Light twins and icing conditions

[EGBKFLYER]

A good friend of mine is currently doing his IR on a twin with no de-icing kit. Yesterday, he flew in conditions which resulted in the aircraft picking up some ice (I don't know how much, but his description suggests light to moderate). MSA was above freezing level and cloud tops were to high to get above sensibly.

When my friend questioned the ice build-up, the instructor said it was OK and they should carry on and that my friend should let him know if he was having any control difficulty:ooh:.

I'm quite concerned by this intructor's lack of respect for icing and the method of deciding to get out of it (if they could) - am I showing my lack of experience with non-de-iced light twins or is this instructor a bit of a 'maverick'?

[nick14]

Well personally I would not fly IFR without de-icing/anti-icing kit.

I would be inclined to agree with you, if the a/c picks up ice and has no de-icing kit I would probably get home, unless the instructor is very experienced and im talking rubbish (very possible :}).I would prefer to err on the side of caution with ice.

N

[SNS3Guppy]

Your friend and his instructor may not be with us much longer.

Time to find a different instructor now, should you wish to know your friend at a later date.

[P.Pilcher]

Without being a "fly on the wall" it is very difficult to give any form of definitive answer to this. It is however a fact that instructors and newly qualified CPL's have had little or no icing experience even in aircraft that are certified for flight in such conditions thus it is very difficult to criticise this particular instructor as we do not know how much experience he has had. In his favour the freezing level was above the MSA thus if things did turn really pear shaped, he could have descended (or may have been obliged to) and normal services would have been restored before an encounter with the hard stuff would otherwise have occurred. How light was the dusting? Had he penetrated briefly a wisp of cloud below 0 degrees C and picked up a little dusting, or was he holding or conducting an airways sector in the stuff which was building up continuously. If either of these was the case then he had clearly assessed that the ice build up was sufficiently slow that he would not experience trouble and would in any case melt it off when he descended. As more experienced bretherin will know, even with a fully de-iced aircraft, it is best to keep out of it if at all possible. Expanding boots on leading edges are not always successful and ice invariably builds up elsewhere on the airframe increasing weight, impairing performance and slowing the a/c down. I don't know how many times, in this situation I have said "10 more knots off the airspeed and I am descending to get rid of this!"
No - I would not castigate this instructor as some have, but if he was picking up clear ice from supercooled rain and the 0 degree isotherm was below his MSA, then I would heartily agree.

P.P.

[EGBKFLYER]

Thanks for your replies folks - reinforcing my own view I think. The instructor is apparently a 747 captain or FO, so experience should not be a question (though I don't know what his experience of flying relatively low in small aircraft is).

P. Pilcher - MSA was above freezing level so descent was not an attractive option - this is what made it particularly bad for me. They apparently flew an airways route almost permanently in cloud. It sounds like they were picking up rime - sufficient to alarm my friend when he heard chunks of ice hitting the fuselage from the props...

I've pointed out the CRM aspects of this to him too - he was concerned about the build-up but the instructor said it wasn't a problem so they carried on. At the very least, it's teaching an inexperienced IR student potentially bad/ fatal habits. Quite aside from flying other than in accordance with the AFM.

I've advised my friend to ask that instructor (tactfully) more about his decision and view of icing - it may reveal something that he can either learn from or use as his own reason for not flying with that guy again.

[flightlevel1985]

I have just today finished my IR, and to be honest I would have been worried if any of my flights would have occured in conditions such as those described here. Having seen how quickly even a little shade of ice can build up, I would always personally side on the side of caution...

[BigEndBob]

Even with deicing, ice still has to be respected.
I had an stabilator jam on Seneca doing IR training, -10 @10000'.

Aircraft Icing Training - Courses (http://aircrafticing.grc.nasa.gov/courses.html)

[Duchess_Driver]

I fly IFR without de/anti ice all the time.

Don't recommend it in IMC tho....

[SNS3Guppy]

The instructor is apparently a 747 captain or FO, so experience should not be a question (though I don't know what his experience of flying relatively low in small aircraft is).


So am I...but looking around at the others I work with on a daily basis, I'd recommend you don't place a lot of faith in an instructor simply because he flies a 747. A 747 isn't a Seneca, doesn't have piston engines, has considerably greater capabilities in ice, has substantially higher capability following an engine or system failure, and unlike the Seneca, lands a whole lot higher in the air. Trying to go between the two is a good way to get hurt if one isn't fully prepared. I know a number of 747 pilots I'd happily fly with in a big airplane, but wouldn't trust to fly my dog in a light airplane.

