Scott Dennstaedt, PhD

Yes! Having trained thousands of pilots over the last 25 years, the lack of knowledge is likely the biggest reason pilots make poor preflight and inflight decisions. I am not saying that experience is useless, but often risk is addictive. Pilots often gain the wrong experience and use previous successes as the reason for their next go decision. Just because that 3,000 ft stratocumulus deck that they climbed through over the last 10 times resulted in little or no ice accretion, doesn’t mean it’ll be the same on the 11th try. Turns out that the air was much cleaner on the 11th go which resulted in SLD in the climb nearly killing a pilot. He reached out to me to learn why. He learned a ton and now has knowledge to make a better decision-experience alone did not serve him well. Knowledge combined with experience (applied knowledge) is extremely valuable.

That’s correct. Anything with a high radius of curvature allows for efficient ice accretion. So ice accretions themselves make efficient ice collectors.

I do. I wrote this blog post a while back, but it still has relevance for this topic today.

KGAI 272156Z AUTO VRB04KT 1 1/4SM BR OVC002 11/11 A2945 RMK AO2 SLP987 T01060106 KGAI 272128Z AUTO 18003KT 1 1/4SM BR OVC002 11/11 A2945 RMK AO2 KGAI 272121Z AUTO 14006KT 3/4SM BR OVC002 10/10 A2945 RMK AO2

When I was based in Baltimore, I did a lot of flights to GAI including dozens of instrument approaches in actual IMC. Always said that it was just a matter of time before someone hit those power lines. I just don’t see how anyone survived this, much less two people and that nobody on the surface was injured or killed.

Well, ummm, you mean Go EZWxBrief?

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!

Thanks! Personally when I want to really see all the details of the radar depiction I use the Radarscope app. That way I can see the velocity data as well as the Dual Pol data. Gust fronts, outflow boundaries, microbursts, etc. all show up nicely on this app. Caught this microburst from the TDWR near Charlotte the other day with some pulse-type convection in the area. https://www.instagram.com/reel/Cg2rbsqM9i0/

pileus clouds

Back in March 1997, the FAA changed the rules for the classification of major airlines so that air carriers with 10 or more seats, which previously were handled under Part 135 operations, would now be handled under Part 121 operations. Yes, certainly agree that excess thrust, fast climb rate through icing conditions and spending most of the time in temps of -50°C or colder limits exposure. Possibly, but not likely. While none of these aircraft are certified into SLD, they operate under a waiver so they are allowed to fly through large drop icing environments. Again, the biggest threat for these aircraft are ground icing.

Hi Erik, Yes, there have been more twin turboprop icing accidents...I just listed two of them that created the need for better icing forecasts. But for turbofan aircraft, you just don't see in flight issues as it relates to airframe icing. High ice water content (HIWC) yes (e.g., Air France), but not airframe ice. I had a chance to visit the NASA ice house in Cleveland about 7 years ago. In talking with Kurt Blankenship who is a research pilot and deputy of aircraft operations at the Glenn Research Center, the Colgan Air accident had little to do with icing. In fact, on March 25, 2009, NTSB investigators indicated that icing probably did not contribute greatly to the accident. Kurt said that, “the plane basically trimmed itself to a stall. It had a stick pusher on it which he [the captain] fought against and pulled back and held it until the plane finally went over and it was too late.” Could it be that the captain thought he was experiencing an ice contaminated tailplane stall (ICTS) even though he said nothing on the tape? In Kurt’s opinion he thinks “the pilot simply panicked.” Kurt further commented that “he was low to the ground and it [pulling back on the controls] was a natural reaction.” Other mistakes were made such as the co-pilot retracting flaps without it being called and not having a sterile cockpit during the approach to land. From Kurt’s view, this accident “was a low-speed awareness issue and that should be the focus of the training...and recognizing where you are at in the [power curve] regime. They were slow, it was a wing stall, clearly.”

