Articles with tag: "Appendix C"

1. Conclusions of the Series on Dr. Jeck

   "... to illustrate the possibilities" ¹

   
   Public Domain image from DOT/FAA/AR-00/30.

   Introduction

   Dr. Jeck was described as "A gifted physicist and innovator" ². We have seen several examples in this series. Several of his proposals have been adopted, while others are still open possibilities.

   Dr. Jeck's own summaries

   Here are selected conclusions from three of Dr. Jeck's later works:

   "Icing Design Envelopes (14 CFR Parts 25 and 29, Appendix C) Converted to a Distance-Based Format ¹:

   The methods illustrated here provide the icing practitioner with straightforward, understandable, and meaningful ways to document, compare, and evaluate data on icing conditions. They offer a set of working standards for achieving consistency and uniformity among users. Some methods may be more useful than others, depending on the application, but a variety are offered, with examples, to illustrate the possibilities.
   The example graphs also illustrate the use of computerized spreadsheet software for …

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2. Using the Supercooled Cloud Database

   "The confidence in the curves is strongest where the data points are plentiful."¹

   

   Introduction

   With over 6,000 measurements and 28,000 nmi of natural icing flight test data, there are many analyses that can be performed.

   Here, I will attempt to reproduce some of the Natural Probability curves.

   Files provided for the SCDB

   I will refer to Dr. Jeck's published values as the Supercooled Cloud Database or SCDB.

   The database files I received I will refer to at the spreadsheet or spreadsheets.

   There are area where they are not exactly the same, as will be shown below.

   I requested a copy of the SCDB from the FAA, and was provided with a copy. It came as two spreadsheet files, "Convective Cloud Icing Events_original.xls" and "Layer Cloud Icing Events_original.xls". There is only one sheet per file, and no macros, so these are essentially rows and columns of …

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3. Working with Natural Probabilities

   "A number of potential uses are illustrated for the new format, particularly for comparing icing test exposures to ... natural probabilities of occurrence."

   
   Public Domain image from DOT/FAA/AR-00/30. ¹

   Introduction

   In DOT/FAA/AR-00/30 ¹ Dr. Jeck wrote of Figure 23:

   3.2 COMPARING WITH NATURAL LWC PROBABILITIES.
   ...
   Figure 23 shows a set of LWC probability curves derived from about 23,000 nmi of flight data in stratiform icing conditions. Any given curve indicates the probability that randomly encountered, stratiform icing conditions will have an average LWC somewhere below the curve. For example, the 50% curve means that half of the LWC averages will lie below the curve and half will lie above it. The 90% curve means that 90% of all LWC averages can be expected to lie below it, for any given averaging distance, or horizontal extent.

   The sample LWC trace has been plotted on …

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4. Natural Probabilities

   "what is the probability of finding such a test exposure in nature?"

   
   Public Domain figure from DOT/FAA/AR-00/30.

   Introduction

   A 28,000 nmi database is large enough to calculate meaningful probabilities, which Dr. Jeck termed Natural Probabilities.

   He also used the data to make the remarkable proposal of replacing the figures in Appendix C with distance and probability based ones. While this has not yet been adopted, some of his proposals have been adopted as supplements.

   Natural LWC Probabilities

   Dr. Jeck introduces the term "Natural LWC Probabilities" in the context of discussing analysis of flight test data in DOT/FAA/AR-00/30 ¹:

   3.2 COMPARING WITH NATURAL LWC PROBABILITIES.

   One comparison that is not possible with Appendix C is the question of how common, or uncommon, was a particular test flight icing encounter? Or, how representative of nature is a particular icing wind tunnel exposure or computer …

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5. Origins of The Supercooled Cloud Database

   "Thanks are also due ... for their patience and support on this long project." ¹

   
   Public Domain image from DOT/FAA/AR-07/4.

   Introduction

   There are 28000 nmi of measured natural icing flight test data in the database, with over 6000 individual measurements. Data from more than two dozen organizations for flights between 1946 and 1988 (42 years) were collected into the database.

   Dr. Richard Jeck of the FAA was the lead in assembling the database.

   Dr. Jeck used the term "Supercooled Cloud Database", so here we will abbreviate that to Database or SCDB.

   The database took at least 14 years to assemble.

   Early Motivations for the Database

   Nearly of the database (14,372 nmi out of 28,000) of the Database already existed before Dr. Jeck started: The inflight icing data from the NACA-era. That data was the basis of the current Appendix C icing environment definitions. See Conclusions of …

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6. Aircraft Icing Intensities

   "AN ENGINEERING-ENABLED (MEASURABLE! AND CALCULABLE!) ICING SEVERITY SCALE"

   Title from an outline of topics by Dr. Jeck.

   
   Image from an Icing Information Note.

   Introduction

   Dr. Jeck's "A History and Interpretation of Aircraft Icing Intensity Definitions and FAA Rules for Operating in Icing Conditions" ¹ outlines the history in the US Code of Federal Regulations. Changes require a public comment period, so there was often debate (and on some occasions controversy). The definitions can affect which aircraft are certified perform Flight In Known Icing (FIKI), so there is great economic and practical interest to any changes.

