"The least that you need to know"

Public domain image by Donald Cook

Summary

The Basics introduce core concepts and vocabulary of aircraft icing with images, "the least that you need to know".

Discussion

The Basics seek to facilitate initial learning about aircraft icing by:

• focus on the needs of beginning learners
• readily connecting to other resources for further learning
• maximizing reuse
• maximizing access

Other sources may not do these well.

Background

One of the most-read posts that I have written was A Gentle Introduction to Aircraft Icing, so I think that there is interest in this topic.

My learning experience

I got a MSME degree from the University of Wisconsin Internal Combustion Engine lab. That prepared me well for some aspects of aircraft icing (heat transfer, thermodynamics, drop physics, computational fluid dynamics). However, that by itself was not enough.

When I started in an Aircraft Systems design group, it was common practice to hand the new engineer either ADS-4 (483 pages long) or a little later DOT/FAA/CT-88/8 (390 pages for Volume I, plus more in Volumes II and III) to read. This was typically not the right scope for someone new to the field, or efficient. I have re-read those several times, and I always pick up some detail aspects that I did not well appreciate before.

Most engineers eventually (including me, after a few years in the field) went to the week-long University of Kansas "Aircraft Icing: Meteorology, Protective Systems, Instrumentation and Certification" course (yes, it has been taught for decades). This was more effective and efficient. However, it is probably a bit much for an introduction (not everyone needs to know how to calculate the theoretical LWC from a SkewT-LogP chart, for example).

So, there needs to be something other than a 400-page, rather technical document (even if you have an engineering degree) for learners to start with.

Core concepts and vocabulary

I have previously written and taught training classes on aircraft icing.
Learners have been from diverse backgrounds (engineers, meteorologists, administrators).

I have also been on industry committees with more diverse backgrounds.

I have learned the value of having the same core concepts and vocabulary.

(And, if anyone does not think that having common concepts and vocabulary are important, read "APPENDIX A - DISCUSSION OF ICING INTENSITY TERMS DEFINITIONS" from SAE ARP5624, Aircraft Inflight Icing Terminology sae.org [Payment or institutional access required])

So, The Basics will focus on core concepts and vocabulary, with many images to illustrate them.

There are several recognized sources of aircraft icing terms. And that is part of the problem:
there are several, and therefore there are inevitable differences. Beginners cannot be expected to sort out the nuances, or find the few, most applicable terms from a list of 500+ terms.

In keeping with the "least that you need to know" philosophy, approximately 50 terms were selected for the Terminology section from ADS-4 with a few updates (such as "Appendix O").

With the core concepts and vocabulary, you can then be better able to ask questions of experts, and form more productive online search queries.

You can also better determine which areas you want to explore further.

Lots of images

A major short-coming of the "Big Three" resources (ADS-4, SAE AIR 1168/4, DOT/FAA/CT-88/8) is that there are few photographic images, and the images are not well reproduced in the online, digital versions. Images are key for introducing concepts, they are truly "worth a thousand words" (and no one would actually read those extra 1000 words).

So, The Basics are image-rich. All images are Public Domain, so you can reuse them as you choose.

Broad Access and Reuse

There are many excellent resources that are copyrighted. Unfortunately, this may limit access in ways other than just the money required to obtain them.

I worked at some large companies. They had corporate subscriptions and library services through which an employee could get copyrighted material, without direct cost to your accounting department. However, even with rather low "friction" for getting material, it was under-used. In general, each user was expected to get their own copy for use, and that was often even friction to prevent use.

While I am an advocate for the use of the documents published by the SAE AC-9C Aircraft Icing Technology committee (I have been a member of the committee), I feel that the copyright has limited the knowledge of the documents' existence, as well as their use.

After I took the University of Kansas "Aircraft Icing" course, I lugged around the rather massive (about 8 inch thick), two-volume printing of copyrighted material from the course for years. I only looked things up once every two years or so. A digital file or online access would have been far better.

The limits of "fair use" may not be clear in some circumstances. There may be interesting figures that you apparently cannot re-use. Sometimes, the images were originally in the public domain, but are not noted as so. (For example, see "Contending with Airframe Icing".)

This series uses the Creative Commons BY-NC-SA 4.0 license. This allows reuse (the SA or "Share Alike" part, see the license for details.)

The use of online, public domain resources is prioritized. Some selected copyrighted, non-free resources are also noted, where I have not found adequate public domain substitutes.

Online resource

The Basics is an online resource. This allows wide access, at low- to no-cost. This also allows the use of search engines.

Online resources can be readily updated to correct errors, incorporate new information, and expand the scope. The Basics are a work in progress, and may have changes and additions.