No - I would not castigate this instructor as some have, but if he was picking up clear ice from supercooled rain and the 0 degree isotherm was below his MSA, then I would heartily agree.


Whether the aircraft was in supercooled rain isn't a necessary factor to consider the original posters comments. The aircraft was cited as being flown in moderate ice. The next step past moderate is severe, and by definition severe means the ice is beyond the capabilities of the airplane to remove or control it.

The example set is a poor one. Anti-ice in a light twin exists for one reason only, and that reason is not to allow it to fly in the ice. It's to get it out of the ice.

I once sat through a ground school for the Twin Commander, in which the chief pilot asked who knew how much ice the TC could handle. None of us had an answer, so he announced with some certainty that the airplane could handle all the ice one could throw at it, and would lose only fifteen knots.

A few days later we were returning from a desert location to a mountain location, and were climbing IFR and IMC below the MEA. We were in an area of rapidly rising terrain, which was forcing a considerable amount of moist air upward. We hit the icing about the same time we were cleared to the MEA. In one minute over an inch of ice built, and we lost 50 knots. The airplane passed through blue line, then approached redline, and was descending with full power, with full heat and boots, and no sign of improvement.

ATC finally kicked us loose because we couldn't make the MEA at that point, were descending, and out of radar contact. We continued to descent until we made ground contact, close to dark, and were able to reduce the descent rate coincident with terrain, until we reached a rural airport. While that was going on, the sound of ice coming off the props and hitting the cutline behind us sounded like 12 gauge shotguns going off continuously.

The next morning we were called into the owner's office and asked what the holes were doing in the side of his airplane. We went out to the fuel pumps where the airplane was chocked, and found what we hadn't seen in the dark; considerable damage done to both sides of the airplane.

A few days later, I heard the same chief pilot tell someone that sure enough, the airplane could take all the ice one could throw at it...and lose just 15 knots.

Just not true. Airplanes ahead of us on the same routing didn't get the ice, and behind us. We pased through an area of significant ice build-up due to orographic lifting. Ice can build quickly beyond the capability to control, and should be given a great deal of respect. It doesn't take a lot of ice before you're flying an entirely different airplane...different performance, different characteristics, different capabilities. It can become adverse.

Ice shouldn't be taken for granted. Anti-ice systems shouldn't be taken for granted. Build up some ice, blow one boot and have the other fail, and now you have an assymetrical airfoil with two different lift capabilities and handling...on different sides of the airplane...and you're now a test pilot.

Especially in a training environment, playing with ice is a very foolish thing to do, or to show to a student. Particularly in a light twin.

Two years ago I had occasion to take an assigment in a light turobjet airpalne that required carrying about 3" of ice all the time, and maneuvering it to the lower performance limits (shaker and buffet) regularly. Several different times I found unforecast, unadvertised adverse handling characteristics in the airplane. This is not desirable. This is not something you want in training, nor in an airplane with limited performance, nor an example or habit to be developed.

The instructor who perpetuates this hazard does no one any favors.

[nick14]

Just a thought,

isnt it against the law to take an aircraft, which has no anti/de-icing, into known icing conditions?

N

[what next]

Good morning!

isnt it against the law to take an aircraft, which has no anti/de-icing, into known icing conditions?

Of course it is. In addition to "the law" the rules stated in the training manual of the flight training organisation have to be respected, which usually are even more conservative than what "the law" requires. For example, ours require twice the legal minima for ILS approaches (400 ft ceiling instead of 200, 1100m RVR instead of 550). And of course, they state: "no icing conditions".

But reality is not only black or white, as we all know. In our part of the world, avoiding icing conditions at all cost would mean to suspend flight training between Ocotber and April. So the final decision about wether to fly or not to fly will always be based upon the judgement and the experience (and to some extent the courage...) of the instructor. I have learned my lesson many years ago when our Seminole became nearly uncontrollable within less than two minutes due to (unpredicted!) icing - the only time in 30 years of flying when I had serious doubts if I would make it back home in one piece.
So for me, forecast or observed (or even suspected!) icing below MRVA is a strict no-go criterium. But sometimes it can be a bit embarassing to tell the student (who has taken the day off and driven all the way to the airport) "sorry, but we can't fly in these conditions" while some colleagues or competitors go flying nonetheless...

Greetings, Max

[Pace]

I Have over 2000 hrs in Seneca fives so know them reasonably well. These are certified into light icing. I note the poster reported moderate ice. Was this infact moderate or his interpretation of moderate?

For me icing is a scary thing and that comes from experience of having been dripping in the stuff and getting away with it but through that experience I am much more cautious.

