Identifying and Avoiding Ice

by HPA · January 19, 2013

When Winter Attacks

by Hank Gibson, CSIP, Gold Seal, CFI, CFII, MEI, AGI

Aircraft Icing

With winter on the way, all pilots know what that means. When it gets cold and cloudy, hello icing conditions. Pilots without any kind of de-icing or TKS system on their airplanes know this is a no-go. It’s always a really bad idea to go into icing conditions with no protection.

A whole new realm has opened up in the general aviation market in the last ten years with the advent of TKS and now FIKI equipped aircraft. TKS equipped airplanes are still not certified for flight into known icing. The system is to simply allow escape of inadvertent icing conditions. A FIKI, or Flight Into Known Icing, equipped aircraft is certified for flight into known icing, but it is only recommended for light or moderate icing. To summarize, having either of these systems on the airplane does not give a pilot a pass on determining the weather conditions.

Icing Formation

How do you know when conditions are conducive to icing? There are a couple of ingredients necessary for ice to form: visible moisture, supercooled liquid (which I’ll get into shortly), and a temperature range between 2 C and -20 C. It’s interesting to point out that ice can form above the freezing temperature (2 C is the warmest you’ll see ice), but ice will always melt when the temperature goes from below freezing to above freezing.

Why does this happen? Well, we have to take into consideration the temperature of the surface the ice is forming on, not just the outside air temperature (OAT). Let’s say the OAT at 6,000 feet is 1 C. If the airfoil were stationary at 6,000 feet, it’s temperature would also be 1 C.

Completely Iced Wing

Obviously, this is not the case with an airplane. It is always moving through the air. This is where aerodynamic cooling comes in to play. To the wing of a Cessna Corvalis moving through the sky at 180 knots True Airspeed (TAS), aerodynamic cooling lowers the temperature of the airfoil to the freezing point or lower. Therefore, when the airfoil that is below freezing comes into contact with moisture that has a temperature above freezing, the airfoil lowers the temperature of the moisture causing it to freeze.

An analogy to help with understanding can be applied here. Compare the airfoil moving through the air to the wind chill we feel on the ground in the depths of winter. The air temperature could be 40 F, but with the wind chill it could feel like 25 F (that would have to be a pretty strong wind, but it is possible in the northern parts of the US and Canada). The air temperature wouldn’t be freezing, but with the wind, it would certainly feel like it was below freezing.

Back to the point about ice always dissipating at the melting point. Whenever the temperature goes from below freezing to above freezing, no matter what the surface is the ice is stuck to, it’ll melt. This is a more hard and fast rule, termed the melting point. If you are ever in icing conditions, find some air that is at the melting point or higher and the ice will melt.

Types of Icing

There are four different types of icing conditions: rime, clear, mixed, and super-cooled liquid droplets (SLD). Clear ice is clear, as it’s name implies. It usually forms at the warmer temperatures, 2 C to -10 C. Rime ice has a milky, opaque look to it. It will form between -10 C and -20 C. A combination of the two, called mixed ice, is when the conditions aren’t favoring one or the other.

A very dangerous situation can happen when a pilot gets into supercooled large droplets (SLD). Because of their size, these droplets retain a liquid form even though the temperature of the droplet is below freezing. When an SLD strikes the surface of the aircraft, it begins to freeze on impact. The other problem is the parts of the droplet that didn’t strike the aircraft initially roll back along the wing and freeze behind de-ice equipment.

How will you know if you run into SLD? An easy sign to watch for is splattering rain on the wind screen. If it goes on for a while unnoticed, you could start to see unusual trim settings, added power needed for certain attitudes, and non-responsive controls. When any of this is noticed, turn around immediately, climb or descend 2,000-3,000 feet, and stay clear of all known icing conditions.

In the winter months, ice is always a possibility on cloudy days. Regardless of your equipment, always make a PIREP to ATC letting them know about your icing encounter. If you have a quick, heavy buildup of ice, get out immediately. Don’t take off with any kind of ice or frost on your wings. Fly safe so you can see Christmas next year.

