known icing conditions??

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fieldinsight
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known icing conditions??

Post by fieldinsight » Fri Dec 05, 2008 3:14 pm

Hi all,

Just a very general query to the more experienced Flyers out there;

With the cold temps etc being experienced across the country at the moment, we will say on average at or below 5C; and allowing for air temp reducing by 2C for every 1000' (ISA) foot gained on the altimeter,

obviously staying clear of the clouds etc, is it possible for a GA flight to be in known icing conditions say flying at 2000' with outside air temp at OC??

Does the likelyhood increase if cloudbase was overcast as supposed to few?

Thanking all in advance!

fieldinsight

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hum
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Known icing

Post by hum » Fri Dec 05, 2008 5:16 pm

With the exception of freezing rain or drizzle you will not get airframe icing if you are clear of cloud.

You need visible moisture (cloud, rain, drizzle) to form structural icing.

Good info here:

http://www.aopa.org/asf/publications/sa11.pdf

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Post by N714GZ » Fri Dec 05, 2008 5:36 pm

Airframe Icing conditions exist when you get BOTH of these conditions:

OAT < 10C and
Visible Moisture

Visible moisture includes cloud, fog, rain/mist/sleet/snow

If you fly in an OAT of <10C , avoid visible moistue. Simple rule.

Having experienced icing on IFR flights(de-ice boot equipped twin), my advice would be never underestimate how quickly it can appear. Remember even a Cessna 172 can be IFR equipped and can legally be flown in IMC with an instrument rating. However for most of the year in this country it's not possible,due to the temperature and visible moisture being present and it not being de-ice/anti ice equipped. Aircraft need approval to fly into known icing conditions. Thats why a single engine IR isn't the most useful rating you could get in this neck of the woods.

Know the conditions where icing can exist and avoid them.

j3cub

Post by j3cub » Fri Dec 05, 2008 6:08 pm

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driver1a
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Post by driver1a » Fri Dec 05, 2008 8:10 pm

Hum is indeed correct, J3cub but so is N.. all the numbers.
As Hum said, no moisture no icing - the aim is to fly in VMC on top, not stay stuck in the soup.


That would indeed be the aim, but what happens when you need to descend? Or climb to get up to the nice VMC on top? There's that ice laden cloud waiting for you. In winter the icing level is often very low. In fact you can safely assume that all the cloud you see in winter has ice at it's heart. But even in summer you would be amazed at how low ice can form while flying through cloud.

I imagine if you do pick the brains of all those people who have been flying IFR for the last twenty years. They will tell you the same thing. Don't fly in cloud in winter unless you are in a fully equipped aircraft and be careful for the rest of the year too.

j3cub

Post by j3cub » Fri Dec 05, 2008 8:47 pm

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N714GZ
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Post by N714GZ » Fri Dec 05, 2008 9:10 pm

j3,

While I definitely wouldn't claim to have close to Hum's experience in this area and my new mount being in the 65 ton category and not on the lighter end of the scale, I have in the not so distant past flown a number IFR sectors in both light single and light twin aircraft. I have experienced icing in actual terms(ie on the wings!) and in planning terms, ie "we are not cleard for flight into known icing conditions, so we need to avoid this area of weather" etc.

You are much more limited in where you can fly in most single engine aircraft when icing conditions prevail. This is not simply because the aircraft is single engined, but because the fact is the majority of sngle engine aircraft are not de-ice capable and thus are not cleared for flight into "known icing conditions". Having seen how quickly ice build ups can occur, I would not like to be in a situation where descent is my only means of removing it. Im talking 30 seconds from nothing to a noticable layer.
Now you are right it is sometimes possible to fly on top of the cloud layer, but this would be isolated to the warmer months where the temperature is high enough to prevent icing in the climb through the visible moisture.
As regards the cloud tops stopping at 5-6000 feet, it really depends on the day. I have also worked as a parachute drop pilot and I can tell you that really quite often you can be dodging in between the big stuff still towering above you when at FL100...in single engine aircraft by the way. I know that the OAT can be between anywhere between -20 and -10 during the winter months and around -5 to -10 during the summer months. I would not have liked to fly through visible moisture to get there!!!

Yes any instrument rating is a useful addition to your abilities as a pilot, but it is limited by the limitations of single engine aircraft.