One occasion was flying up to Inverness. There was a line of storms crossing Scotland from West to East.

Moving up from the South I was flying airways on top of a solid overcast so that I could eyeball a way through the line of storms ahead. The solid overcast tops kept increasing in altitude. I was then held At FL110 and entered the clouds with a fairly rapid build up. I selected prop heat on and kept an eye on the buildup. I asked for a further climb and was cleared to FL130.

The climb rate was poor and there was a slight vibration.

On top at FL130 unbeknown to me there are three wires which serve the electrical heating on the props and these had sheared which meant there was no anti ice on the left prop( The shearing of the wires was a known problem and later fixed by a Piper approved mod)

The Seneca has counter rotating props and a very large chunk of ice flew off the left prop. It must have projected forwards as the chunk of ice flew across the nose and hit the right prop.

The right prop hurled the chunk of ice into the side of the nose where it punctured a hole and then flew back into the screen disintegrating into a snow storm. I made it into Inverness where it was disovered that the ice had bent one of the three right prop blades.

The above although a complete fluke is totally true.

Icing is a real danger and something not to mess with especially in a light twin deiced/anti iced or not.

Use the deice/anti ice to get out of it not to cruise in it and if controllers wont let you climb or descend get bossy and explain your situation clearly.

Also beware of days when you know you will carry that ice to the ground Its not quite the threat if you know you can loose a few thousand feet and be in warm air still safely above the MSA.


Pace

[bookworm]

I Have over 2000 hrs in Seneca fives so know them reasonably well. These are certified into light icing. I note the poster reported moderate ice. Was this infact moderate or his interpretation of moderate?

Is there a definition of 'moderate' that doesn't have a highly subjective metric?

It is implicit in the definition of "light icing" that brief exposure is not a "problem":
The rate of accumulation may create a problem if flight is
prolonged in this environment (over 1 hour). Occasional use of
deicing/anti-icing equipment removes/prevents accumulation. It
does not present a problem if the deicing/anti-icing equipment is
used.

But for "moderate icing"
The rate of accumulation is such that even short encounters
become potentially hazardous and the use of deicing/anti-icing
equipment or flight diversion is necessary.

So what do you do in an aircraft with de-ice that is "certified into light icing"? Does the de-icing suddenly stop working after an hour? If it can cope with the ice by use of the available equipment, is it "light" or "moderate"?

A History and Interpretation of Aircraft Icing Intensity ... (http://www.tc.faa.gov/its/worldpac/techrpt/ar01-91.pdf) has some very interesting perspective.

[Pace]

Bookworm

So what do you do in an aircraft with de-ice that is "certified into light icing"? Does the de-icing suddenly stop working after an hour? If it can cope with the ice by use of the available equipment, is it "light" or "moderate"?

It is not just the ability of the boots to kick off ice or the prop heating to keep the props reasonably clear.

Ice will be accumulating all over the airframe not just the leading edges and props.

The airflow will be disrupted and the aircraft will also be carrying more weight.
The props even anti iced will not produce as much thrust.

Even keeping your boots clear you will note a drop off in IAS at cruise speed and a further drop as more ice accumulates on the airframe.

The stall speed will increase so your cruise speed decreases and your stall speed increases coming closer together.

On a light twin or single becuase the initial cruise speed isnt high the stall and cruise will get closer and closer.

So its not just about accumulating light ice and the deicing anti icing being able to cope with it but the continued accumulation on all the services not covered by anti ice or deice over longer periods or greater accumulations.

As the speed decays to maintain altitude the greater angle of attack and increased drag from that.

Also as the airflow descreases so does the friction from the airflow. As the angle of attack changes so does the point of ice accumulation on the lifting surfaces.

At that point I will let someone with greater knowledge of flight dynamics take over especially regarding ice accumulations :)

Pace

[waren9]

Quote from the very first post......

When my friend questioned the ice build-up, the instructor said it was OK and they should carry on and that my friend should let him know if he was having any control difficultyhttp://static.pprune.org/images/smilies/icon25.gif.


Its a bit late by then, isnt it?

[SNS3Guppy]

Yes, it certainly can be.

[bookworm]

It is not just the ability of the boots to kick off ice or the prop heating to keep the props reasonably clear.

This is all true Pace, but I was just highlighting (obviously not very clearly) the absurdity of the definitions.

Moderate icing is defined as a level of icing that necessitates de-icing equipment. It really doesn't make sense to have certification of de-icing equipment for "light icing". If the equipment is necessary and can cope with the conditions, the icing is "moderate". If it can't cope with the conditions, the icing is "severe".

