Almost as soon as we were through 10,000 feet, I had my atlas out. It was completely clear along our route - a rarity in November - and on the dark, moonless night, every light for hundreds of miles was visible. Every town and road printed on the map was duplicated in orange and white pixels below. From Memphis we headed northeastwards on J42, toward Nashville. It grew steadily brighter until we passed overhead; then the glow of suburbia quickly gave way to the isolated pinpricks of eastern Kentucky's rural hill country. Louisville floated by to our left; to our right, Knoxville illuminated the spine of the Great Smokey Mountains. My First Officer broke the silence to point out his hometown where Tennessee, Kentucky, and Virginia all come together. At Beckley, WV, we made a slight right to cross the Ridge-and-Valley Appalachians just north of I-64. A thin band of light stretching as far as the eye could see marked the Great Valley; the dark band after that, the Blue Ridge. We reentered "civilization" over Charlottesville, VA, the pixels becoming ever thicker and brighter as we approached Washington DC. From 35,000 feet, we could clearly make out the dark National Mall and the floodlit Capitol Building. As we passed over Chesapeake Bay into Delaware, I noted how Washington, Baltimore, Philadelphia, Newark, and New York essentially form one contiguous, enormous metropolis. The Jersey shore, to our right, was much darker but the casinos of Atlantic City shone brightly, prompting my FO to reminisce about his freight dog days flying into ACY. Now New York's glow, visible 200 miles prior, hardened and formed into city and water, then the individual boroughs, and then mile after mile of individual streets and buildings. I picked out the Empire State and Chrysler Buildings as we overflew JFK and LGA. At the Connecticut coast we turned right; the moonless night and dark waters of Long Island Sound made me think of JFK, Jr. By now we were on our descent; the arrival took us over Providence, RI, which until then had always been a fuzzy spot in my geographical knowledge. We went "feet wet" above the spot that the Pilgrims went "feet dry." The vectors to final took us far out over the Atlantic, almost to the tip of Cape Cod. Our 150 minute night tour of the east coast concluded with a nice view of the Boston skyline from the final approach to runway 27.
Prior to flying for NewCo, I had spent very little time "out east." In fact, the furthest east I'd flown was Grand Rapids, MI, and that was on a cross-country flight I did in college! My subsequent flight instructing, freight dogging, and airline flying was all on the west coast. At Horizon, the easternmost destination for the Q400 was Billings, MT. At NewCo, the majority of our destinations are east of the Mississippi. On the east coast proper, we fly to MHT, BOS, JFK, LGA, EWR, PHL, BWI, IAD, RIC, ORF, CLT, JAX, and MCO. When I began flying to these places, my geographic knowledge was sorely lacking. Now all the pieces are starting to fit together.
When I was flying out west, I had no idea just how good I had it. Flying on the east coast in a royal pain. Out west, it's Direct-To everywhere and talk to ATC once every 20 minutes to change frequencies. Out east, it's nonstop convoluted reroutes, last-minute crossing altitude restrictions, and an endless litany of frequency changes. You eventually give up even trying to check in with certain sectors after having your check in stepped on half a dozen times. Airports like PHL, EWR, LGA, and JFK are delay-prone on good days; throw in some bad weather and you're going nowhere quick. Those airports make me thankful that our turd of a contract at least has "Block or Better" pay.* Our hotels at eastern layovers tend to be in decrepit industrial areas near the airport, and the shuttle van drivers are often surly and hurried.
Despite all that, I still enjoy going east. I guess the novelty just hasn't worn off yet. I enjoy the aerial sightseeing when the weather cooperates. The Appalachians, Catskills, and Adirondacks, while less starkly grand than the Rockies, Sierras, and Cascades, have great natural beauty of their own. The human geography, too, is interesting to me: the patchwork quilt-like farmsteads of rural areas, the little towns secluded in dead-end valleys miles from anywhere, the seemingly endless cities of the BosWash corridor. There's a lot of history out east; I enjoy having a birds-eye view of the landscape that famous battles and campaigns were waged across.
On the ground, there's a lot to do if you make the effort. I haven't spent much time in most of the cities we go to, so they invite exploration. The morning after my sightseeing flight up the eastern seaboard, I woke up early and hopped on the subway to downtown Boston. I reemerged at Boston Common, America's oldest park, and started following the red brick path of the Freedom Trail. It was fascinating to see so many important historical sites in the course of a fairly short stroll. The South Meeting House, the Old State House, Old North Church, and Bunker Hill are all legendary places I've heard about since grade school but have never seen for myself. Walking in and around them made the history seem more real, more palpable; I felt new appreciation for the vision and courage of men like Joseph Warren, Samuel Adams, and Paul Revere.