As regards the 172 across the Atlantic, good luck to those lads!! There is a Tipperary man working as a ferry pilot these days. If you were ever into Toomevara you might have bumped into him. I know a guy who did the same with his own Cirrus and has just done it again with his latest bird-an Eclipse 500. Well for some!

j3cub

Post by j3cub » Sat Dec 06, 2008 2:33 am

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N714GZ
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Post by N714GZ » Sat Dec 06, 2008 3:56 am

Good summary.

I should also clarify my point above re the temperature, that while you would turn on the probe heats etc when the temp is less than 10C-the risk of encountering icing increases the lower the temp and actual icing will occur at or close to the freezing level-(the altitude at which the temp is 0C, which is obviously a lower altitude in the winter months.) You could happily fly along in visible moisture all day at 5C and not encounter any icing. The problem occurs when local variations in temperature occur, for example if you inadvertantly fly into an embedded CB. In IMC you cant see it coming to avoid it, so thats where good use of forecasting and planning must come into play.

As regards the Eclipse, he had only weeks to spare. Lucky guy!
Last edited by N714GZ on Sun Dec 07, 2008 2:42 am, edited 1 time in total.

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Post by shamrock/heavy » Sat Dec 06, 2008 4:58 pm

Nice debate but I am surprised to see some people are quite content to fly in "known icing conditions" in aircraft with AFM's stating "avoid known icing conditions". The decision to climb through icing conditions to find VMC on top is not one I would make myself. What your trying to do is use the excess performance to climb(which in a light single is sweet fa anyway), but all the while your increasing weight, increasing drag, reducing lift and reducing thrust(not to mention the vibration from ice on the prop) if you do in fact encounter the forecast icing conditions.

Have you thought about the various aerials on your aircraft (comms VOR/ILS)all of which are unheated and vital for the conduct of IFR flight.Although most of these light singles have a heated pitot probe, should this fail you know have the added problem of unreliable airseed which will increase the already high possibility of stall and inadvertant entry into a spin in IMC!!. Static ports are unheated with the obvious consequence.

Also flying IFR in controlled airspace doesn't really allow for the same freedom in navigation as VFR flying. For example if flying to dublin IFR and asked to descend into the icing conditions and take up the hold at DINIL for 30 mins while faster moving commercial traffic get priority.Can you happily accept that clearance without the "ohhh shit" feeling. Not a nice position to be in, if not flying a suitably equipt a/c, and its probably now your wishing you had stayed at home today.

Although not applicable to private flying JAR-OPS says something like this, a flight shall not be commenced through known icing conditions unless the aircraft is suitably equipped to cope with such conditions. Simple. Although you may not be professional you should try to operate to the hightest standard you can 100% of the time. Make good decisions and don't tempt mother nature, she's been a bitch in the past to pilots and for sure she will in the future.

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Icy thoughts

Post by hum » Sat Dec 06, 2008 5:33 pm

Good topic this.

A few thoughts struck me reading through the above:

- If you have one, keep your Pitot heater on at all times when airborne. I believe it stops moisture getting trapped in the system and also means that it is on when you need it. You will definitely forget it one day if you rely on memory to switch it on before entering icing conditions...

- I have not seen a lot written about engine intake icing, but I suspect it happens a lot more than people realise. If you see even a thin layer of ice on your wing leading edge, think about what is happening at your engine's air intake. A lot of Cessnas for example, have an air filter mounted below the prop on the front of the cowling. If this gets blocked with ice your engine is going to be starved of air, carb heat may not help (depending on the 'plumbing' arrangements) and 'alternate air' might be the only way out if an immediate descent into warm air is not possible.

- If you dont have FIKI then stay away from ice. Even if you have a suitably equipped aircraft I would say avoid ice anyway - I don't know of any GA type that is really capable of coping with continuous icing conditions.

- It there is forecast icing below your safety altitude in either the climb or descent portion of your planned flight I would seriously consider not going unless you are very confident of remaining VMC during these critical phases.

- Someone mentioned embedded CBs above - these are a no-no.... The famous Scott Crossfield died in one of these... If forecast, the only safe way to avoid these in IMC in my opinion is a Wx radar - expensive, but IMHO a 'must have' or you don't go.

Good bedtime reading here:

http://www.caa.co.uk/docs/33/ga_srg_07webSSL03.pdf

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Post by mr crow » Sat Dec 06, 2008 7:57 pm

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Last edited by mr crow on Sun Jan 10, 2010 12:38 am, edited 1 time in total.