Snow Covered C-17

How it Started

One of my best friends in high school, (Doug Gray) was a private pilot. He offered to take me up for a flight in a 1967 Cessna 150, N6228S. We took off from Calhoun, Georgia, and he took me on a scenic tour of the area, I was hooked. I later found out that my English teacher, (Jan Haluska) was also a flight instructor and the school was offering a ground school course the next year, which he taught, along with flight training with the goal of becoming a private pilot. I managed to talk my dad into funding the training, at the time the total cost was right around $500. Cessna 150 rental rates where $12 an hour, and the 172 we used for cross country was $15 an hour including fuel.

Training Begins

It started August of 1977. The fall semester rolls around, and I am enrolled in ground school, and if memory serves me, we met twice a week. First came the paperwork for my student pilot certificate, which at the time was included with the 3rd class medical. I loved ground school, especially learning navigation, plotting courses on the sectional, again this was before iPads and GPS, so we did a lot of dead reckoning and VOR navigation for cross countries. At the end of the course, I made an 83% on the Private Pilot written exam, remember this was before we had the question-and-answer books that on future test I would consume before taking a written.

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Flying

The fun really began on August 22, 1977, it was my first flight. To my surprise we used the same Cessna 150, N6228S that my friend Doug Gray had taken me for a ride in. The Cessna 150 had a standard VFR instrument panel, with one NAV/COM, and one VOR CDI. No intercom, so no headset, at the time I didn’t know what I was missing. I didn’t get my first headset until I started my instrument training in 2003. I was a big guy, I was 6’ 4” and weighed 245 lbs. but I do not remember being uncomfortable in the 150 even with the instructor in the right seat.

First flight lasted .8 hours, and we accomplished orentation, shallow turns, stability, and effects of flight controls. Over the next few months we added steep 720’s, slow flight, stalls, turns around a point, S-turns, emergencies, landings, (short field, soft field and normal).

Learning

At this point I want to talk about a training experience that still stands out. We were close to solo and were practicing takeoffs and landings. Turning base to final Jan got very upset at the way I was cross controlling the aircraft. Cross control is when you are in, say a left turn, and use opposite rudder to line the nose up with the runway. So, he had me depart the pattern and head east to the practice area, and climbing up to 5500 feet MSL, he had me slow down to just above stalling speed, start a left shallow turn and add right rudder. As the airplane stalled I had the strangest sensation, no roller coaster has ever come close, instead of blue sky in the windscreen I was looking at brown ground, and as far as I could tell we were upside down, through the terror of the moment Jan talked me out of the spin, controls neutral, oposite rudder, pull slowly out of the dive. As we leveled off he asked me what altitude we were at, as I remember it was around 2,800 feet MSL. Then he asked me what would happen if I experenced this on base to final in the traffic pattern. The answer was obvious, I would be a pile of wreckage off the end of the runway with a very short-lived aviation career. Needless to say this cured my cross-control tendencies.

Another training event the sticks out in my mind was the first time we did takeoffs and landings at the High School runway. The runway was 1,500 feet long, not sure of the width, but it seems like we had about 5 feet on each side of the wheels when on the center line of the runway. Landing from the south you also had to go between a cutout in the trees to be able to stop in time on the runway. After getting confortable landing here every runway since seemed huge. I remember landing at Chattanooga (KCHA) on a night cross country and commenting to Jan, that I felt like I could of landed sideways on the runway, it felt that large.

Very soon after this I started wearing old shirts to all my flight lessons, the reason for this occurred on February 8, 1978. The lesson that day was stalls, takeoffs and Landing. As we were taxing back in Jan told me it was time for my first solo. I was very excited, and after some last minute advice from Jan, including watch for floating on landing the plane will be light with him not in the right seat, complete 3 takeoffs and landings to a full stop. It was a blast, and at the end of my shirt was shorter in the back because Jan cut the tail out of it signed and dated my solo [an aviation tradition]. Total flight time accumulated on the day of my solo was 18.1 hours. I was now officially a pilot with solo priveleges.

In my next article I start cross country training, when Jan decided that it would be best accomplished this in the 172. Checking out in N5970R was like moving into a 747, this started a love affair with one of my faviriote planes to date. Since this time I have flown over 900 hours in many different models of the 172 and feel like I am stepping into an old friend every time.

More about Randy here: https://www.flyhpa.com/team/randy-delong/

 

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