Icing question


Certain things just are not covered in books especially when it comes to flight planning.

I am hoping on Saturday to go up to KOWB and return on Sunday. The huge difference between last week and this upcoming weekend will be the temperatures if the forecast trues out.

Obviously you can’t (according to the books) accreate ice unless you are in visible moisture laden conditions (AKA clouds). The problem with my flight GPS direct due to MOA considerations the highest I can go is 7000 going up and 6000 coming back which this time of the year usually puts me in the action of clouds. Getting above the action may not be possible for airspace considerations unless I cancel IFR (not an option in my planning process). Going down to 4000 (or even 3000) puts me below radar coverage for parts of my flight. My experiences with clouds this time of the year usually find the clouds about 2 to 3 thousand feet thick right at my planned altitudes.

My only experience with icing is trace rime and I was in and out of the “wisps” of a stratiform cloud deck (on top) and I was surprised how **little **visible moisture it took to create the trace rime. Simple fix was to ask ATC 500 feet higher which was promptly approved.

The question is what if it’s partly cloudy? What are other peoples experience if the temperature is below freezing and there are pretty significant breaks in the clouds. Obviously one shoe doesn’t fit all, but is there a reasonable cloud cover percentage that would make it a no go vs a go decision. 50 percent cloud coverage or higher, would that be a no go for anybody? Common sense to see if there is only 20 percent coverage, it’s a go, but not so clear when you have more coverage then scattered.

I realize can check PIREPS naturally if there are any just before launch, but I also assume (we all know what that means) that it would be prudent to assume that partly cloudy conditions could cause ice build up. I also realize in the clear, that if I did get any type of ice, the clearing areas may allow for sublimination. Anybody have any experiences with freezing temps and partly cloudy conditions? Would love to hear the decision making process for those that have flown in these type of meteorlogical conditions.


If your in the clouds and it’s below freezing you might get ice… you might not. It’s that simple. Sometimes you’ll go an hour without building ice then all the sudden it starts, nothing has changed.

Know your MEA’s and the temp at the MEA’s along the route. If I can’t descend out of the ice I’m not going, not IMC anyways.

Descending into warmer air will usually stop the build but the ice you have stays for an hour or more. That always surprises me.

Snow is a good thing because it’s gathering the ice crystals and you’re not. When the snow stops there is a high percentage you’ll start picking up ice.

How does your plane handle ice? If I was in a Cirrus or SE Cessna and starting building ice I’d be much more concerned than if I was in my Super Viking. Some models build ice faster than others. Some wings fall apart faster than others.

Okay, so the bottoms drops out and you’re icing up. Don’t panic, it’s not the end of the world. Ice should be respected but too big of a deal is made of it. The plane is still flying and usually a climb or descent will get you into the clear. If you loose more than 10 knots IAS you have an issue. Find a place to land. Think twice about lowering your flaps when iced up because the wing may stall sooner than expected.

I was enroute from the LA basin to Phoenix early one morning. On the same route and altitude behind me was a Cessna 182 and 206. I started picking up very light clear ice passing Palm Springs. Never said anything, never asked for a altitude change even. I’d been seeing a slow build for 50 miles when the 182 behind started build ice. The guy went into full panic mode taking all the controllers time because the pilot didn’t have a plan. Didn’t know the temps below. Didn’t know the MEA. You could hear the heavy breathing when he spoke. This went on for 5 minutes with ATC suggesting a lower altitude, not the pilot.

No sooner than the 182 calmed down then the 206 stared building ice and it started all over again. I was embarrassed for the pilots and at the same time found it funny.

Finally Center tells them a Super Viking is same route and altitude 50 miles ahead. “01B say in flight conditions?” “IMC, smooth air, trace ice last 75 miles.” After that I was their lifeline. "How’s that Super Viking doing up there?


Thanks Frank for this kind of insight but what I am looking for is the planning stages. What makes a go / no go situation beyond knowing MEA or in my case OROCA / MORA and freezing levels.

I am looking for the decision making process that maybe the books won’t or don’t cover such as partly cloudy conditions. Like I said earlier, PIREPS are most helpful but sans that, what gives you the go ahead for wheels up?