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Post by N714GZ » Sun Dec 07, 2008 2:33 am

Good clip Crow, illustrates pretty much everything being said above, from icing on aerials, to the importance of the freezing level and the use of weather radar.
From what I can make of the first few minutes it's a Caravan, one of the biggest singles out there. It was de ice boot equipped most probably on both wing and horizontal stabilizer leading edge. It probably had heated prop and intakes and also had wx radar, yet it still got into trouble. Perfectly illustrates Hum's point about avoiding icing conditions in any GA aircraft.
Hopefully a deterent for those willing to take even a short excursion through icing conditions in aircraft not equipped for the job. It will happen so quickly you will have seconds, not minutes, to react. When suddenly that streak of water that was making it's way along your windscreen stops in it's tracks and you look out at the wings there will already be build up. It will focus the mind to say the least. Icing conditions can and do exist here most of the year.
An interesting point to note is that pressurised singles(Hum's area of expertise), such as the 210/TBM/PC-12 have the ability to climb above the problem. The further you move away from 0C, on the plus AND the minus side of things, the less chance icing will occur. So fly in the warm air, or the really cold air. Just make sure you can climb or descend through nice clear air between the two!

A couple of things spring to mind after listening to this particular clip:

-Excellent awareness of the problem by the controller.
-Terrible awareness of the problem by the pilot.
-When an aircraft becomes uncontrollable even for a few seconds, always land. Do not continue with the flight. Assume structural damage and perform a visual inspection or better still have an engineer look the plane over.
-Land anyway-she sounded like a coffee would have settled the nerves.
-Know how to use all the equipment you have on board. It's no good having Wx radar if you cant see the rain.

4GZ

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Post by shamrock/heavy » Sun Dec 07, 2008 1:35 pm

Very good clip, thanks for sharing. Maybe this "pilot" should have taken the bus to bangor or wherever she was going. Few things to mention on this firstly a MAYDAY was declared because she couldn't control the aircraft, minutes later "i THINK everything is okay now" and she was quite happy to continue to her destination after spending roughly a minute evaluating what happened.

Straight away you've got to start thinking what happened, was it windshear?? Was i due to fly through CB's according to the sig weather chart, was i in a CB according to my weather radar, where are the showers in relation to my route and to my present position??? When asked did she see the shower i think it was 10 miles ahead the reply was not yet......... check the tilt. All the onboard equiptment is only as good as the person using it. Did i have a bird strike?? visually check each wing and the tail section for structural damage. Did i encounter icing?? what was the forecast temp at my cruise altitude, and was i flying in visible moisture?? (given a report of 0C at 4000ft) at 8500ft your right in the shit, also with the reported showers indicating the presence of CU the possibility of supercooled water droplets giving severe icing in the form on CLEAR ice, the heaviest and most dangerous type of icing that boots can do nothing about is very high. I fly the 738 and even in that clear ice is a massive hazard and must be avoided. Also worth a mention is that in theory the tailplane will ice on it's leading edge before the leading edge of the wing, therefore by the time you see the required amount of ice on the wing to operate the boots (1/4 inch, correct if wrong) the tailplane will have more than double this amount making the boots about as usefull as tits on a fish. Once again the onboard equiptment is only as good as the person operating it.

If ever climbing through icing conditions make a habit of checking for ice every 1000ft in the climb starting with the tailplane because as said above by N714GZ if it does happen it will take seconds to develop not 10mins.

Also she totally discounted and didn't even consider that the autopilot could have been responsible for the uncommanded dives and turns, simply through an electrical fault of some sort. Infact as the wing iced up with the consequent reduction in lift the autopilot would have tried to counter this with nose up trim right up to the limit before disengaging and leaving the aircraft in a dive with no more elevator authority to try and pull out. Once level she re-engaged the a/p not knowing for sure if it had any part to play.

Got the impression towards the end of the clip that the controller was the one flying the aircraft, and doing all the thinking. As also mentioned above for me this would have been downgrade to PAN and "land at nearest suitable airport" and not a "continue 450 miles to the dest" 1 min after declaring an emergency. Pretty poor display all round from this so called "pilot"

Just my few pence worth :)

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Post by mr crow » Sun Dec 07, 2008 7:41 pm

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Last edited by mr crow on Sun Jan 10, 2010 12:37 am, edited 1 time in total.

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