However, links to online resources will inevitably suffer "link rot". I have kept similar lists of resources for years. I have tried to select sources that are likely to be stable. Some links from ntrs.nasa.gov have worked for years, and dtic.mil for even longer.

The fate of the "Electronic Aircraft Icing Handbook" is cautionary. An apparently endorsed online resource (mentioned in AC 20-73A faa.gov), it is now only available at web.archive.org.

I do plan to curate the links for a while.

You may find an archived version of icinganalysis.com, including The Basics series, at web.archive.org.

Focus

To keep the focus on learners, The Basics are a largely separate website from "Blast from the Past: NACA Icing Publications" icinganalysis.com. "Blast from the Past" focus more on what was historically done, while The Basics focus on what to do today.

Aircraft icing training classes available

When you have completed The Basics, some more formal training is available.

• University of Kansas "Aircraft Icing: Meteorology, Protective Systems, Instrumentation and Certification" enrole.com

  This course covers the meteorology and physics of aircraft icing. Topics include forecasting, finding and avoiding icing conditions, designing and evaluating ice protection systems, and certification of aircraft for flight into known icing conditions.

• NASA Aircraft Icing Training aircrafticing.grc.nasa.gov

  A course primarily intended for pilots who fly aircraft certified for flight into icing. With an operational focus, this course provides tools pilots can use to deal with in-flight icing.

• "ALC-33: Inflight Icing" faasafety.gov

  Despite improvements in equipment and forecast technique, inflight icing is a contributing factor in accidents and incidents each year. What are the reasons for these encounters, and what can you as a pilot do to safely manage the risk associated with icing?
  In this course you will learn that water does not always freeze at 32° F. or 0° C. You’ll discover which temperatures are most conducive to clear, rime, and mixed icing, and how water content and droplet size relates to icing severity. You may discover that the de-ice or anti-ice equipment on your aircraft cannot always provide adequate protection. You will find tools for evaluating icing conditions before flight, and you'll have the opportunity to understand and learn how to avoid or, if necessary, recover from roll upset and tail stalls caused by structural ice.

Some commercial computational fluid dynamics (CFD) packages that include icing simulation capabilities offer training (I have attended one of them). While these are useful tools, they are a subset of the required knowledge (CFD ≠ Aerodynamics ≠ Aircraft Icing).

Public domain image by Donald Cook

While formal training may be essential for many applications, they are not typically focussed on beginning learners.

Some other introductions

• "Airframe and Engine Icing" ntrs.nasa.gov

  This is both a presented version of NASA's in-flight icing training aids, and a brief discussion of NASA Glenn's two icing-capable facilities that simulate the airframe and engine icing environments.

• "Introduction to Aircraft Icing and NASA's Approach to Understanding It" ntrs.nasa.gov

  This presentation provides an introduction to aircraft icing and describes NASA’s approach to understanding it. The presentation covers various topics on icing. A general overview of different types of icing is provided, which includes airframe icing, jet engine icing, and rotorcraft icing. The presentation discusses NASA’s approach to studying the various forms of aircraft icing, which includes conducting flight tests, performing ground-based icing wind tunnel tests, and developing computational tools that simulate the icing physics. An overview on the future of aviation and icing is provided. The presentation is largely high level, but also provides some technical icing physics discussion.

• "Icing" weather.gov

  Icing, in general, is any deposit or coating of ice on an object, caused by the impingement and freezing of liquid (usually supercooled) hydrometeors; to be distinguished from hoar frost in that the latter results from the deposition of water vapor.

• "Introduction to Icing Certification" faa.gov

  During icing certification potential icing threats are evaluated through analyses and tests to ensure the aircraft can operate safely in icing conditions.

Scope

I have started with a limited scope: "The Basics", which is as an introduction to terms and concepts.

These are written with a "the least that you need to know" philosophy. There are resources listed if you wish to dive deeper into a particular topic.

These assume no prior knowledge in aircraft icing, and require no math skills. They can be read in less than one hour, or presented in two hours.

While The Basics assume little prior knowledge, they assume that you are interested in further learning about aircraft icing. They are not aimed at the general-public.

"Intermediate" topics require mathematics and computer skills. These are in-work, but not yet available:

• Using handbook design and analysis methods
• Using computerized icing analysis tools
• Preliminary ice protection system sizing

"Advanced" topics require more experience and judgement, and I might not get to writing them any time soon:

• Icing Wind Tunnel Testing
• Practical design trade-offs
• Quantifying precision, accuracy, uncertainty, and "goodness"

Topics not included

In-flight icing (only) is covered.

Topics that are specifically not included:

• Icing on the ground
• Piloting in icing weather
• Certification

While the information here may be complementary, for the topics above there is ample formal training available. I believe that there are no conflicts here with that formal training. If there are conflicts, follow your formal training, and please let me know so that I can correct things.

On to The Basics