What is Known Icing?

[johntlewis]

Being a CFII with very little actual flying in IMC, I don't have experience with icing. What exactly is "known" icing?

In the AIM it says "Atmospheric conditions in which the formation of ice is observed or detected in flight." (7-1-23). However, this seems to be in reference to PIREP's. So is "known" icing based upon pilot reports?

Further according to 91.527, you cannot fly into known icing conditions, but how can you know if it's actually icing conditions unless you actually fly into it?

I realize that under IFR you cannot even fly into forecast icing conditions (91.527) (b) (1). However, I'm still confused on when exactly icing conditions become known.

[newty]

I just woke up in a dark room in Idaho but I will give it an off the top answer which others can pick apart later. I think Known Icinbg is either reported (PIREPS) or also Forcast Icing can be considered Known Icing as well as anytime that you can reasonably expect ice based on current weather observations. Thats all I got, I'm going back to sleep

[meritflyer]

Threre was a recent interpretation from a FSDO that commented on "known icing" as "visible moisture".

I'll see if I can find a reference.

[meritflyer]

Okay, here it is..

http://www.aopa.org/whatsnew/newsite...1127icing.html

[B767Driver]

In a nutshell....visible moisture (clouds, rain, snow, low visibility) below the freezing level is known icing, and irrespective of forecasts, pireps, etc. They don't mean anything legally.

[meritflyer]

Here is another LOI.

http://www.genebenson.com/docs/icing_exp.pdf

[JEP]

Originally Posted by meritflyer

Threre was a recent interpretation from a FSDO that commented on "known icing" as "visible moisture".

I'll see if I can find a reference.

http://www.jetcareers.com/forums/sho...21&postcount=3

[meritflyer]

Thanks Jep!

You Da Man!

[UAL747400]

The way I remembered it was pireps, sigmets for icing(I think this was more of a go/no-go policy with UND), and visible moisture with temps between -20C and 2-3* above.

Sorry about the vagueness. The thing that sticks out in my head was the lower temp. for known icing. I did my instrument training in ND in the winter and that was the magical number to look for to be less than -20 whenever I had to go do x-countries when the visibility sucked or was snowing.

[johntlewis]

Originally Posted by JEP

http://www.jetcareers.com/forums/sho...21&postcount=3

Wow! I didn't know that snow was considered known icing. I guess I've flown into known icing before cause I've done it several times before. Not anymore, though.

[BeechBoy]

That FAA letter (the one dated June 6, 2006) which states that known icing conditions exist "when visible moisture or high relative humidity combines with temperatures near or below freezing" and which further states that flying into such conditions constitutes a violation "whether or not the aircraft accretes ice or not" is overly restrictive.

Many, many times I've been in clouds with temps slightly below freezing and didn't pick up any ice at all. I fly in known icing conditions ALL THE TIME and, more often than not, the airplane either picks up no ice at all or accumulates such a small amount that it's not even worth blowing the boots.

That being said, I still think it's stupid to fly into known icing conditions without a good plan on what to do if the airplane starts to accumulate ice. If you're airplane has anti-ice/de-ice equipment the plan may be as simple as turning on this equipment. Even if the airplane has no de-ice equipment whatsoever I think you can still safely fly into "known icing conditions" as long as the pilot is willing to return to the ice free air from which he came AT THE FIRST SIGN of ice accumulation. I like Richard Collins' philosophy on ice: treat it like smoke in the cockpit. Do something and do it NOW. Do not wait and hope conditions will improve.

I appreciate you guys sharing this info with me. I learned something new today .

[SteveC]

Pertinent info from Avweb Biz edition this week (January 17th):

Originally Posted by Avweb

Embarrassed FAA Preparing To Overturn "Known Icing" Interpretation?

Sources this week tell AVweb the FAA is preparing to overturn a much-ridiculed June 6, 2006, letter from the agency's eastern region that reinterpreted what constitutes "known icing conditions" by reverting back to guidance initially published in 2003. The letter, by FAA Eastern Region Counsel Loretta E. Alkalay, was written in response to an operator's request for a definition of what constitutes "known icing conditions" and stated, "known icing conditions exist when visible moisture or high relative humidity combines with temperatures near or below freezing." She added, "flying through clouds at an altitude that is near or below freezing would constitute flight into known icing conditions." Since the letter was written last summer and became widely disseminated later in the year, numerous aviation organizations expressed opposition to its conclusion. For example, the Aircraft Owners and Pilots Association (AOPA), in a letter written by Luis Gutierrez, the association's director of regulatory and certification policy, told the FAA its interpretation "would unnecessarily ground many safe general aviation flights and may negatively affect safety because many pilots would not be able to train nor maintain flying proficiency during the winter season." Now, according to AOPA spokesperson Chris Dancy, the association "understands the FAA is preparing to overturn" the June letter in a fashion "consistent with current guidance," although he could not highlight how the FAA's policy reversal might be accomplished. Instead, AVweb has learned the FAA likely will revert to a 2003 definition of "known icing."

When the FAA may act to overturn the Alkalay letter is not known, but it appears the agency may accomplish this feat by publishing official guidance. The "hook" on which the FAA apparently may rely is a May 7, 2003, document that sought to clarify and redefine icing terminology [PDF]. That statement, itself a result of a December 22, 2000, proposal calling "for new and revised icing terms," grew out of the 1996 FAA international conference on aircraft in-flight icing. In its 2003 statement, the FAA defined "known icing conditions" as "[a]tmospheric conditions in which the formation of ice is observed or detected in flight." Which is a far cry from the "visible moisture or high relative humidity combines with temperatures near or below freezing" in the Alkalay letter. In fact, sources tell AVweb it's clear the FAA is rather embarrassed by the regional counsel's interpretation and the effort it will have to expend to overturn her letter and return the known icing definition to what it has been. And those sources reminded AVweb this is not the first time that office overturned well-establish FAA policy. All of which made one observer with whom we spoke wonder: What will it take for the FAA to suggest to Ms. Alkalay that she stop writing letters?