   See 1969 Aircraft Ice Protection Report of Symposium for Dr. Jeck's summary of one controversial occasion in 1969.

   Dr. Jeck proposed a "universal curve" and made recommendations for changes as part of the The FAA Inflight Aircraft Icing Plan (discussed in "Dr. Jeck's Works on Supercooled Large Drops").

   FAA Inflight Aircraft Icing Plan ² Task …

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7. "New Replacement Figures for 14 CFR-25, 29, Appendix C"

   "Modernized Appendix C - The Beauty & Benefits of Digitized Figures"

   Quote from an unpublished outline of topics by Richard Jeck.

   

   Summary

   The late Dr. Richard Jeck of the FAA ¹ in his Icing Information Notes advocated "New Replacement Figures for 14 CFR-25,29, Appendix C".

   The "Icing Information Note" was essentially a draft of what became Appendix F of DOT/FAA/AR-07/4 ².

   Here, I will note a missed opportunity to make them available, and offer other "modernized" means of producing figures as an alternative.

   Appendix F

   As it is brief, Appendix F is reproduced in large part below:

   APPENDIX F—COMPUTERIZED VERSIONS OF 14 CFR PARTS 25 AND 29 APPENDIX C

   Title 14 Code of Federal Regulations (CFR) Parts 25 and 29 Appendix C (herein referred to as Appendix C) contains six graphs of design variables that are used by designers of in-flight ice protection systems and by data …

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8. "Icing Information Notes"

   "A Treasure Trove"

   

   Although horizontal extent is a common term in the icing literature, it has not been defined anywhere. Therefore, it is defined here in a way that is compatible with conventional usage.

   Public Domain figure and text from DOT/FAA/AR-07/4 ¹, also contained in a prior Icing Information Note.

   Summary

   Perhaps the best summary of Dr. Jeck's works is a summary that he wrote himself.

   In 2018 Dr. Richard Jeck, retired from the FAA, sent via private email a collection of his "Icing Information Notes" ["Notes"], which one reader dubbed "A Treasure Trove".

   I believe that this is one of the last communications on the technical topic that Dr. Jeck had, and the Notes may summarize what he viewed as some of the most important and useful of his decades of works.

   History of the Notes

   A biography ² explains:

   After Dr. Jeck transferred from NRL …

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9. 28,000 Miles of Data: The Publications of Dr. Richard Jeck

   "a number of advantages and uses of this new, distance-based format"

   
   Public Domain figure from DOT/FAA/AR-00/30.

   Dr. Richard Jeck ¹, retired from the FAA, passed away in January 2026 ².

   Dr. Jeck had over 60 publications in the area of aircraft icing ³. Many of them have been cited numerous times, and are currently cited in 2026.

   I knew Dr. Jeck professionally through industry organizations (AIAA, SAE) and meetings with the FAA.

   I had the opportunity to have a drink with him one evening circa 1993 at an AIAA meeting. He was generous with his time to a junior engineer.

   He was uniquely gifted in translating meteorological data into terms that could be understood and used by the diverse communities within aircraft icing (meteorologists, researchers, regulators, industry, pilots, academia, and others).

   Here we will review and celebrate some of his numerous technical publications.

   His obituary notes him …

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10. Seeking "Icing Information Notes"

    

    Although horizontal extent is a common term in the icing literature, it has not been defined anywhere. Therefore, it is defined here in a way that is compatible with conventional usage.

    Public Domain figure and text from DOT/FAA/AR-07/4, which are similar to one of the Notes. ¹

    Summary

    Dr. Richard Jeck, retired from the FAA, passed away in January 2026. ²

    I am putting together a series on Dr. Jeck's works (He had over 60 technical publications, so this may take a while).

    Circa 1997, Jeck started circulating "Icing Information Notes" ["Notes"] ³:

    "in response to requests from the field or to clarify known areas of confusion in the interpretation and application of icing data and technical literature."

    They were available on request.

    He apparently wrote them until 2012, and there appear to have been over 30 in total.

    I am seeking if anyone asked for and …

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11. Estimating Icing Conditions with Highest Drag

    "These data will be useful in evaluating and formulating ice accretion analyses and also performance penalty predictions."

    from NASA-TM-83556.

    

    Summary

    In "Ice Shape Drag Correlations" a correlation of drag due to icing was detailed using data from NASA-TM-83556 ¹. Here, we use the correlation to predict or estimate which icing conditions can result in the highest drag.

    The icing conditions predicted to have the highest Cd values cluster in a limited range of Figures 1 and 2 of Appendix C ², even when wide ranges of airspeed and altitude are considered.

    The Appendix C, Figure 1 Icing Environment

    We will use the Appendix C Continuous Maximum Icing Conditions.

    Appendix C Figure 1 defines LWC as a function of water drop size MVD (noted as "Median Effective Drop Diameter").

    
    Public Domain image.

    There is a standard horizontal extent of 17.4 nmi. defined that will be used here.

    A true airspeed …

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