Showing posts with label flying. Show all posts
Showing posts with label flying. Show all posts

Tuesday, March 12, 2019

Caravan Flights Into Icing

Caravan Flights Into Icing
by Mari Peterson

As pilots we are trained to exit icing conditions when they present themselves, and as pilots we know that icing conditions are ever-changing. Sometimes the conditions can be exactly right for ice, and you get nothing. Sometimes the opposite. 

The de-ice boots on the Caravan provide some protection for removing ice, but just because an aircraft is approved for flight into icing conditions doesn't mean that you should remain in that environment and continue to accumulate more.



Ice alters the airfoil surface, making us test pilots for a new type of wing shape - therefore the boots are really a tool for exiting an icing situation. The nice part about the Northwest is that the conditions usually change within a few minutes and the situation resolves itself and the short hops between Seattle and the islands sure help too.

Be sure to treat every icing scenario as it's own independent event and to know your indicators and actions: loss of airspeed, autopilot checks etc. Most importantly, have fun and fly safe out there!


This article was written by Mari Peterson. Follow her on Instagram! instagram.com/justplanemari

If you would like to submit an article please email us info@CaravanNation.com

Thursday, May 21, 2015

Glorious Springtime by Bob Tilden

Stories from a Night Express Caravan Cargo Pilot

Glorious Springtime
by Bob Tilden


Just as I have done for the last ten years, I have been pushing the calendar since January, trying to move winter out of the way. I have pushed the hands of the clock forward each afternoon and held them back each morning, and gradually seen the day lengths creep longer and longer as the weather has warmed. It is June now, and if only I could stop the calendar I would be delighted.

Our late spring daylight lasts almost 16 hours, a span that was unimaginable just six months ago. Winter's air can smell crisp and fresh at best, and a winter evening can be splendid in its silence, but today the air is alive. The scents of a billion blossoms waft through the air, and our songbirds have returned to fill it with their songs. Life is good; I no longer find myself scanning the lead- gray winter sky at sunset, wondering of the stealthy ice- demon will visit upon my airplane as it flies through the gloomy night.

Airframe icing is predictable in that any flight through clouds at typical winter temperatures will cause ice to form on the plane. Some clouds are almost dry, some are quite juicy, and often there is an altitude that will be above, below, or in between the cloud layers. A thousand feet or a few miles can be the difference between severe ice and a "free pass", but you never know what awaits you. Whether to climb, descend, or change course is usually no more than an informed guess, which is why it is called "fishing". Ice, especially at night when clouds cannot be seen, is stealthy.

Thunderstorms, especially at night, are not stealthy. You can see where they are and where they aren't, and the airplane's radar can usually pick out trouble spots farther ahead Sometimes the storms sweep along in lines, usually driven by a cold front, or sometimes they will be triggered by localized heating of warm humid air and float along as cells, clusters, or short lines. Last week we had examples of all these different storms.
Much to my delight, I missed all of them, partially out of luck, but mostly because the locally generated storms start to die off as the sun drops towards the horizon. Without the sun's heat, the temperatures of the earth start to even out, and the strong updrafts that seed these storms diminish. Additionally, thunderstorms which are caused by colliding air masses, such as fronts, are always weaker and less volatile when the heat of the sun is not a factor.

Volatility, or the propensity for thunderstorms to form abruptly, is the scariest part of thunderstorm flying. Last Friday I watched the Weather Channel radar as the entire Tug Hill Plateau area lit up with thunderstorms well ahead of a line that was still well to the west. The whole area went from zero to red in twenty minutes; a pilot leaving Syracuse for the north country could have been very rudely surprised. One morning last year I watched the airplane's radar as my clear path around a cluster rapidly become a box canyon as storms developed on the outside flank and far ahead as well. There was no gracious way to avoid the weather, and I had to parallel the path upwind of the storms for quite a ways before I could get past safely.

The airplane's radar is more than a tool, it is a machine; its operation and interpretation must be learned and practiced. Sometimes it exaggerates the extent of the problem, sometimes it understates the problem, and sometimes it can actually lead you into the worst part of a storm. In any case, it only shows a narrow pie slice of the sky directly ahead of the plane, and once the rain really starts, our smaller radar units become useless. Properly used, it helps the pilot guess.

My choice between summer weather and winter weather? No doubt it is the same as yours. Thunderstorms might inconvenience us for a few hours or maybe not at all. Winter weather is a full time problem, from frozen plumbing, to balky cars, stinging wind, slippery roads, bottomless mud... and old bones that are no longer invigorated by the challenge.

Last week I was leisurely spreading a pile of driveway gravel. The still air was hazy, hot, and humid... but as I am now inclined to say, "at least it wasn't snowing". The air was filled with the fragrances of several flowering bushes, and the Oriole's song floated over the sparse midday conversations of the woodland birds. I thought of the last few weeks, getting on hands and knees to smell the first dandelions and daffodils, and later embracing the apple trees and lilacs. I delighted in the first robin's song, and waited patiently to hear the first arrivals of tohees, catbirds, and wood thrushes.

Time has marched its grand circle and brought us back to this wonderful place, but unfortunately it will continue its trek. For now though, like an old gray woodchuck, I am happy to look around, feel the sun, smell the breezes and say "I've made it through another winter!"



This picture doesn't really relate to the glory of springtime, but it shows what I was looking at as I skirted the storms that I mentioned. The picture is of the radio stack which is located in the center of the airplane's instrument panel. The left stack, from top down is the audio switching panel, the number 1 comm/ nav radio, the number 2 comm/ nav, and the radar display. The right stack is the GPS receiver, the ADF, the number 1 transponder, and the number 2 transponder.

