It’s All About the Ice

It’s All About the Ice

It’s All About the Ice

Ice is a difficult hazard to predict. But in the Pacific Northwest with its high MEAs, frequent IFR conditions, cloud tops that rise well into the flight levels, and generally strong westerly winds aloft complicate the how to handle the ice problem.

For some reason, you long ago quit making saliva. Your mouth is so dry it is hard to swallow. Your hands are cold, but at the same time strangely wet with sweat, as are your ears under the Bose headsets. And finally, if all these symptoms of stress were not enough, you just realized a very urgent need to urinate.

The C414 you are flying is at FL180 eastbound over the mid cascades and no longer climbing even under full power. You can see little outside because even the side windows are partially iced over. The four passengers in the back are sipping coffee from a green Aladdin thermos, chatting about their construction project and seemingly not in the least worried about anything. You start to wonder if you should have ever got involved with this professional pilot thing to start with and desperately want to be on the ground.

In the Pacific Northwest during the winter months, this experience happens all too often to pilots who have just started flying professionally, or pilots in their own aircraft and not familiar the area. Ice is probably the most difficult hazard to predict. But high MEAs, frequent IFR conditions, cloud tops that rise well into the flight levels, and generally strong westerly winds aloft complicate the how to handle the ice problem. Over the years I have flown a variety of different aircraft in this setting. Without question those that have caused the driest mouth experiences and the most careful decision-making are pressurized piston twins.

Now, that may seem kind of odd given those aircraft bring benefits to the table that non-pressurized, and not turbocharged aircraft are lacking. But that is precisely the problem. The pressurized piston twins are just “good enough” to get you in real trouble. Trouble you would readily recognize and not go anywhere near in less capable aircraft (say a C182 or C310), and those that a CJ or Lear would just blast right through on the way to FL410 without any problem at all.

Using a stressful flight from Seattle (BFI) to Boise (BOI) from the distant past as an example, what follows are some of the thought processes and techniques I have learned from others (and also regrettably from bad personal experiences), in 10,000 hours of this kind of flying. Given I am still here to write the story, they must work pretty well.

It was mid-December and over the past several days there had been the typical winter low pressure system moving into the Washington State from the Gulf of Alaska. The weather at BFI was 1,400 overcast, visibility 3 in light rain. Temperature on the surface was 43 degrees F, and wind was 110 at 12. BOI reported a 1,500 overcast, visibility variable from 1 to 4 miles with occasional blowing light snow and a 28 degrees F surface temp. En route weather showed tops in the Seattle area at 17,000. Over the Cascades they are at FL210, and at BOI 10,000 feet. Winds aloft were from the west at 30 knots at 10,000 feet, and 50 knots at FL180. And as usual, light to moderate rime icing in clouds was forecast for the entire route, and pilot reports were confirming the forecast.

The flight distance was 350 nm, which given a TAS of 210 knots, plus a tailwind of about 60 knots, would take just under 1.5 hours in the C414. The airplane easily carries four hours of fuel plus the passenger load. Seemed like a pretty easy trip and not knowing any better, we filed IFR BFI direct to BOI just like we do in the summer. Off we go. Some 20 minutes later, we are climbing eastbound on our direct routing to BOI with a TAS of 140 knots, and ground speed of about 200 knots. We have covered some 65 miles since takeoff, placing us well over the Cascade Mountains and be somewhere in the mid-teens on altitude.

We were right in the middle of the worst icing conditions, and the real sneaky problem we now faced is the combination of winds aloft, cloud tops of FL210, degraded aircraft performance and our position in the middle of the Cascades. The airplane will get up to FL210, but even on a good day and without any ice on the airframe, the climb rate in a pressurized piston twin will drift down to some 400 to 500 fpm once in the flight levels. With cloud bases at 1,500 feet, and the freezing level starting at about 6,000 feet, this means that as a minimum, we would be spending a good 30 minutes either accumulating ice, or with it clinging to the airframe. Seeing that is what caused our saliva production to stop.

Now, we were taught that even in a FIKI (flight into known ice) approved aircraft, the best strategy when encountering ice is to immediately do something to get out of it. The simplest option when over flat country is to just descend into warmer air, but we were over mountains, and so that was not possible. Another option was to climb above the icing layer as fast the aircraft can. The layers where ice accumulation is at its worse, are usually only 3,000 to 4,000 feet thick, but at 400 to 500 fpm that is going to take a long time. And, even with all de-ice equipment working, residual ice on the aircraft could slow the climb rate down to nearly zero, so it was quite likely we simply don’t have the ability in this pressurized, piston-powered aircraft to “out climb” the ice.

Finally, the last option we are taught way back when, is to simply turn around. But given the winds aloft, that solution can be a death trap. To get back where we came from just 20 minutes ago with our tailwind and a groundspeed of 200 knots will now take nearly 45 minutes given the 60-knot wind from the west, plus the airplanes degraded performance. There was a fatal accident in the NW some years ago, wherein the groundspeed problem alone precluded the pilot from reaching warmer air and lower terrain before his impossibly iced-up twin, still descending even at full power, crashed into a mountainside.

The only remaining option was to do exactly what we were taught NOT to do, which was fly on straight ahead, taking advantage of the tailwind to get us over the crest of the Cascades on over lower terrain as soon as possible. Looking out of the nearly iced-over side window, ice was rapidly accumulating on all parts of the airframe we can see, making proceeding on a very precarious and difficult choice to make.