Actually we don't see in flight icing taking down airliners (e.g., turbofan aircraft). Sure, there have been *ground* icing issues (e.g., Air Florida in D.C.) and aircraft sliding off of slick runways, but given the bleed air systems on these aircraft, it's hard to find an icing environment that is problematic while in flight. The in-flight issues have been with smaller twin turboprop commuter aircraft such as the one in Roselawn, Indiana in 1994 and Monroe, Michigan in 1997.

Thanks...however, that domain is being retired at the end of the year.

Agreed that the TKS system has some distinct advantages. I was interviewed by CAV many years ago that you can read here. However, every certified ice protection system has only been certified for penetration into small drop icing scenarios. It is the large drop environments that are the dangerous to these aircraft. Unfortunately, the ones that most pilots are taught about in their primary training are actually the exception, not the rule. What I see is that the definition of "realistic" has an unfortunate bad side to it. No pilot would turn and head toward a supercell thunderstorm on purpose...but it's not the supercell storms that are likely to bite you. It is the benign-looking low-topped convection that is the biggest threat to aviation. A typical rain shower is the threat I worry the most about. Yes, I have a lot of learning yet to do in this area.

Here's today's video... https://youtu.be/OB4mu8VFQZ8

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A different question would be, "at what point does the disfiguring of the airfoil take over before the weight becomes an issue?" Essentially, you can expect to start to develop issues controlling the aircraft due to the increase in stall speed and drag vs the increase in weight on the leading edge. Most of the icing incidents and accidents occur when the angle of attack increases...this means changing flap configuration, climbing or increasing/decreasing power. This doesn't happen because of weight.

That was a clear case of non-classical SLD.

Weight is usually not an issue with airframe ice unless you are accreting it on all aircraft surfaces (e.g., freezing rain). Leading edge ice which is the most common (and why certified ice protection systems area located there) will usually only add 50-100 lbs to the overall gross weight. It is the disfiguring of the airfoil and increase in the stall speed that is the biggest concern. Drag slows you down and eventually your "new" stall speed and airspeed meet up.

Just to point out that there's some bad or incomplete guidance in this article.

Are you flying to AirVenture this year? If so, you might want to watch my Daily Weather Roundup starting on Monday, July 18th to provide a brief daily weather overview for pilots who are planning to fly to Oshkosh or surrounding airports. I will be live on YouTube at 3 pm EDT each day through Saturday, July 23rd. If you cannot attend live, this will be recorded and available on my YouTube channel shortly after the broadcast ends. This broadcast will be in addition to my Daily EZ Weather Brief program I am broadcasting live Tuesday through Friday at 7:20 am EDT. If you are attending, please stop by the SiriusXM tent Monday through Thursday to say hello or attend one or more of the five presentations I'll be giving that week. Click here to view my forum schedule.

If you could not attended last night's webinar, you can view the recording here.

Yep...as I mentioned above, "If you cannot attend the Webinar live, it will be recorded and available on YouTube at a later time."

EZWxBrief has partnered with Lightspeed Aviation, SiriusXM and the Ninety-Nines to give a free Webinar entitled, East coast weather flying during the warm season presented by Dr. Scott Dennstaedt. The Webinar will begin at 8 pm EDT on Wednesday, June 29th. To register, please visit https://siriusxmcommunications.com/aviationwebinars. Once registered, a confirmation email will be sent to you to learn how to sign up to win a Lightspeed Aviation headset that will be given away to one lucky attendee at the end of the Webinar. You must attend the live Webinar to win! Time is running out, so get online today and reserve your virtual seat to this educational webinar about weather. If you cannot attend the Webinar live, it will be recorded and available on YouTube at a later time.

Sure. The point is that with the same EDR values the different airframes the passengers and crew are likely to experience turbulence in a different way. So, while it won't be easy to drink your coffee without spilling some in seat 14B with an EDR value of 38 in the B737 (moderate), most of the coffee would likely end up on you in the M20R (severe).