I have a long Philadelphia layover coming up soon. I hope to make it to the Revolution-era sights there. If they're anywhere nearly as interesting as the Freedom Trail in Boston, it should take some of the sting out of having to operate out of PHL.
*"Block or Better" means that we are paid the greater of scheduled or actual block time. Therefore, when we're delayed we get paid extra, but we don't get shorted for being early. Although Horizon has a much better contract than NewCo, they did not have Block or Better; I got paid based only on the historical block time for the leg (usually less than scheduled block), with no additional compensation for overblocking. If Horizon flew into JFK, LGA, or PHL, that'd be a very bad thing to have in the contract.
Sunday, November 30, 2008
Friday, November 21, 2008
The Iceman Cometh
Well, there's no escaping it now. Minnesota has had several days of snow, although none of it lasted more than a few hours; it's currently 12 degrees in Minneapolis. When I got done with a trip yesterday morning, my short walk from the bus stop to our apartment froze my fingers and ears so thoroughly that I didn't venture outside again all day. My six month hibernation begins now.
If I could spend the entire winter curled up inside with a warm blanket and hot chocolate I very possibly would, but alas, the need to earn a living saves me from being a total recluse during winter. Being a pilot is a good job for someone who hates long cold winters but lives in Minnesota, as it gets me above the clouds into sunshine rather frequently and also involves the occasional layover in Phoenix or San Antonio. Unfortunately two of RedCo's three hubs are in northern states, so I do spend a lot of time operating in wintry conditions. This rather frequently involves deicing. I deiced for the first time of the season about a month ago. Given that I hadn't done it since last winter, I took that as my cue to open our Deicing/Anti-icing manual and study up.
As I mentioned in my last post, anti-icing systems on jets are beautifully effective in flight but provide no protection on the ground. For that, we use propylene glycol-based deicing fluids somewhat similar to the antifreeze fluid used in your car. Similar fluids have been used in aviation for quite a while, but for a long time they were poorly understood and their use was nonstandard throughout the industry. After some notable accidents involving airliners attempting takeoff with iced-up wings, the FAA got serious about ground deicing. Now every Part 121 carrier is required to maintain and distribute an FAA-approved Ground Deicing/Anti-icing Manual. It spells out in great detail the various ground and flight crew roles and responsibilities, what parts of the aircraft must be "clean" for takeoff, approved methods of removing contamination, the limitations of various anti-ice fluids, and the checks that must be accomplished before an airplane may take off.
As the name of the manual suggests, there are two stages to ground deicing/anti-icing. Deicing is intended to remove any previously accumulated contaminants that are adhering to the airframe. This may include frost, freezing rain, snow, or airframe ice from the last flight. Anti-icing prevents further accumulation of freezing precipitation between deicing and takeoff. In very mild conditions, both of these steps may be accomplished in a single application of deicing fluid, but more often the steps are accomplished with separate coats of different fluids.
The deice fluid used to remove previous contaminants is called Type I fluid. It is fairly thin, slippery, and is dyed red to help deicing personnel see which parts of the aircraft have already been sprayed. Type I fluid is normally heated between 130 and 180 degrees F, and is sprayed out at considerable pressure to aid in knocking contaminants off the airframe. As Type I fluid isn't very viscous, it doesn't adhere to the airframe well. It also has a somewhat limited ability to absorb moisture. For both of these reasons, Type I fluid is used for anti-icing purposes only for short periods or in very light ground icing conditions.
The more commonly used anti-ice fluid is called Type IV. It has thickening agents added and is dyed green. Type IV is always applied cold after a previous application of Type I fluid. It is sometimes diluted with water, not only to save costs but also to (rather counter-intuitively) lower its freezing point. A solution of 75% fluid and 25% water has a freezing point of around -55C; undiluted fluid has around the same -30C freezing point as a 50-50 mix. Type IV fluid's greater viscosity helps it to better adhere to the airframe. It is designed to shear off at around 100 knots airspeed on the takeoff roll, leaving a clean wing. It also has greater moisture absorption capabilities than Type I fluid. All this means that it protects the airframe against contamination for much longer periods than Type I fluid.
The most common apparatus used to spray deicing fluid is a boom truck. The truck drives around the aircraft while the deicer sprays the fluid from a basket on top of the boom. Both Type I and Type IV fluid can be and often are sprayed from the same truck in subsequent applications. A fairly recent development is infrared deicing. Infrared deicers melt existing snow and ice off the airframe as the plane taxies through a hangar-like structure. This arrangement still requires a truck to spray Type IV fluid for anti-ice protection. There are only a few infrared deice installations in the US.
