Archive for de-icing delays

Air Travel, De-Icing and Delays: The Real Deal.

Posted in air travel, airline, airline delays, airline industry, airline passenger, airline pilot, airline pilot blog, airline safety, airliner, airliner take off with tags , , , , , , , , , , on March 1, 2015 by Chris Manno

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Network news media love a screaming headline, even if they have to fudge the facts to suit the rhetoric. But here is the reality behind the wailing and gnashing of teeth regarding recent ice-related delays at major airports: the airlines did a damn good job given the challenges heaped on them in this storm.

As a captain, I flew a 737 trip in the middle of the week in the slush and snow out of DFW. Here is your chance to bypass the media frenzy (NBC News carefully crafted “9 hour delay for passengers”–quietly admitting later that it wasn’t on-board) and watch the flight evolve despite the weather interference.

At 06:10, a phone call from crew schedule woke me up. I had volunteered to fly a trip that day and they offered one, a turn to John Wayne Orange County (SNA) scheduled to depart at 10:10. I agreed to fly the trip.

Normally, it takes me 35 minutes to drive to DFW. I left my house at 6:45 to allow extra time for the slush and snow snarling the highways.

I arrived at DFW an hour later, an hour and twenty minutes early. The jet was parked at the gate, had been all night in the freezing precip, so I went aboard and started powering up systems. A quick check of the wings and fuselage confirmed what I assumed driving in: we’ll need a good de-icing on the wings, control surfaces and fuselage.

Let’s get more specific about aircraft icing. First, we need to remove the accumulated ice. Second, we need to prevent more ice from re-forming on aircraft surfaces. De-icing can be accomplished by a number of different fluids under pressure. “Anti-icing” is provided by a different, specifically designed fluid that chemically inhibits the adherence of ice on aircraft surfaces.

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In our case, the ceiling was low and visibility limited by ice fog, confirming the critical temperature-dew point spread that leads to condensation which of course would freeze on any cold surface. That means both de-ice and anti-ice will be required.

Anti-ice fluid effectiveness varies with temperature, and rate and type of precipitation. The duration of anti-ice protection declines as various forms of moisture increase. So, gauging the time–called “holdover time”–is a call that must be made by the flight crew based on observation of conditions actually occurring.

You can tell when anti-ice fluid has been applied to a jet because it will be colored either brick red-ish or lime green. The intensity of the color cues the cockpit crew as to the fluids declining effectiveness–it fades as the fluid loses the ability to inhibit icing. We actually check visually that from inside the aircraft prior to takeoff.

A side note about the fluid color. Most airlines now use the green fluid because the red was difficult to distinguish from hydraulic fluid as it dripped from crevices and bays on the aircraft, sometimes several flights downline from the original de-icing treatment. I learned long ago how to differentiate the two: propylene glycol, the main ingredient in anti-icing fluid, smells and tastes sweet. Skydrol hydraulic fluid is bitter. Yes, I’ve tasted both in the thirty years (and counting) I’ve been flying jets and laugh if you want, but it saves all aboard a needless and probably lengthy maintenance delay.

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Another unseen complication that adds to the icing mix is jet fuel. The worst case is with fuel remaining in wing tanks after a flight at high altitude. The fuel in the tanks become super cold due to the temperature at altitude (often -50C or less) and as a result, the wing surfaces both upper and lower are super-chilled, causing any moisture in the air to freeze on contact. Explain that to the guy sitting next to you griping as we de-ice on a sunny, clear day: humidity plus ice-cold metal surfaces can add up to wing icing that must be removed: we can tolerate no more than 1/8″ of mere frost on the underside of the wing only. Any other airfoil contamination must be removed before flight.

Clear ice on wings is not easy to see from the cabin, particularly the area near the wing root, which is critical on aircraft with tail mounted engines like the MD-80 and -717, because upon wing flex as rotation and liftoff occur, any wing root ice that breaks loose into the slipstream could easily fly back along the fuselage to be ingested by either or both engines, with potentially disastrous results.

So why don’t aircraft have heated wing surfaces? Actually, most MD-80 upper wing surfaces do have an electrically heated thermal blanket on top of the inboard-most portion of the wing surface. But, not the curved wing root joint which is not visible from the cabin. So, you’ll notice a lot of MD-80 aircraft having to de-ice in even the slightest icing conditions.