You only have a neophyte experience once before you learn there are some very effective strategies that can be used to avoid this situation from ever presenting itself. 

One of the most basic procedures is to make sure the airplane is well above the icing (that is on top of the clouds), before departing the safety of sea level terrain. To implement this procedure, on the first call to departure control once off BFI request vectors “for ice avoidance” that keep the airplane over or near Puget Sound until it is on top. Upon hearing that request, the controller would probably extend the departure leg to the NW, and then clear the aircraft direct to back SEA then to the flight plan route. Most departure controllers in the Northwest understand the ice problem and are very cooperative in helping the pilot avoid it. The “ice avoidance” request, however, needs to originate with the pilot. Making such a request is the professional thing to do as it shows you are planning well ahead of the aircraft.

If ice is encountered that stops airplane from climbing while still over sea level terrain, you can always quite safely descend to nonfreezing conditions without hitting anything, and without even requesting much special handling from ATC. When flying near or over salt water on the West Coast, it is helpful to know that ocean temperatures from the Gulf of Alaska to Northern California rarely are colder than 45 degrees F. This “heat source” almost always produces ice-free air below 3,000 or 4,000 feet when over or near salt water, and the MEAs over that water are typically well within those altitudes.

The next question is given the conditions, what should your flight plan route actually be. Clearly the direct one chosen on the above flight was not wise. The lowest mountain crossing MEA is 6,500 and involves using V2 from SEA to BEEZR intersection, and from there direct to Yakima (YKM), but it is slightly out of the way. An alternative would be to use V4 from SEA to YKM, which is direct but with an MEA of 10,000 feet. From YKM, V4 goes more or less direct to BOI with MEAs on the order of 9,000 feet. When it was new and the C414 airframe was ice free, the book says it could maintain 14,000 feet on one engine. But there are lot of “ifs” in there, so the best route would be the one with the lowest MEA, which is V2, SEA, BEEZR, YKM. The direct route at least from SEA to YKM would not be advisable as the MEAs and terrain are much higher.

So even with a route plan that takes the airplane over manageable single-engine MEAs you still really want to be above the cloud tops before proceeding eastbound. But sometimes, regardless of forecast, the cloud tops exceed the altitude capability of pressurized piston-powered airplanes. If this happens while still over sea level terrain, the flight to that point would had to have been pretty much ice-free in order for me to feel comfortable continuing eastbound and away from the safety of the lower terrain and warmer temperatures below. If we had been fighting ice all the way up, and were unable to get or stay on top, even though in a de-iced and turbocharged and pressurized airplane, the best thing for an experienced, mature and professional pilot to do is call it a day and simply not go further east. When operating in the Pacific Northwest there is a rule in this regard that is helpful to remember: “With winds from the west, do not proceed eastbound until certain there will be no need to return.”

Finally, after managing to cross the Cascades and approaching BOI, we need to do some ice-related descent planning. Given the 28-degree temperature at the surface, some ice should be expected during the descent, and if that ice was bad enough, it could force the airplane all the way to the ground even with the FIKI system running full blast. For this reason, I would not want to start my descent from “on top,” until relatively close to BOI and would so notify the controller.  

Before starting the descent, I would make sure the cabin pressure rate controller was set to no more than 500 feet per minute and would plan on a good 1,000 foot per minute aircraft descent all the way to the final approach point, keeping the TAS up at high cruise and the engines warm by carrying power.

One of the reasons for the high airspeed is that air moving across the wing is warmed a bit from higher speeds. Sometimes just a 20-knot change in TAS will stop ice from forming in conditions that are otherwise identical. The lower angle of attack will also help prevent ice from forming on the bottom of the wing where you can’t see it. Another reason for the high descent rate is it means the airplane will pass through whatever icing layers exist much more quickly. Basically, if we encounter cloud tops on the way down at the forecast 8,000 feet, and the altitude at the IAF (initial approach fix) is say 4,000, we would spend no more than a total of 3 or 4 minutes in the potential ice.

Now all we have to deal with is the final approach and landing. In spite of our careful “ice avoidance” descent, it is possible that with the 28-degree temperature on the ground at BOI, whatever ice accumulated on the aircraft could still be present upon landing. Making sure windshield de-ice is working is important in these conditions. Even in a FIKI airplane with boots and hot props all working, ice tends to stick to the wing in areas you cannot see, raising the stall speed by an unknown amount. For this reason, keep the airspeed higher than normal until close to the runway. In these conditions, a pilot with a professional mindset would only flight plan into airports with long runways (BOI has 10,000 feet).

Additionally, some inquiry as to braking conditions is in order before landing. If we had departed a wet runway at BFI and then climbed into freezing conditions, it’s also possible the brakes could be frozen and will not work initially after landing. Some turbine aircraft such as King Airs have a special hot air hose to the brakes for this very reason, plus the ability to reverse either the propellers or the engine thrust, piston twins do not, so you have to be extra careful.

After landing and getting clear of the runway, our problems are not yet over. In the winter there can be piles of snow that can be a problem for low wing twin-engine aircraft with their propeller blades sweeping less than a foot above the ground. So even if we know exactly where to go, if there is any question about the best route to take the best procedure is to just ask for progressive taxi instructions.

When finally arriving at the FBO and taxiing toward that lineman with the orange wands, keep your right hand on the mixture controls. You never know if a patch of ice will magically appear under your main gear just as he waves you to a stop.

After all we have been through on this trip, scaring the line guy would be a bad way to end the day.

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