The GPS is set to the pictoral display mode, where the current direction of flight is "straight up". There is a line that leans on a diagonal to the left; that is the straight line course from COATE intersection in northern New Jersey to the Lake Henry VOR northeast of Wilkes- Barre PA, my normal course. I have already turned about 10 degrees left of that course to avoid the storms

Looking at the radar display, the left- most thunderstorm cell (the red area) is right about where the diagonal line... my original course... would have taken me. I have already turned left to avoid it, but the yellow areas have erupted ahead of me on the new heading. Soon after this picture, I turned further left and watched the yellow areas fill with red centers. I flew west for thirty miles before turning north to regain my original northwest course.


The author Bob Tilden flew a Caravan for a Night Express cargo company for 10 years and has also written a book, Gone Flyin', to order it, visit goneflyin.com or search Gone Flyin' on ebay.com

- CaravanPilot.com

Sunday, April 12, 2015

Too Cold for Ice by Bob Tilden

A Night Express Caravan being de-iced with heated propylene glycol.

Too Cold for Ice 
by Bob Tilden


"I would enjoy this kind of weather from now until April" was a common expression during the last two winters. We had many mild spells, and few snow storms. Expressing a sentiment towards the sort of winter that meets your own personal preferences is probably a selfish thought, but since we have no control over the weather, its probably forgivable too. Us normal folks should respect the fact that some people spend their summers hoping for a cold and snowy winter.

The last few weeks seem to show a trend for a cold winter in the northeast, and it suits me just fine. In fact, I'd enjoy this kind of weather until April. If the temperature is going to be cold, I'd prefer it to be very cold, because colder temperatures mean less trouble with icing.

Icing, the accumulation of ice on the airplane during flight, is a bigger problem than thunderstorms are. Thunderstorms are not as frequent in summer as icing is in winter, and thunderstorms are loud and boisterous, not stealthy like icing is. It is never a mystery where thunderstorms are, but icing problems can exist in a wide range of winter clouds. Most winter flight planning must consider altitude and routing which minimizes exposure to icing conditions.

Ice will form on the forward face of every part of the airplane's exterior almost any time that it flies through a cloud that is below 32 degrees. It collects on the leading edges of the wings and tail, on the propeller blades and around the engine air intake, and on the antennas, the landing gear, the windshield, and every little doo-dad that is protrudes from the plane. It cuts the efficiency of the wings, engine, and propeller while at the same time, adding weight and aerodynamic drag. It is 100% bad news because the aircraft requires more power when it is crusted with ice, but the ice reduces the power that the engine and propeller can deliver.

The good news is that all clouds are not created equal, and the sky is seldom filled with clouds at all levels. Clouds with a strong moisture feed, such as the ocean, the great lakes, or a strong south wind ahead of a cold front that stretches to the Gulf of Mexico can be a problem. Weather arriving directly from the west such as we have had for the last few weeks is little threat because it is colder and dryer than storms which swing up from the southwest.

Ice that remained on the wing of the Caravan after climbing through a layer of lake- effect clouds.

The problem of aircraft icing lays in the fact that the water within a cloud does not automatically freeze when the temperature drops below 32 degrees. It needs a bit of a nudge. Clouds at a temperature of 30 degrees will typically be composed of tiny drops of water, which are not inclined to freeze unless something like an airplane bumps into them. At this temperature, the water in a particularly moist cloud will strike the airplane and stream backwards on the wings and tail before it finally freezes. Ice such as this will build quickly, and will overwhelm the airplane's de-icing devices.

The atmosphere's ability to hold moisture decreases with temperature. As the temperature decreases, the cloud's moisture content drops, and the water droplets begin to freeze spontaneously. As more of the cloud's moisture freezes it becomes less of a threat. Any remaining water droplets freeze on contact with the plane and remain on the very leading edge of the wings and tail, where the accumulation can be managed with the deice systems. Somewhere between 15 and 5 degrees, the clouds become so dry, and the moisture so frozen that they can almost be ignored, just as though they were above 32 degrees.

The Cessna Caravan that I fly has been called an "ice magnet" because it is simple, boxy, and utilitarian rather than sleek and fast. It has landing gear, wing struts, and a large external baggage pod which are exposed to the slipstream and provide so many "extra" places for ice to collect. Adding insult to injury, the airplane is under powered compared to the multi-engine planes that are more typical of commercial service.

The plane had a full complement of deice devices however. There is a "hot plate" over part of the windshield which maintains a small area of ice- free viewing, there are heating pads at the roots of each propeller blade, and there are inflatable deice boots on the leading edges of the wings, tail, struts, and parts of the landing gear.

The windshield and propeller anti- ice systems are electrical resistance heaters, but the rubber deice boots are pneumatic. Air is bled from the engine compressor section and sent to chambers within the boots, causing them to puff up rapidly, and break the ice that has stuck to them.

Too cold for ice? Yes, there is such a thing. Once you are aware that clouds do not freeze until 10 degrees or so, and that cooler air can hold less moisture than warmer air, the concept is not hard to understand. It is closely related to the more familiar concept that it is "too cold for much snow to fall".


The author Bob Tilden flew a Caravan for a Night Express cargo company for 10 years and has also written a book, Gone Flyin', to order it, visit goneflyin.com or search Gone Flyin' on ebay.com

- CaravanPilot.com