Icing intensity definition

[hais]

I was looking at Garmin Pilot intensity scale and started wondering, what is "extreme icing"? 

Appears there is no definition of that according to this FAA.

I wonder what is the point of that additional scale since we are not allowed to fly into known severe anyway - and SLD is already separately coded. 

[M20F]

Icing conditions are airframe specific, the world as much as we would like it to be is not blacks and white always. 

[A64Pilot]

Not being an ice pilot, I believe severe icing overwhelms the anti / de-icing equipment, and severe means continued flight isn’t possible, meaning stay in it and you will have a negative outcome pretty quickly , regardless of how your equipped.

A lot like turbulence, most talk like they have been in severe or extreme turbulence, but thankfully most haven’t, not really.

Severe is so bad you will occasionally lose complete control and possibly bend the airplane, extreme adds in frequent total loss of control and likely airframe damage, up to undergoing rapid disassembly.

Thankfully I’ve never really been close to either.

Both Turbulence and icing are very airframe dependent, my no ice equipped J can’t handle near the ice a FIKI airframe can. so severe to me is likely light to them, an Airliner it’s assumed can handle much greater turbulence than we can etc.

[hais]

11 hours ago, M20F said:

Icing conditions are airframe specific, the world as much as we would like it to be is not blacks and white always. 

I thought PIREPs are airframe dependent, but forecasts are based on airframe-independent rate of accumulation.

[hais]

9 hours ago, A64Pilot said:

Not being an ice pilot, I believe severe icing overwhelms the anti / de-icing equipment, and severe means continued flight isn’t possible, meaning stay in it and you will have a negative outcome pretty quickly , regardless of how your equipped.

A lot like turbulence, most talk like they have been in severe or extreme turbulence, but thankfully most haven’t, not really.

Severe is so bad you will occasionally lose complete control and possibly bend the airplane, extreme adds in frequent total loss of control and likely airframe damage, up to undergoing rapid disassembly.

Thankfully I’ve never really been close to either.

Both Turbulence and icing are very airframe dependent, my no ice equipped J can’t handle near the ice a FIKI airframe can. so severe to me is likely light to them, an Airliner it’s assumed can handle much greater turbulence than we can etc.

That explains Severe. Not sure still what "Extreme" is. The scale they have is "Trace", "Light", "Moderate", "Severe" and "Extreme". The first 4 are defined by FAA, the last apparently not. 

Reading the document, I was surprised that unprotected airplanes are allowed to fly into known trace icing. 

[M20F]

10 minutes ago, hais said:

I thought PIREPs are airframe dependent, but forecasts are based on airframe-independent rate of accumulation.

Page 3 of the document referenced in the first post.  

[hais]

4 minutes ago, M20F said:

Page 3 of the document referenced in the first post.  

That was the old definition. The revised definition took care of that, but left open the problem of how the pilot would determine the impact to their airframe.

So rather than "what happens when deicing equipment is used in which interval", the definition now is about how long it takes for icing grow by specific inches. 

[aviatoreb]

43 minutes ago, hais said:

That explains Severe. Not sure still what "Extreme" is. The scale they have is "Trace", "Light", "Moderate", "Severe" and "Extreme". The first 4 are defined by FAA, the last apparently not. 

Reading the document, I was surprised that unprotected airplanes are allowed to fly into known trace icing. 

Is it define by the order?  Trace<Light<Moderate<Severe<Extreme.  Anything beyond Severe is called extreme?

[A64Pilot]

51 minutes ago, hais said:

That explains Severe. Not sure still what "Extreme" is. The scale they have is "Trace", "Light", "Moderate", "Severe" and "Extreme". The first 4 are defined by FAA, the last apparently not. 

Reading the document, I was surprised that unprotected airplanes are allowed to fly into known trace icing. 

I messed up, the second severe was meant to be Extreme. So I meant Extreme means continued flight isn’t possible

Actually that’s a SWAG as I believe Extreme icing isn’t defined, not by the FAA anyway so I guess Garmin could mean anything they want to.

Another SWAG is they didn’t realize Extreme icing was an undefined term as Extreme turbulence does exist and they just put it in there

They made a mistake, maybe

[hais]

Does ForeFlight also has "Extreme"? Could be the data source they are using. 

[Pinecone]

I have simplified the scale.  Two levels

Light - I am OK, not a bother, have an out.

Extreme - Anything above Light.

 

[Scott Dennstaedt, PhD]

You will hear ATC use "extreme" as a level of icing intensity, but there's no such definition for it.  Severe is the maximum since it defines the situation where the ice protection system on the aircraft cannot keep up with the amount of ice that is accreting. Extreme turbulence...yes...extreme icing...no. On the various icing analyses and forecasts, the term heavy is used instead of severe. Severe is reserved for how the airplane reacts to the meteorological conditions, not the meteorological conditions themselves.    

If you are a student of history, an update to the AIM on February 9, 2012 in section 7-1-21 added Heavy to the way pilots should report ice...they said, 

This change addresses the change to the icing intensity definitions, quantifiable icing rates, and an updated replacement for current terminology. It would also help satisfy NTSB Safety recommendations A­96­51 and ­060.

The interesting thing is that they also removed Trace as a pilot-reported intensity. Here's what it ended up looking like...

1. Light. The rate of ice accumulation requires occasional cycling of manual deicing systems** to minimize ice accumulations on the airframe. A representative accumulation rate for reference purposes is 1/4 inch to one inch (0.6 to 2.5 cm) per hour (See TBL 7-1-7)  on the unprotected part of the outer wing. The pilot should consider exiting the condition.

2. Moderate. The rate of ice accumulation requires frequent cycling of manual deicing systems** to minimize ice accumulations on the airframe. A representative accumulation rate for reference purposes is 1 to 3 inches (2.5 to 7.5 cm) per hour (See TBL 7-1-7)  on the unprotected part of the outer wing. The pilot should consider exiting the condition as soon as possible.

3. Heavy.  The rate of ice accumulation requires maximum use of the ice protection systems to minimize ice accumulations on the airframe. A representative accumulation rate for reference purposes is more than 3 inches (7.5 cm) per hour (See TBL 7-1-7)  on the unprotected part of the outer wing. Immediate exit from the conditions should be considered.

4.  Severe. The rate of ice accumulation is such that ice protection systems fail to remove the accumulation of ice and ice accumulates in locations not normally prone to icing, such as areas aft of protected surfaces and any other areas identified by the manufacturer. Immediate exit from the condition is necessary.

But in the very next update to the AIM, they abandoned this approach and went back to the way it is today.  Ugh!

[carusoam]

Hey Dr. Scott is in the MS Hooooouuuuuse! 

Thanks for sharing your weather wisdom again!

Getting ready for the cold that is creeping in….

Go EZWxBrief!

Go MS!

 

Best regards,

-a-

Edited November 7, 2022 by carusoam

[Scott Dennstaedt, PhD]

44 minutes ago, carusoam said:

Go WeatherSpork!

Well, ummm, you mean Go EZWxBrief?

[carusoam]

15 hours ago, Scott Dennstaedt, PhD said:

Well, ummm, you mean Go EZWxBrief?

Oops, my bad!

I even googled it to make sure I got it right…

Now, I have to go back to relearn cut and paste 101….   

Best regards,

-a-