Occasionally ground crews will deice aircraft before the flight crew arrives in the morning if there was frost or snow accumulation overnight but ground icing no longer exists. Usually, though, crews must request deicing. At small stations, the ground crew needs advance warning to make sure the truck has enough fluid and to heat it up. If there are any contaminants adhering to the airframe, or if there's steady snowfall, the decision to deice is an easy one. It's less clear when the temperatures are just warm enough that the snow is melting on contact, or if flurries aren't quite sticking to the airframe. You don't want to deice unnecessarily due to the time and cost involved, but you also don't want changing conditions to make you come back for deicing at the last minute either.
At outstations, I'll inform operations or a member of the ground crew that we need to deice at least 30 minutes before departure. At most of these airports, we get deiced right after pushback from our gate, before we've started our engines. At the smallest stations, the same rampers that just loaded the bags and pushed us back will then hop in the deice truck. At large northern outstations and hub airports, there are dedicated deice pads located near the end of the runways and manned by a virtual army of trucks and staff during winter weather. At Minneapolis, there are four deice pads that can each handle half a dozen aircraft simultaneously! The usual drill is to call "The Iceman," or central coordinator, as soon as you know you'll need deicing. They'll either assign you a pad or dispatch a truck to deice you near the gate when you push back. If assigned a pad, you confirm it with the Iceman when you begin taxiing and then contact that pad on a discrete frequency to be assigned a lane. You usually deice with engines running at deice pads.
Before the crew begins deicing, the deice coordinator will plug into the ground intercom or transmit via radio to confirm what type of fluid we want and that we are configured for deice. This involves ensuring the flaps are retracted, the stabilizer trim is full nose-down (to prevent fluid from entering internal mechanisms), and turning off all the bleed and pack switches. This last step is especially important to prevent passengers from breathing atomized glycol. Unlike ethylene glycol (antifreeze), propylene glycol is supposed to be fairly non-toxic - but it's not exactly pleasant to inhale, either. After deicing is complete, we wait a full minute before selecting bleed sources on, and another minute after that before turning the packs back on.
Once the process is complete, the deice coordinator will tell us the type and amount of fluid used, the fluid/water mixture and freezing point, and the time that fluid application began. The last bit of information is especially important, for it is the time that our holdover time is calculated from. Holdover time is the length of time that the fluid can be expected to provide anti-ice protection in active ground icing conditions. It varies by type and mix of fluid, type and intensity of precipitation, outside air temperature, and a few other factors. We use a series of tables to calculate our holdover time for the given conditions. The tables give us a range of times; for example, with moderate snowfall at a temperature of -5C, Type I fluid has a holdover time of five to eight minutes and undiluted Type IV has a holdover time of 20 to 40 minutes. The Captain chooses a holdover time within this range that most closely corresponds to prevailing conditions, and may adjust the time upward or downward in response to changing conditions. The holdover time begins when the application of the last coat of anti-ice fluid begins; takeoff must be commenced before the holdover time expires.
Of course, in any weather that makes holdover time a factor, there are likely air traffic delays that may hinder a timely takeoff. ATC is usually pretty good about asking pilots their holdover expiration and resequencing aircraft if necessary. Sometimes best efforts aren't enough and the holdover time expires. Different airlines handle this in different ways. Some require the aircraft to return for secondary deicing. Others, including NewCo, permit the use of a Pre-Takeoff Contamination Check. This is a tactile exterior inspection conducted by trained deicing personnel to confirm that the aircraft is still clean and the fluid has not failed. If the aircraft passes this check, it is still allowed to take off so long as the takeoff happens within five minutes of the check. Close coordination between the crew and operations is necessary to ensure there are personnel available at the end of the runway in case holdover time expires.
In any case, shortly before takeoff the flight crew must perform their own Pre-Takeoff Check to ensure the fluid has not become saturated with moisture. Basically you just look at the few airframe parts visible from the cockpit and observe the sheen of the fluid. If it is dull and milky, the fluid has failed and the aircraft must be deiced again. If it's still glossy, then you're set to go. Hopefully you're headed South where you can thaw a bit. Unless they're having a cold snap, that is; the only thing worse than winter weather in the North is winter weather in the South! While Minneapolis and Detroit are true pros at fast, effective deicing, the same is decidedly not true of places that only see winter weather once or twice a year. They simply aren't equipped or staffed for it, and there's always a learning curve.
Portland is one notable exception. They're blessed with fairly mild winter weather but when they do get it, it's in the form of truly nasty ice storms. Accordingly, Horizon puts heavy emphasis on training and equipping their PDX deicing crews for those days. In the end, it's usually all for naught; they soldier on for a few hours before freezing rain closes the airport entirely and grounds a large portion of Horizon's fleet. A few years ago a friend of mine was the FO on the last flight that landed before a particularly nasty ice storm closed PDX for several days. In the last few minutes of the flight, they encountered heavy freezing rain; by the time they landed, every inch of the airframe was encrusted in several inches of ice! The deicing team's last act before conceding to Mother Nature was to deice my friend's CRJ so they could get the main cabin door open to deplane the passengers.