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In our case, I knew the fuel pumped aboard for our flight would have the opposite effect. At DFW, the fuel is stored underground and pumped aboard from a hydrant, not a truck. The effect would be to warm, not freeze the wing surfaces. That would help with de-icing, but we’d still require a thorough dose of Type-2 de-icing fluid to clean ice off the jet.

By 9:10, the official crew check-in time, there was no sign of a first officer. I started the process of printing a flight release and agreeing on a fuel burn, as well as the complex process of determining takeoff speeds, made more complicated due to the presence of slush and snow on the runway. Any type of contamination, from pooled water to slush to ice can impede both acceleration and deceleration. Both maximums (takeoff and stopping) must be accurately calculated and while there is a published “runway condition,” the actual calculations are very much a realtime, eyeballs-verified assessment: I’ve broken through an undercast during an ice storm as we approached DFW only to find that just the first two-thirds of the runway had been cleared–a fact not noted on the official field report. That lopped off about four thousand feet of useable braking surface.

At 9:30, forty minutes prior to pushback, still no sign of a first officer. The roads are awful, as is the traffic, so I’m not surprised and I’m glad I left home as early as I did. I called Crew Tracking, catching them by surprise as well: in this winter storm, there were plenty of stuck, stranded or missing crewmembers. They hadn’t noticed.

I resigned myself to going out into the sleet to do the exterior inspection myself, planning to have all preflight duties complete in case the first officer should show up at the last minute. Here’s an up close look at the leading edge icing:

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and the ice on the wing trailing edge:

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Engine covers were installed, a very smart preventative measure to prevent icing, but which would require maintenance removal and documentation. I radioed maintenance to get in the cue for this required maintenance and fortunately, American Airlines had well-staffed maintenance for this shift. But again, they too had technicians who, like my F/O, were stuck in the ice storm snarled traffic, slowing things down.

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With the exterior preflight complete, I requested the upload of navigation and performance data as well as our clearances. And I took a minute to call the Crew Scheduling Manager on Duty to suggest that they grab the deadheading 737 first officer sitting in row 20 and reassign him to fly the trip. He said if the duty legality limits worked, that’s what he’d do.

By 10:00, the conscripted first officer was in the right seat, having agreed to the reassignment: he’d fly the leg to the west coast, his home base, and rather than going home, he’d also fly the leg back to DFW and only then deadhead home, if possible. Just one more crewmember going the extra mile to make the flight operation work.

We pushed back nearly on time (10:21 vs. 10:10) , but the ramp was congested with ice and slush, slowing everyone down even further. The precip had stopped, the ceiling had lifted to a thousand feet and the temperature-dew point spread had widened, all of which meant less chance of ice formation. Our holdover time would expand, allowing us to de-ice on the ramp rather than at the end of the runway. Essentially, that made for a shorter wait for all aircraft: if there is freezing precip, or any precip in freezing temps, all de-icing would have to be done at the end of the runway, meaning long takeoff delays.

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Taxiing a seventy-five ton tricycle on ice and slush is tricky, requiring slower speeds and a critical energy management: too slow and you’ll have to add excessive power to restart movement, slinging ice and slush at other aircraft. But you also need almost zero forward inertia to maintain nose gear traction in any turn, aided by asymmetric braking on the main gear into the turn. It’s a dicey operation that takes extra time.

We kept the flaps retracted on taxi-out so as to not accumulate any slush or freezing water on the underside of the flaps, a potential problem during flap retraction. Our miles-long taxi from the east side terminal to the west side runway gave us plenty of time to assess the surface conditions and fine-tune our power and speed plans.

We finally lifted off nearly fifty minutes after taxi-out. Through route shortcuts and favorable winds, we made up some of the lost time, arriving twenty-eight minutes behind schedule.

I believe my flight was more typical of all flights during an unrelenting ice storm, but mine isn’t the one craftily worded into a horror story by the media. Regardless, the fact is that icing makes flight operations complex, difficult and challenging. Yet more flight operated in the same way mine did–slow, careful, successful–than the media version of a few unfortunate cases. I take it as a compliment that the reality of these winter flights was a success story leaving the media very few flights to turn into their typically overblown horror stories.

By the time I got home nearly fourteen hours after voluntarily accepting the challenging flight assignment, the network news was already sensationalizing the “impossible” travel situation created by SnoMIGOD 2015 which dumped an unprecedented amount of snow and ice on DFW and Dallas Love Field. At least I knew the facts were not as they’d have us believe–and now you do too.

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