.

[Ian J]

Originally Posted by SteveC

Pertinent info from Avweb Biz edition this week (January 17th):



.

Excellent news!

[DE727UPS]

What a great system we have...

I swear, could the FAA be more inept?

My policy is to have as little to do with those folks as possible (outside of ATC).

[BeechBoy]

I don't understand why the FAA continues to try to regulate something as unpredictable as ice accumulation.

As pilots it is our responsibility to make sure that we don't back ourselves into a corner. This includes ice, fuel, weather, etc.

I think wording to the effect that, "When flying in known or forecast icing conditions the PIC is responsible for ensuring that the airplane remains clear of (or exits) conditions which will seriously undermine aircraft performance" would be most appropriate. This would allow the pilot to legally take a "look see" into the icing conditions while holding him completely responsible for the outcome of said "look see".

[johntlewis]

Leaving "known icing" so vague probably gives the FAA more power to have something against us when they want to say we've done something wrong. They like it that way.

[B767Driver]

I think it's a good interpretation. If you want to fly in potential icing conditions, then buy an airplane that can handle it. If not...then that's one of the huge limitations of a small airplane.

Icing is very esoteric. It can accumulate rapidly then all of a sudden be gone. 2000' above or below you could be ice free...but in the middle moderate. If you are in a small airplane and hit a moderate icing channel, you could accumulate an inch of ice in an instant, well before the time necessary for ATC to move you...if they even can. If the airplane is fortunate enough to maintain altitude, it might survive only to find popped rivets and wringled skin due to the stress of the extra weight when back on the ground.

I've always shook my head in amazement at the decked out C172's out there with the fancy FMS systems...yet, a cold cloudy weather system could keep the airplane out the the IFR system for weeks. Not exactly reliable transportation.

Fly it below the freezing level. (Assuming no temperature inversion!)

[UAL747400]

About the weight of ice. Is it the actually physical weight of the ice, or does it have an aerodynamic effect that makes it seem heavy. I do understand the effect it has on lift and the rediculous amount of drag it adds, but I can't fathom that the ice itself is that heavy. I think I've read somewhere that an inch of ice is around a couple hundred pounds? I've had a half inch on my entire car before, no suspension sag. So is it the physical weight of the ice, or does the aerodynamic effect cause airplane to "feel" the weight of the ice more.

[Andrew_VT]

Originally Posted by B767Driver

If the airplane is fortunate enough to maintain altitude, it might survive only to find popped rivets and wringled skin due to the stress of the extra weight when back on the ground.

Uhh, my BS sensor just went off.

I've never heard of popped rivets of wrinkled skin due to the weight of ice hanging off an aircraft. I would think that that much ice to do this would take the plane down due to aerodynamic reasons long before it got to that point. Are you talking Cessna's here?

[B767Driver]

Originally Posted by Andrew_VT

Uhh, my BS sensor just went off.

I've never heard of popped rivets of wrinkled skin due to the weight of ice hanging off an aircraft. I would think that that much ice to do this would take the plane down due to aerodynamic reasons long before it got to that point. Are you talking Cessna's here?

It's not due to the ice "hanging off of the airplane". If you fly an airplane over it's maximum weight and maneuver at normal envelope levels...the structure may start to deform. I've seen the skin wrinkled at a seam in an Arrow after it came back coated with 3/4 inch of rime ice. The mechanic suspected it was due to the added stress from the weight of the airplane...or possibly a hard landing that ensued during touchdown. This particular airplane happened to continue flying instrument approaches for 90 minutes in icing conditions.

It may add less than 150#, but we should be aware of what happens when you fly an airplane over its weight limit and maneuver toward envelope limits (to include a hard landing).

[NJA_Capt]

Originally Posted by B767Driver

...or possibly a hard landing that ensued during touchdown.

By far the most plausible reason.

Originally Posted by B767Driver

This particular airplane happened to continue flying instrument approaches for 90 minutes in icing conditions.

If this was a CFI (or not) I hope he was reprimanded for POOR decision making! I'm sure the Feds would love for him to explain his (lack of) reasoning.

Originally Posted by B767Driver

...we should be aware of what happens when you fly an airplane over its weight limit and maneuver toward envelope limits (to include a hard landing).

The problem is.....you do not know where the envelope limit IS any longer. When ice accumulates on an airplane, it is not evenly distributed and it is not balanced. You have no idea how a plane will react until it does react. In your Arrow snippet above, he probably landed with full flaps as normal and encountered a tail stall which quickly dropped him to the runway.

PSA: If you are in an unprotected aircraft, do not fly in visible moisture when it is less than 10 degrees C.

[Andrew_VT]

The upper wing skins on the 2 arrows I fly regularly are all wrinkled though....Moreso than any other planes I've seen. I think they just have a propensity for it.

Oh and the hard landing due to early stall (due to the ice affected airfoil) makes total sence.

[mikecweb]

Originally Posted by B767Driver

Icing is very esoteric.

That be one of them big words i don't understand...

[B767Driver]

Originally Posted by NJA_Capt

If this was a CFI (or not) I hope he was reprimanded for POOR decision making! I'm sure the Feds would love for him to explain his (lack of) reasoning.

.

He was canned.