If I could spend the entire winter curled up inside with a warm blanket and hot chocolate I very possibly would, but alas, the need to earn a living saves me from being a total recluse during winter. Being a pilot is a good job for someone who hates long cold winters but lives in Minnesota, as it gets me above the clouds into sunshine rather frequently and also involves the occasional layover in Phoenix or San Antonio. Unfortunately two of RedCo's three hubs are in northern states, so I do spend a lot of time operating in wintry conditions. This rather frequently involves deicing. I deiced for the first time of the season about a month ago. Given that I hadn't done it since last winter, I took that as my cue to open our Deicing/Anti-icing manual and study up.
As I mentioned in my last post, anti-icing systems on jets are beautifully effective in flight but provide no protection on the ground. For that, we use propylene glycol-based deicing fluids somewhat similar to the antifreeze fluid used in your car. Similar fluids have been used in aviation for quite a while, but for a long time they were poorly understood and their use was nonstandard throughout the industry. After some notable accidents involving airliners attempting takeoff with iced-up wings, the FAA got serious about ground deicing. Now every Part 121 carrier is required to maintain and distribute an FAA-approved Ground Deicing/Anti-icing Manual. It spells out in great detail the various ground and flight crew roles and responsibilities, what parts of the aircraft must be "clean" for takeoff, approved methods of removing contamination, the limitations of various anti-ice fluids, and the checks that must be accomplished before an airplane may take off.
As the name of the manual suggests, there are two stages to ground deicing/anti-icing. Deicing is intended to remove any previously accumulated contaminants that are adhering to the airframe. This may include frost, freezing rain, snow, or airframe ice from the last flight. Anti-icing prevents further accumulation of freezing precipitation between deicing and takeoff. In very mild conditions, both of these steps may be accomplished in a single application of deicing fluid, but more often the steps are accomplished with separate coats of different fluids.
The deice fluid used to remove previous contaminants is called Type I fluid. It is fairly thin, slippery, and is dyed red to help deicing personnel see which parts of the aircraft have already been sprayed. Type I fluid is normally heated between 130 and 180 degrees F, and is sprayed out at considerable pressure to aid in knocking contaminants off the airframe. As Type I fluid isn't very viscous, it doesn't adhere to the airframe well. It also has a somewhat limited ability to absorb moisture. For both of these reasons, Type I fluid is used for anti-icing purposes only for short periods or in very light ground icing conditions.
The more commonly used anti-ice fluid is called Type IV. It has thickening agents added and is dyed green. Type IV is always applied cold after a previous application of Type I fluid. It is sometimes diluted with water, not only to save costs but also to (rather counter-intuitively) lower its freezing point. A solution of 75% fluid and 25% water has a freezing point of around -55C; undiluted fluid has around the same -30C freezing point as a 50-50 mix. Type IV fluid's greater viscosity helps it to better adhere to the airframe. It is designed to shear off at around 100 knots airspeed on the takeoff roll, leaving a clean wing. It also has greater moisture absorption capabilities than Type I fluid. All this means that it protects the airframe against contamination for much longer periods than Type I fluid.
The most common apparatus used to spray deicing fluid is a boom truck. The truck drives around the aircraft while the deicer sprays the fluid from a basket on top of the boom. Both Type I and Type IV fluid can be and often are sprayed from the same truck in subsequent applications. A fairly recent development is infrared deicing. Infrared deicers melt existing snow and ice off the airframe as the plane taxies through a hangar-like structure. This arrangement still requires a truck to spray Type IV fluid for anti-ice protection. There are only a few infrared deice installations in the US.
Occasionally ground crews will deice aircraft before the flight crew arrives in the morning if there was frost or snow accumulation overnight but ground icing no longer exists. Usually, though, crews must request deicing. At small stations, the ground crew needs advance warning to make sure the truck has enough fluid and to heat it up. If there are any contaminants adhering to the airframe, or if there's steady snowfall, the decision to deice is an easy one. It's less clear when the temperatures are just warm enough that the snow is melting on contact, or if flurries aren't quite sticking to the airframe. You don't want to deice unnecessarily due to the time and cost involved, but you also don't want changing conditions to make you come back for deicing at the last minute either.
At outstations, I'll inform operations or a member of the ground crew that we need to deice at least 30 minutes before departure. At most of these airports, we get deiced right after pushback from our gate, before we've started our engines. At the smallest stations, the same rampers that just loaded the bags and pushed us back will then hop in the deice truck. At large northern outstations and hub airports, there are dedicated deice pads located near the end of the runways and manned by a virtual army of trucks and staff during winter weather. At Minneapolis, there are four deice pads that can each handle half a dozen aircraft simultaneously! The usual drill is to call "The Iceman," or central coordinator, as soon as you know you'll need deicing. They'll either assign you a pad or dispatch a truck to deice you near the gate when you push back. If assigned a pad, you confirm it with the Iceman when you begin taxiing and then contact that pad on a discrete frequency to be assigned a lane. You usually deice with engines running at deice pads.