Like you said for yourself, if it’s solid overcast and below freezing, my wheels just won’t go up as I am going to assume the icing potential is there, but if it’s partly cloudy, the waters are not so clear. If it’s partly cloudy and I can see the sun through the clouds, I will go up. Figuring the thin clouds would allow me to get safely above or below the cloud deck between 5000 and 7000. (below 5000 puts me below radar coverage in parts of my route).

Can I accreate ice under these partly cloudy conditions? (lets say 50 to 70 percent non convective cloud or fair weather cumulus coverage). Have you encountered this in your neck of the woods? My mind says yes icing is possible, but looking for those including you :slight_smile: that may have flown under partly cloudy skies and any icing encounters.

I know there is no rubber stamp yes or no decision making process but real time experience far more useful then the textbook.

For my forecasts, I have
forecast.weather.gov/MapClick.ph … 0.0038&e=0 for where I am. Friday night sets some alarm bells off for an early morning departure since temps will be near or below freezing at the surface even this far south. Clouds tend to burn off late morning.

forecast.weather.gov/MapClick.ph … 7.1193&e=0 (kinda a no brainer “go decision” as of this moment)

As you can see terrain consideration nothing like you have your way as it’s a flat area of the country.

Of course, I could do the old fashion airways and fly much lower (giving me much more padding in altitude decision) but that adds about 40 minutes flight time in which for such a short turn time, not going to be an option.


I can’t believe it! An intelligent, complimentary conversation between Allen and Frank! Could this be the olive branch we’ve all been waiting for? Stay tuned to find out!


Good move Wiser!! You just screwed it up by pointing it out! :laughing:


Now would be a great time to check to see if your pitot heat is actually working (does anyone ever check that?) and see what effect alternate static source has on your instrument readings (if equipped).


you should check it every flight.


I will have to admit, during VFR flights I do not check the pitot heat. Kinda the same for nav lights as well during daylight or VFR conditions, I don’t check them either. Of course night flights or IFR conditions I check nav lights during preflight.

When I expect to be in IMC, I check the pitot heat on preflight. I learned it helps keep that drain hole clear of water in rain. Degraded ASI while in IMC during an IA lesson and CFI got me on to putting on pitot heat to clear the issue. So, now everytime I am in rain and IMC, I put the pitot on out of habit.

No alternate static source in my plane. Not sure why, but total WAG would be I have two static ports (one on each side of the fuselage)


So allen what’d be a way to get Alt static if both get clogged?


Since I don’t have an alternate source, I think break the glass on the altimeter would be my guess to get my altimeter to read or unfreeze?

Good refresher course for me needless to say since I don’t know the exact answer. 8)


Hammer time :slight_smile:


No VSI you need your ALT


So would I be correct in implementing msh168 corrective tool and smash that glass out of the altimeter?

I personally wouldn’t even need the VSI if I have the altimeter back in service to give me reference of climbs and descents.

As I understand it, the ASI would be very unreliable for climbs and descents making it quite hazardous for approach to landings.


Life comes at you fast!


Smash the VSI, they all draw the same static source. If you smash the VSI, the Altimeter will use the static source you created by breaking the seal on the VSI. In other words, sacrifice your VSI for your altimeter.


Good clarification, msh168. With that, what flyboy said now makes sense. :smiley:


Neat trick.

Aeroperu 603 was a 757 that went down because all of the static ports were taped-over for cleaning. Anything like that that they could’a done? Or would cabin pressure be a factor. Looks like the 757’s VSI is “glass”, so maybe the trick wouldn’t work on it because of that…


Make that a ditto here as well!

I know my knowledge of systems is weak so refreshers of this nature always nice. 8)


The IVSI probably has a transducer, so that wouldn’t have helped. We have the same IVSI in our TCAS II airplanes, and the static line does come into the airplane and into the IVSI, but there is a transducer in the instrument. You’d still have to dump the cabin and look at the cabin altimeter.

Our guys have devised a clever static port cover with Caution tape and a “NO TOW” flag on the nosewheel for whenever they have to cover the static ports. That’s probably the only type of thing that could have saved them unfortunately.

EDIT: Without reading all the particulars again, if they did as I described above, they might have been able to see the altitude on the cabin altimeter up to ~about 14000’. I’m not sure how the pressurization is displayed on the 75 though.


Gotta luv flight planning…

This mornings forecast (which I am sure will flip flop 15 times before Saturday) has a 30 percent chance of snow Friday night and Saturday morning along my route of flight (north central and north MS)…

I thought I lived in the deep south???