[Pace]

Intensity Aircraft Ice Accumulation
Trace Ice becomes perceptible. Rate of accumulation slightly greater than rate of sublimation. It is not hazardous even though deicing/anti-icing equipment is not used unless encountered for an extended period of time (over 1 hour).
Light The rate of accumulation may create a problem if flight is prolonged in this environment (over 1 hour). Occasional use of deicing/anti-icing equipment removes/prevents accumulation. It does not present a problem if the dicing/anti-icing equipment is used.
Moderate The rate of accumulation is such that even short encounters become potentially hazardous and use of deicing/anti-icing equipment or diversion is necessary.
Severe The rate of accumulation is such that deicing/anti-icing equipment fails to reduce or control the hazard. Immediate diversion is necessary.

I cannot take your description of icing categorisation in total because light, moderate, or severe would be aircraft specific ie a Boeing 777 would deal with far more icing than I light twin. So icing has to be categorised more by rate of accumulation than by aircraft ability to deal with it. If that was the case icing reports would Vary. ie moderate to a 777 pilot may be severe to a light twin pilot which obviously is not the case in PIREPs

I believe the below is your description

Moderate icing is defined as a level of icing that necessitates de-icing equipment. It really doesn't make sense to have certification of de-icing equipment for "light icing". If the equipment is necessary and can cope with the conditions, the icing is "moderate". If it can't cope with the conditions, the icing is "severe".

Pace

[SNS3Guppy]

If that was the case icing reports would Vary. ie moderate to a 777 pilot may be severe to a light twin pilot which obviously is not the case in PIREPs


Actually, that is precisely the case. One must ALWAYS consider the source aircraft reporting the icing, as the nature of what is being reported is VERY aircraft-dependent.

Severe icing is always icing that exceeds the ability of the airplane to contain or remove the ice accumulation; it's ice beyond the specific airplane's capabilities to handle the ice.

Icing reports do vary; absolutely icing reports vary. This is ALWAYS the case with PIREPS. Moreover, the nature of what's reported is subjective according to the individual experience level of the pilot. What is light to one pilot may be moderate to another, even in the same type aircraft. What is light in one type aircraft may be moderate or severe in another type aircraft.

[Pace]

Moderate-severe. 0.75. Moderate. 0.625. Light-moderate. 0.5. Light. 0.375. Trace -light. 0.25. Trace. 0.125. No icing. 0. Definition. Severity Index

Icing reports do vary; absolutely icing reports vary. This is ALWAYS the case with PIREPS. Moreover, the nature of what's reported is subjective according to the individual experience level of the pilot. What is light to one pilot may be moderate to another, even in the same type aircraft. What is light in one type aircraft may be moderate or severe in another type aircraft.

SN3Guppy

Surely the categorisation of icing severity HAS to be based on the rate of accumulation and not the ability of a specific aircraft to deal with ice accumulations? I appreciate a pilot report on icing is subjective as in turbulence reports.

Pace

[bookworm]

Surely the categorisation of icing severity HAS to be based on the rate of accumulation and not the ability of a specific aircraft to deal with ice accumulations?

Should be? Yes. Is? No. Not yet at least. The link I gave above makes that very point.

[SNS3Guppy]

Surely the categorisation of icing severity HAS to be based on the rate of accumulation and not the ability of a specific aircraft to deal with ice accumulations? I appreciate a pilot report on icing is subjective as in turbulence reports.


Absolutely not.

Icing severity is very much aircraft dependent. Icing severity in flight is a Pilot Report (PiRep) function, and is always subjective.

The amount of ice which accumulates depends on the aircraft structure, type of protection, etc. One airplane may be accumulating very little ice, while an airplane flying along side it may be experiencing severe icing.

Severe icing is that icing which is beyond the capability of the airplane to handle the conditions or the ice. Trace ice to one airplane may be severe to another.

I've operated during weather research flights in conditions which produced 3 inches of ice buildup. If you experienced this in many aircraft you would be unable to remove it, you would experience significant weight and aerodynamic penalties, and might very well consider it severe icing. So long as we could operate in those conditions and our ice protection kept our critical surfaces clean, we kept flying, and in fact sought out the maximum icing rate we could find.

By most accounts, that level of icing would be severe. For us, it was not.

Icing is always subjective. Furthermore, a change in the capability of the airplane may change a moderate icing condition to a severe one with no change in the amount of ice or the rate of accumulation.