Before the crew begins deicing, the deice coordinator will plug into the ground intercom or transmit via radio to confirm what type of fluid we want and that we are configured for deice. This involves ensuring the flaps are retracted, the stabilizer trim is full nose-down (to prevent fluid from entering internal mechanisms), and turning off all the bleed and pack switches. This last step is especially important to prevent passengers from breathing atomized glycol. Unlike ethylene glycol (antifreeze), propylene glycol is supposed to be fairly non-toxic - but it's not exactly pleasant to inhale, either. After deicing is complete, we wait a full minute before selecting bleed sources on, and another minute after that before turning the packs back on.
Once the process is complete, the deice coordinator will tell us the type and amount of fluid used, the fluid/water mixture and freezing point, and the time that fluid application began. The last bit of information is especially important, for it is the time that our holdover time is calculated from. Holdover time is the length of time that the fluid can be expected to provide anti-ice protection in active ground icing conditions. It varies by type and mix of fluid, type and intensity of precipitation, outside air temperature, and a few other factors. We use a series of tables to calculate our holdover time for the given conditions. The tables give us a range of times; for example, with moderate snowfall at a temperature of -5C, Type I fluid has a holdover time of five to eight minutes and undiluted Type IV has a holdover time of 20 to 40 minutes. The Captain chooses a holdover time within this range that most closely corresponds to prevailing conditions, and may adjust the time upward or downward in response to changing conditions. The holdover time begins when the application of the last coat of anti-ice fluid begins; takeoff must be commenced before the holdover time expires.
Of course, in any weather that makes holdover time a factor, there are likely air traffic delays that may hinder a timely takeoff. ATC is usually pretty good about asking pilots their holdover expiration and resequencing aircraft if necessary. Sometimes best efforts aren't enough and the holdover time expires. Different airlines handle this in different ways. Some require the aircraft to return for secondary deicing. Others, including NewCo, permit the use of a Pre-Takeoff Contamination Check. This is a tactile exterior inspection conducted by trained deicing personnel to confirm that the aircraft is still clean and the fluid has not failed. If the aircraft passes this check, it is still allowed to take off so long as the takeoff happens within five minutes of the check. Close coordination between the crew and operations is necessary to ensure there are personnel available at the end of the runway in case holdover time expires.
In any case, shortly before takeoff the flight crew must perform their own Pre-Takeoff Check to ensure the fluid has not become saturated with moisture. Basically you just look at the few airframe parts visible from the cockpit and observe the sheen of the fluid. If it is dull and milky, the fluid has failed and the aircraft must be deiced again. If it's still glossy, then you're set to go. Hopefully you're headed South where you can thaw a bit. Unless they're having a cold snap, that is; the only thing worse than winter weather in the North is winter weather in the South! While Minneapolis and Detroit are true pros at fast, effective deicing, the same is decidedly not true of places that only see winter weather once or twice a year. They simply aren't equipped or staffed for it, and there's always a learning curve.
Portland is one notable exception. They're blessed with fairly mild winter weather but when they do get it, it's in the form of truly nasty ice storms. Accordingly, Horizon puts heavy emphasis on training and equipping their PDX deicing crews for those days. In the end, it's usually all for naught; they soldier on for a few hours before freezing rain closes the airport entirely and grounds a large portion of Horizon's fleet. A few years ago a friend of mine was the FO on the last flight that landed before a particularly nasty ice storm closed PDX for several days. In the last few minutes of the flight, they encountered heavy freezing rain; by the time they landed, every inch of the airframe was encrusted in several inches of ice! The deicing team's last act before conceding to Mother Nature was to deice my friend's CRJ so they could get the main cabin door open to deplane the passengers.
Thursday, November 06, 2008
JungleBus Systems Post: Ice Protection
I recently had a passenger stop at the flight deck during deplaning to say hi to me and the FO. It turned out that he's a Private Pilot with an instrument rating, and flies a nearly-new Cessna 172 with a Garmin G1000 glass cockpit, traffic information system, and weather datalink. We marveled at the advances in general aviation avionics the past few years, and I remarked to him that his cockpit was as sophisticated as ours for a mere fraction of the cost. "Yeah," he said wistfully, "but it's still a single-engine piston, and despite all the goodies I still can't fly it half the winter."
