It was lightly snowing that day.

Keeping a runway clean and clear can be tough. At the Des Moines International Airport, the goal is to clean the runways in 30 minutes or less. Sometimes that means running plows in a conga line down the runway. Sometimes they have to turn right around and plow the area they just plowed again.

Plows used at large commercial airports usually have wider blades than plows used on roads. Since runways are wider than roads, the extra wide plows help get the work done faster.

Airport maintenance crews also operate blowers that can shoot snow many feet away, well beyond the signs and lights that pilots need to see along the runway and taxi areas. For light, dry snow, crews drive sweepers or brooms.

In Des Moines, the airport operates only one runway when the winter weather is bad (the main north-south runway because the wind is frequently out of the north). This runway has temperature sensors embedded in the pavement. When the pavement gets close to freezing, the maintenance crew sprays on a liquid anti-icing solution to help prevent ice from forming on the runway.

Airports often use liquid anti-icing instead of sand or salt. The problem with sand and salt is that they stay on the pavement after the ice and snow are melted.

On a runway, that’s bad news because the grit might be sucked up into an engine and cause problems, says Shawn Arena, deputy aviation director for operations and maintenance for the Des Moines International Airport. For example, an F-16 jet’s air intake is “like a vacuum cleaner,” Arena says. So the runway must be very clean.

A clean, dry runway also provides the best friction between the concrete pavement and the wheels of an aircraft. (Friction is the resistance of the wheels rolling over the pavement.) After the Des Moines airport crew removes snow, they test the runway’s friction. They drive an SUV down the runway and slam on the brakes. The SUV has a special meter on it that measures the friction.

Snowy or icy pavements are slippery, of course, which means there’s less friction. Less friction means it’s harder to stop.

If a runway is icy, the pilot of a jumbo jet will switch the engine to reverse thrust and use the brakes at the same time. Usually it’s reverse thrust, then brakes. The engine roar a passenger hears right after touching down is the engine in reverse.

Jumbo jets have anti-skid brakes. If wheels start to slide, the brakes automatically release and then reapply, like a car’s anti-lock brakes. Once the jet slows to 80 knots (about 92 miles per hour), the pilot uses only the brakes.

There’s no question that ice and snow can make flying dangerous. But when flight crews, airline ground crews, and airport maintenance staff do their jobs properly, flying can be smooth and safe.

About the jobs

Airline pilot

Do you love to fly? Most pilots have a passion for flying. You also need to be detail-oriented and concerned about the safety of your passengers and crew. Most of all you need flying experience. Learn more about how to become an airline pilot: http://travel.howstuffworks.com/pilot.htm.

Basic requirements/qualifications

You can take lessons to earn a private pilot’s license when you’re 16, although you need to be 17 to get the license. To be an airline pilot, you need a commercial pilot certificate, which you earn after attending commercial pilot ground school and logging 250 hours of flight time. You may also need special ratings, like multi-engine and instrument. Many airlines require that pilots have a bachelor’s degree.

You can take private lessons or train at a technical or community college such as Indian Hills Community College in Ottumwa, Iowa, or Iowa Central Community College in Webster City, Iowa. Learn more about these colleges’ flight training programs:

• Indian Hills Community College
• Iowa Central Community College

Airport field maintenance staff

In the winter, you’ll do mainly snowplowing and related activities. In warmer weather, you’ll do construction, mowing, and other activities related to airport maintenance.

Basic requirements/qualifications

• You need to be able to read and write English.
• You need at least a high school diploma. A two- or four-year degree is helpful if you want to move up the career ladder. You’ll get regular training in-house.
• An interest in aviation is helpful.
• You also need to be highly safety conscious.
• You should be willing to learn to operate lots of different equipment.

Author's note: Dean Regenold is my dad. He's an adventurer and a bit of a risk taker, so I knew he'd have at least one good story to tell about winter flying. MR

A scary winter flying story

One cold winter night, Dean Regenold, a charter pilot with 35 years of experience, hunched inside his coat and trudged out to the twin-engine Cessna 310. He started the plane and let it idle a few minutes, just long enough to warm up the engine. Then he shut it down and headed back inside the terminal to wait.

His boss and four other passengers were late. It was nearly 6:00 p.m. They’d been scheduled to leave at 4:00.

While Regenold waited, the weather turned colder, hovering around 0 degrees Fahrenheit. A foot of snow lay on the ground.

"The right engine blew oil all over the windshield."

Every 30 minutes, Regenold went out to start the plane. His “super cheap” boss had asked him to do that instead of having the airport crew preheat the plane before take-off because the preheating service cost extra.

Finally, around 8:30, five large, chatty men arrived with too much luggage.

Everyone climbed aboard. Their luggage was crammed behind the third row of seats (the plane had six seats in all). The passengers laughed and talked.

They took off. As the plane climbed through layers of clouds, ice formed on the leading edge of the wings.

As they flew through 5,000 feet on their way to 6,000 feet, “the right engine blew oil all over the windshield,” Regenold said.

Meanwhile the wings were continuing to ice up.

The chatty passengers went quiet. The right engine was dead. Snow had clogged the right oil vent.

Each time Regenold had started the plane while waiting for his passengers, the propeller blades were likely picking up snow and throwing it into the right engine nacelle (the engine housing).

He immediately feathered the right engine so the propeller was perpendicular to the airflow and would create less drag. Meanwhile the wings were continuing to ice up and the deicing boots weren’t breaking it all off.

Should they turn around or keep going?

Regenold decided to keep going. The weather was slightly better at their destination, Coffeyville, Kansas. Plus the airport was an old Air Force training base and had a very long runway.

To compensate for the icy wings and the single engine, Regenold had to approach the runway at 20 knots, quite a bit above normal speed. He needed a lot of runway to slow down.

“We landed with a thud,” he said. Scared but safe.