I experienced a very significant buildup of ice in a large four engine radial powered airplane some years ago, with large horns or walls of ice extending off the top and bottom of the leading edge, into the slip stream, some eight inches or more. Strange looking twisted tentacles built forward into the slipstream off the propeller domes. The aircraft was controllable, but we evaluated our options. We were in the process of requesting a change and making that change when I began to experience aileron snatch with the controls attempting to jerk to the right. We descended only about 3,000' before much of the ice shed from the wings and the control issue immediately ended.

One could easily say that such a level of ice constitutes a "severe" buildup. It was definitely severe icing, and rapidly exceeded our ability to remove it, and then immediately thereafter, to control the airplane. This took place in a very short period of time. However, it's noteworthy that up until the aileron snatch was experienced, no adverse control effects were observed...quite likely this would have been severe ice much earlier for some airplanes, but this airplane remained controllable much farther into the icing process. We had no intention of seeing how far it would go; the ice buildup occured while we were maneuvering to get clear of the icing conditions. Ice, the rate of buildup, how it builds up, the type of icing, etc, affects different airplanes in different ways.

Ice that is melted off the leading edge of a wing but runs back and refreezes may represent a severe icing condition to that airplane, but not to other airplanes in the same area, experiencing the same conditions.

Icing is very much relative. One cannot make an assumption that any report of icing as trace, light, moderate, etc, represents the true icing conditions that one can expect to experience. Simply because that's what the other guy got...should never be taken on assumption to indicate what you might experience. One man's ceiling is another man's floor, and the same applies to aircraft. What's light to one can easily be severe to another.

[Bittair3000]

I remember an instructional video that said if you encounter ice buildup which is too much for comfort you can escape it by changing your altitude 3000 feet up or down.

Anyone else familiar with this theory?

[SNS3Guppy]

This is sometimes the case, sometimes not.

If you're close to MEA over mountainous terrain, quite possibly not.

The two greatest buildup conditions are either freezing rain with supercooled water droplets, or large supercooled water droplets near the -10 deg C range. A descent of 3,000' in either case may not be possible, and may not get you out of the ice; a climb likewise may do little to protect you.

The nature of the conditions determine your options. If you're in a layer and icing up, you may well simply be able to climb or descend out of the layer. Icing is commonly found greatest in relatively narrow bands...but one should never count on that. Further, even if one stops the ice buildup, one may be stuck with what's on the airframe and be unable to shed it.

Know in advance where your best prosepcts lie for escaping icing conditions. Know where the freezing level is, the extent of visible moisture or precipitation, and look over lifted indexes, pilot reports of ice, etc. This should always be a primary consideration, especially in a light airplane, remembering that your ice protection isn't there to allow you to stay in the ice, but to get you out of the ice. Plan accordingly.

[scooter boy]

SNS3Guppy, sound advice :D.

I fully agree that the deicing is a get-out-of-jail-free-card.

Crossing fronts in IMC is where I have seen really rapid acculumations (centimetres in seconds) which I suppose has been freezing rain (looks like sleet from inside the cockpit until you lose forward vision). This is almost always in or around moderate turbulence and I am careful to not allow the aircraft to accelerate while descending to get rid of the ice but equally try to keep the speed from dropping too low in order to avoid tail stall. I think these are about the most challenging flight conditions that I have encountered.

Ice scares me and I do my best to avoid it, no deicing system can handle bad icing.

SB

[Pace]

I would add to the excellent information from Guppy to also be wary of flying in conditions where you know you will hold ice to the ground or the MSA.

I can remember a trip in a light twin where I had encountered a lot of ice airways. I left the weather but still had a long way to go.

The speed had decayed so much that I asked the controllers whether I could descend below the airway for Ten minutes so that I could melt it all off the airframe.

I then climbed back up and setup a normal cruise.

Some ice will vapourise off once clear of ice and cruising but you can carry a substantial amount of airframe ice.

On another trip into Scotland I could hear large jets reporting ice in the holds and on approach. I was then given a descent to take up a hold. I delayed that descent for as long as possible to keep in clear air on top. Descending into the clouds into the hold it quickly became apparent that unlike the larger aircraft I could not hold for very long. Do make it clear to controllers if they ask you to do something which will cause problems.

Ice can be scary because it is inconsistant, can take you by surprise and can build very quickly. In larger aircraft which climb at 3000 fpm you can quickly climb through those ice layers. In light singles or twins you hang around in there with aircraft which are least equipt to deal with it.

Pace

[Vee1Kut]

Something tells me the instructor wasn't worried about the icing....

[EGBKFLYER]

Dear All

Many thanks again for your valuable input - my friend has read this thread and learnt from it (as have I).