It's a good point. Advanced avionics have brought light aircraft up to transport category standards in many respects and greatly improved their usefulness, but icing remains a significant problem for light aircraft. Despite some advances in technology to make anti-ice equipment lighter and cheaper, only some light twins and very few singles are approved for flight into known icing. A lot of the equipment is of dubious effectiveness, and prudent pilots don't remain in icing conditions for long even in "known ice" airplanes. Transport category jets, on the other hand, have had icing pretty well licked for over 40 years. This is in large part due to their superior performance: icing conditions tend to be pretty localized both by area and altitude, so aircraft with plenty of speed and power can blow through icing too quick for it to be much of a problem. Icing at cruise altitudes is rare for jets; the air is usually too cold to support enough moisture for significant icing. Jets have a significant advantage in the equipment department, too. They enjoy a steady supply of hot air from their engines' bleed valves, which is used to heat the wings, tail, and engine inlets. It's been an effective system since its inception, and has been adapted on most jet aircraft from the DC-8 until today - although the B787 will soon be a notable exception.
The JungleBus is no exception. Its ice protection equipment is pretty standard for a jet, although the operation is more automated than most aircraft. The leading edges of the wings are heated by bleed air via the pneumatic system; the engine intakes are heated by air that comes directly from the 10th stage compressor bleed. Both vertical and horizontal stabilizers are unheated; this is noteworthy but not unprecedented. The manufacturer had to prove during certification tests that the aircraft was not prone to tailplane stall or control problems with unusually heavy ice accumulation on the tail. I know - I'm not utterly convinced, either. The remainder of the anti-ice system is electric; protected areas include both windshields, the Air Data Smart Probes (pitot/static/AOA) and True Air Temperature (TAT) probes.
A key difference between hot-wing anti-ice systems on jets and the inflatable rubber de-ice boots used on smaller aircraft is when they should be turned on. Despite some controversy on the subject, most pilots still wait to inflate their de-ice boots until there has been some accumulation of ice. Anti-ice systems, however, must be turned on at the first sign of icing (or before). You don't want ice to build up on the cowl inlet only to be ingested into the engine when the cowl is heated; it can do a lot of damage to the compressor blades. Likewise, applying heat to a wing leading edge that already has a significant accumulation of ice can cause it to melt and refreeze further aft on the unprotected portion of the wing. Because it's hard to see the wing tips on most swept-wing airplanes, you have to rely on other cues to know when you've started accumulating ice. The windshield wiper often accumulates ice before any other part and makes for a good visual first warning. Transport category aircraft are also required to be equipped with ice detectors. These ingenious devices are metal rods that protrude from the nose of the aircraft which are vibrated at a particular frequency. Any ice accumulation will change the frequency of the vibrations, triggering an icing warning in the cockpit. Occasionally the detectors are heated to knock off existing ice so they can determine whether icing conditions still exist.
On most aircraft, the various icing systems must be turned on manually. Most operators direct their pilots to do so when entering potential icing conditions (clouds or visible moisture near or below freezing temps), or at the latest when the ice detector gives an icing indication. This is where the JungleBus departs significantly from previous designs; it makes normal operation of all anti-ice systems fully automatic. The ice protection panel is a collection of dusty switches that rarely get touched; so long as the mode selector remains in AUTO, the system will automatically turn on wing and engine anti-ice whenever the ice detectors sense icing conditions from shortly after takeoff until landing. Meanwhile the windshields are protected any time there are at least two sources of AC electrical power, and the probes are heated automatically whenever an engine is running or manually via a button on the FO's main panel.
There is some manual control of the system for abnormal operations and for takeoff. Although the mode selector is normally left on AUTO, turning it to ON manually activates engine and wing anti-ice (on engine start and liftoff, respectively). Individual selector buttons for the wings, each engine, and each windshield allow each component to be manually deactivated. These are seldom used except when components fail. Manual control of anti-ice systems for takeoff via the Flight Management System is much more common. Using bleed air robs the engine of compressed air for combustion and therefore use of wing and engine anti-ice results in decreased power output. For this reason, the JungleBus inhibits automatic operation of both wing and engine anti-ice until reaching 1700 feet AGL after takeoff. If anti-ice protection is desired for takeoff, the pilots must set it on the Takeoff Dataset Page of the Multi-Function Control Display Unit (MCDU, otherwise known as the FMS head). The standard mode, which inhibits anti-ice until 1700 feet AGL, is OFF. Turning it to ENG mode turns on engine anti-ice as soon as the engine is started. The ALL mode enables engine anti-ice on engine start and wing anti-ice when wheel speed exceeds 40 knots on takeoff. In both cases, the anti-ice systems revert to automatic operation once the plane reaches 1700 feet AGL.
