You may wonder what that collective groan we just heard from the back of the airplane was all about. My copilot just returned to the cockpit from his walk-around and advised that we needed to be de-iced. This was of no surprise to me, but as I picked up the PA to welcome our passengers on board and advise that we'd make a quick visit to the deice pad, a general groan filtered its way forward, like a small wave picking up energy as it traveled. I don't blame passengers for this reaction; your time is valuable, this takes time and you're anxious to be on your way. But there is some good news, we accomplish this decontamination exercise with the engines running these days which dramatically speeds up the operation. Also, do you really want to go flying in an aircraft that has snow and ice clinging to it? With a little knowledge, I'm sure that you'll arrive at the same logical conclusion that we do about this process.
This just might be my most favorite airplane photo. I love its monochromatic simplicity and grace. What do you think?
It's a nasty day out here, about ten below in blowing snow, but nice and toasty in our comfortable cockpit with a bottomless cup of delicious airline coffee. (That should spur a few comments.)
But this de-icing thing, why do we do this you may be wondering.
Is it really necessary?
Let's see if I can shed a little light on this subject. There are two terms that you'll need to know and we'll discuss them after we close the door, finish our checklists, load our weight & balance numbers and pushback from the gate.
"Ramp, Northwest 219 to push from A 68."
"219, push after the northbound Three-twenty, nose north."
"Brakes released, cleared to push after a northbound Three-twenty, nose north fellas" I instruct our pushback crew.
"Roger, cleared to push after a Three-twenty, nose north and you're cleared to start."
"Push complete, brakes set?" we hear from the push coordinator.
"Brakes set, pressures normal, cleared to disconnect, thanks for the smooth push fellas and have a good day" I say to our push crew as my FO has just completed the left engine start and reaches for the right engine start switch.
He selects "ground" on the right igniter switch, waits for max motoring N2 RPM, about 28%, places the fuel control valve on and hacks his clock. Within 120 seconds the starter motor cuts out, the generator cuts in, relieving the APU from its electrical duties and all temps and pressures should be stabilized. He'll now close APU pneumatic valves, open engine bleed valves and as soon as the APU cools, he'll shut it down. If we were dispatching with a generator inoperative, we'd leave the APU running as a back up electrical source if an engine driven generator were to fail.
And just as soon as our push crew and the airport plow have moved from our path, we'll start our taxi out.
The NWA de-ice crews do a wonderful job and are an intregal part of the operation.
We've started both engines, selected engine anti-ice on, extended our flaps, completed our "after start" and "taxi" checklists, received our taxi clearance and made our way out to the 4R De-ice pad. It's not very crowded out here this afternoon with all six slots manned and only two aircraft in front of us. We'll be out of here in no time, winging our way to SFO on our first leg of this five day trip. A clipped conversation with "iceman" that would sound heavily coded to the uninformed, lays out in detail exactly what is about to happen, as deice trucks and crews move into position. I learn that we'll de-ice first to remove existing contaminant, then anti-ice later because light snow is falling, with a specific mixture of Propylene Glycol and hot water. The coordinator will furnish me with the start and end times for this procedure so I can figure my hold over time. For the chemists among us you'll recognize this product as CH3CHOHCH2OH.
Another view of a de-ice truck approaching with an A-320 landing in the background. These folks really help keep the airline moving during inclement weather.
Close up and personal with a de-ice crew member
OK, as the first boom truck approaches, let me explain the process. We have snow and ice (contaminant) on our wings that needs to be removed, which we'll accomplish by deicing. If it weren't snowing outside, we'd then be on our way. But contaminant is falling too, light snow in this case, so we'll need to anti-ice as well which is a second spray application. This second application allows us a specific amount of time (hold over time) to taxi to the runway and depart, preventing new contaminant from sticking to our flight surfaces. If we exceed this time... yup, it's back to the deice pad, but that rarely happens.
But some meteorological conditions, such as freezing rain or freezing drizzle simply stop all operations. We can de-ice it but can't sufficiently anti-ice for it to guarantee a safe takeoff. So we don't and would wait for improved conditions. Better to get there tomorrow than make the front page of USA Today.
But why do we do all this anyway? The wing of a modern jet airplane is thin and sleek and when flaps and slats are extended, they lower our stall speed, which means we can takeoff and land at lower speeds. If these sophisticated lift surfaces are "contaminated" with snow, ice and yes, even frost, a smooth airflow over the wing is jeopardized and lift is severely impaired or destroyed, making flight questionable. Pilots don't like "questionable" so we take the time to insure flight safety and get rid of the contaminant.
An Airbus A-320
This Airbus next to us is anti-icing with a mixture of Propylene Glycol and Water. Glycol is very expensive, costing as much as $10 per gallon, so is cut with water. When heated to 150 to 180 degrees Fahrenheit and mixed as a 65/35 solution, (fluid to water) their holdover time will be in the neighborhood of twenty minutes. If the taxiways are crowded and they determine that their takeoff may be delayed longer, Iceman will adjust the mixture accordingly.
You may be wondering about our electrically actuated, pneumatically operated, wing anti-icing system. The leading edge of our wings are "plumbed" to direct hot bleed air to prevent ice build up. But this is used only in flight, has nothing to do with ground operations and on most jets is prevented from being actuated on the ground. Engine anti-ice is another matter and is used in flight and on the ground.
I just used a term you may be unfamiliar with. "Bleed air." Bleed air is hot air tapped from the engines to operate a variety of items, such as our air conditioning packs, wing anti-ice, pressurization and to rotate our engines during the start procedure. Hot air is a byproduct from a running jet engine, so we simply use it to power certain components. Nothing, not even "hot air," which there's plenty of in a commercial jet airplane, goes to waste!
These Air Tran B-717's are de-icing and as you can see by the weather conditions will be anti-icing shortly there after. As we start these procedures we announce that we'll be "shutting off the air conditioning system" by selecting the packs off. This is to avoid sucking glycol fumes into the airplane. Designed with corrosion inhibitors and wetting agents, glycol is a colorless fluid with a rather sweet odor that you may have smelled when we reactivated the air conditioning system. Due to its expense, at our hub airports, ie DTW and MSP, we vacuum the area after a spray, collect the fluid, filter and clean it and use it again. It's a good use of resources, wouldn't you agree?
Anyway, we've completed our de-icing and anti-icing procedures, have been cleared for takeoff on the Palace Three Departure and SFO is a mere four hours and 27 minutes west. Even with the delay, we'll arrive within 2 minutes of or scheduled arrival time due to light westerly winds aloft tonight. So the next time your captain comes on and advises that you'll be de-icing today and the person next to you rolls his eyes or groans just a bit, lean over and with authority teach them why this is to their benefit. There's nothing like an educated consumer!
Here's my reward the next day as we've descended on the MAGGI3 Arrival, pass over Koko Head, Diamond Head, Waikiki and line up for HNL runway 8L as Pearl Harbor slides beneath our left wing.
Bill and I have just finished day 2 of this five day trip, complete a shutdown checklist, join our flight attendants curbside and head downtown for a 28 hour layover. De-icing back in DTW seems like a long time ago as we enjoy 80 degrees at 20 degrees north latitude.
Waikiki and Diamond Head under a full moon
A little later tonight, we'll meet up with other crews who've flown in from LAX, SEA, PDX, SAN and NRT (Narita) at Dukes on Waikiki and enjoy dinner and swap tall tales beneath swaying palms and a soft Pacific breeze. But tomorrow we'll be back at it for day three of five as we fly a red eye trans-pacific east bound to LAX. I love this job! Thanks for following along and I'll see you again soon.