Wednesday, January 20, 2010

De-Ice in De-Winter

Christmas Eve and my flight ended up being an hour an a half late but hey, it wasn’t among the number of cancellations suffered at DFW because of snow. Yes, snow. Not the blizzard conditions of the East Coast or Upper Midwest mind you but the Texas kind of snow that means you can see it, it’s real but it’s really just enough to surprise some, annoy everyone else and disrupt air travel on the 2nd busiest holiday of the year.

My American Airlines flight wasn’t completely full and actually boarded on time; it was the “car wash” that held us up, something I was mentally prepared for. The “car wash” is the de-icing station, one of several set up at the far corners of the airport, to clean off any ice and snow from the airplane so it can take-off safely. “De-icing” is something of a misnomer in the technical sense of the procedure as it is really a two-part process involving both de-icing and anti-icing. De-icing first…

One thing that is obvious about snow is that it is heavy but it is not always obvious to most observers who see it piled up on to airplanes that the extra weight is not part of their take-off preparations. Every bit of snow has to come off the airplane so the pilots can see and the plane will weigh exactly as much as the planners expect it to for safe flight. Equally critical is to eliminate snow and ice build-up on the wings and “control surfaces,” the flaps and other moving parts of the wing and tail that affect movement. Not only the surfaces but also down in between the hinges and creases where frozen “precipitation” has been known to jam the controls in dangerous and deadly ways.

Extremely hot water is mixed with chemicals similar to industrial strength windshield fluid used in cars to “wash” the fuselage, wings, control surfaces and around the windows of the airplane. Workers are careful always to never spray directly in to air intake valves as the odor and smoke can cause discomfort to those inside the plane. Once the plane is considered “clean,” the second part of the treatment begins, the anti-icing.

More hot water is mixed with an even thicker solution of chemicals which some have likened to the consistency of a good Italian salad dressing. Either green or orange in color, this is applied typically only to the wings and tail control surfaces of the plane to prevent any snow or ice re-accumulation. It is also intended to remain on the plane just long enough to get to the runway and in to the air. As the plane builds up speed the solution is designed to simply peel off and leave a completely clean wing surface exposed to the air for normal flight.

In winter conditions airports and airlines know how long they have between the car wash and the runway before their application window of opportunity times out. In other words, if they send the flight to be de-iced too early, the chemicals only prevent snow and ice for so long; exceed that time window and the flight will have to go back for another wash. For this reason flights leave the gate only with a reasonable assurance of getting through the car wash and straight to the runway in as little time as possible.

Each wash, depending on the size of the plane can take from 15 to 30 minutes to complete. My flight was third in line for the procedure and then third in line again for the only runway being used for take-offs that evening from DFW, “31-Left” the northwest crosswind, a strip used 99% of the time for southbound inbound landings only. Once lined up the pilot set the brakes, opened up to full throttle and in only 22 seconds our MD-80 lifted off over the Southlake suburbs before tracking northeast and back home to Baltimore for Christmas.

We thought of the cancelled flights to Atlanta, Chicago, Los Angeles and smaller cities in Texas and considered ourselves both lucky and thankful to be an hour and a half late but still home in time for the holidays.

Gotta go.

No comments:

Post a Comment