At NewCo we turn the dataset to ENG mode if there is any precipitation falling or any surface contamination with a static air temperature of less than 10 degrees C, and we use ALL mode if there is visible moisture below 1700' AGL with a SAT of less than 5 degrees C. Of course we won't get any wing protection until achieving 40 knots on takeoff, so any prior contamination must be removed with de-ice fluid (Type I). This provides limited protection for active icing conditions on the ground (ie falling snow) so in many cases we follow application of de-ice fluid with a second coat of anti-ice fluid (Type IV). This is designed to absorb the falling precipitation and then shear off the wing during the takeoff roll, at which point the aircraft's own anti-ice systems will be protecting it.
Like most aircraft systems on the JungleBus, there is a dedicated synoptic page for the anti-ice system on the Multi Function Display (MFD). It displays the status of the bleed and anti-ice valves, pneumatic system pressures, and bleed air & wing duct temperatures. A color-coded schematic of the system makes it easier to quickly understand any abnormal conditions.
One annoyance of the JungleBus' ice protection system is that the ice detectors interact with the Stall Protection System with no provision for pilot intervention. Once ice is detected, the SPS will assume it remains on the airframe for the remainder of the flight and increase stick shaker & pusher speeds accordingly. This forces the pilots to use faster approach and landing speeds, which would be the correct thing to do anyways if the aircraft was actually loaded up with ice. It is, however, pretty ridiculous to be forced into using ice speeds to land in Dallas on a 90 degree day just because you picked up a trace of ice on climbout from Minneapolis several hours ago.
All in all, though, the JungleBus' ice protection system works pretty well. Last winter I had a few occasions where the ice built up pretty good on the windshield wiper before landing, and post-flight inspection revealed significant accumulation on unprotected surfaces but the heated portions of the wings and cowls remained absolutely clean. The aircraft handled quite well despite having a decent amount of ice on the nose, wing roots, and (gulp) tail. Really, the JungleBus' best ice-fighting technology is its thrust-to-weight ratio. Although transport category aircraft do have better equipment for dealing with ice than light aircraft, prudent airline pilots use it the same way as prudent private pilots: to keep ice accretion to minimum while exiting icing conditions ASAP. Being able to climb rapidly through icing layers means that the JungleBus' good ice protection comes in handy primarily when you find yourself stuck at a bad icing altitude for several minutes on approach.
We're supposed to get snow tonight so I think it won't be long before I put this knowledge to practical use. In my next post, I'll delve more deeply into de-icing ground procedures.
It's a good point. Advanced avionics have brought light aircraft up to transport category standards in many respects and greatly improved their usefulness, but icing remains a significant problem for light aircraft. Despite some advances in technology to make anti-ice equipment lighter and cheaper, only some light twins and very few singles are approved for flight into known icing. A lot of the equipment is of dubious effectiveness, and prudent pilots don't remain in icing conditions for long even in "known ice" airplanes. Transport category jets, on the other hand, have had icing pretty well licked for over 40 years. This is in large part due to their superior performance: icing conditions tend to be pretty localized both by area and altitude, so aircraft with plenty of speed and power can blow through icing too quick for it to be much of a problem. Icing at cruise altitudes is rare for jets; the air is usually too cold to support enough moisture for significant icing. Jets have a significant advantage in the equipment department, too. They enjoy a steady supply of hot air from their engines' bleed valves, which is used to heat the wings, tail, and engine inlets. It's been an effective system since its inception, and has been adapted on most jet aircraft from the DC-8 until today - although the B787 will soon be a notable exception.
The JungleBus is no exception. Its ice protection equipment is pretty standard for a jet, although the operation is more automated than most aircraft. The leading edges of the wings are heated by bleed air via the pneumatic system; the engine intakes are heated by air that comes directly from the 10th stage compressor bleed. Both vertical and horizontal stabilizers are unheated; this is noteworthy but not unprecedented. The manufacturer had to prove during certification tests that the aircraft was not prone to tailplane stall or control problems with unusually heavy ice accumulation on the tail. I know - I'm not utterly convinced, either. The remainder of the anti-ice system is electric; protected areas include both windshields, the Air Data Smart Probes (pitot/static/AOA) and True Air Temperature (TAT) probes.
A key difference between hot-wing anti-ice systems on jets and the inflatable rubber de-ice boots used on smaller aircraft is when they should be turned on. Despite some controversy on the subject, most pilots still wait to inflate their de-ice boots until there has been some accumulation of ice. Anti-ice systems, however, must be turned on at the first sign of icing (or before). You don't want ice to build up on the cowl inlet only to be ingested into the engine when the cowl is heated; it can do a lot of damage to the compressor blades. Likewise, applying heat to a wing leading edge that already has a significant accumulation of ice can cause it to melt and refreeze further aft on the unprotected portion of the wing. Because it's hard to see the wing tips on most swept-wing airplanes, you have to rely on other cues to know when you've started accumulating ice. The windshield wiper often accumulates ice before any other part and makes for a good visual first warning. Transport category aircraft are also required to be equipped with ice detectors. These ingenious devices are metal rods that protrude from the nose of the aircraft which are vibrated at a particular frequency. Any ice accumulation will change the frequency of the vibrations, triggering an icing warning in the cockpit. Occasionally the detectors are heated to knock off existing ice so they can determine whether icing conditions still exist.
On most aircraft, the various icing systems must be turned on manually. Most operators direct their pilots to do so when entering potential icing conditions (clouds or visible moisture near or below freezing temps), or at the latest when the ice detector gives an icing indication. This is where the JungleBus departs significantly from previous designs; it makes normal operation of all anti-ice systems fully automatic. The ice protection panel is a collection of dusty switches that rarely get touched; so long as the mode selector remains in AUTO, the system will automatically turn on wing and engine anti-ice whenever the ice detectors sense icing conditions from shortly after takeoff until landing. Meanwhile the windshields are protected any time there are at least two sources of AC electrical power, and the probes are heated automatically whenever an engine is running or manually via a button on the FO's main panel.
There is some manual control of the system for abnormal operations and for takeoff. Although the mode selector is normally left on AUTO, turning it to ON manually activates engine and wing anti-ice (on engine start and liftoff, respectively). Individual selector buttons for the wings, each engine, and each windshield allow each component to be manually deactivated. These are seldom used except when components fail. Manual control of anti-ice systems for takeoff via the Flight Management System is much more common. Using bleed air robs the engine of compressed air for combustion and therefore use of wing and engine anti-ice results in decreased power output. For this reason, the JungleBus inhibits automatic operation of both wing and engine anti-ice until reaching 1700 feet AGL after takeoff. If anti-ice protection is desired for takeoff, the pilots must set it on the Takeoff Dataset Page of the Multi-Function Control Display Unit (MCDU, otherwise known as the FMS head). The standard mode, which inhibits anti-ice until 1700 feet AGL, is OFF. Turning it to ENG mode turns on engine anti-ice as soon as the engine is started. The ALL mode enables engine anti-ice on engine start and wing anti-ice when wheel speed exceeds 40 knots on takeoff. In both cases, the anti-ice systems revert to automatic operation once the plane reaches 1700 feet AGL.
At NewCo we turn the dataset to ENG mode if there is any precipitation falling or any surface contamination with a static air temperature of less than 10 degrees C, and we use ALL mode if there is visible moisture below 1700' AGL with a SAT of less than 5 degrees C. Of course we won't get any wing protection until achieving 40 knots on takeoff, so any prior contamination must be removed with de-ice fluid (Type I). This provides limited protection for active icing conditions on the ground (ie falling snow) so in many cases we follow application of de-ice fluid with a second coat of anti-ice fluid (Type IV). This is designed to absorb the falling precipitation and then shear off the wing during the takeoff roll, at which point the aircraft's own anti-ice systems will be protecting it.
Like most aircraft systems on the JungleBus, there is a dedicated synoptic page for the anti-ice system on the Multi Function Display (MFD). It displays the status of the bleed and anti-ice valves, pneumatic system pressures, and bleed air & wing duct temperatures. A color-coded schematic of the system makes it easier to quickly understand any abnormal conditions.
One annoyance of the JungleBus' ice protection system is that the ice detectors interact with the Stall Protection System with no provision for pilot intervention. Once ice is detected, the SPS will assume it remains on the airframe for the remainder of the flight and increase stick shaker & pusher speeds accordingly. This forces the pilots to use faster approach and landing speeds, which would be the correct thing to do anyways if the aircraft was actually loaded up with ice. It is, however, pretty ridiculous to be forced into using ice speeds to land in Dallas on a 90 degree day just because you picked up a trace of ice on climbout from Minneapolis several hours ago.
All in all, though, the JungleBus' ice protection system works pretty well. Last winter I had a few occasions where the ice built up pretty good on the windshield wiper before landing, and post-flight inspection revealed significant accumulation on unprotected surfaces but the heated portions of the wings and cowls remained absolutely clean. The aircraft handled quite well despite having a decent amount of ice on the nose, wing roots, and (gulp) tail. Really, the JungleBus' best ice-fighting technology is its thrust-to-weight ratio. Although transport category aircraft do have better equipment for dealing with ice than light aircraft, prudent airline pilots use it the same way as prudent private pilots: to keep ice accretion to minimum while exiting icing conditions ASAP. Being able to climb rapidly through icing layers means that the JungleBus' good ice protection comes in handy primarily when you find yourself stuck at a bad icing altitude for several minutes on approach.
We're supposed to get snow tonight so I think it won't be long before I put this knowledge to practical use. In my next post, I'll delve more deeply into de-icing ground procedures.
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