Automated Hold-Over Time (HOT)

HOT tables are the worldwide industry standard for guidance on deice and anti-icing fluid efficency.

Whether incorporated into your approved 121 or 135 deicing program or as a reference for operating part 91, the HOT module is an indespensible tool for calculating correct hold-over times while adhering to all the restrictions and limitations attached to the printed tables as footnotes.

Current regulations under FAR Parts 121 and 135 rely on the "clean aircraft" concept; meaning that no person may takeoff an airplane when frost, ice, or snow is adhering to the wings, control surfaces, or propellers of the airplane (FAR Sections 121.629 and 135.227). The rationale behind this concept is that the presence of even minute amounts of frost, ice, or snow on particular airplane surfaces can cause a potentially dangerous degradation of airplane performance and unexpected changes in airplane flight characteristics.

Under current regulations, ultimate responsibility for determining whether the airplane is free of contamination  rests with the pilot in command (PIC).

Both the FAA and industry have developed guidance and recommended procedures that are designed to help the PIC in making that determination. These procedures include monitoring weather conditions and temperature changes, visual checks, and using deicing/anti-icing fluids.

Deicing/anit-icing fluids only remain effective (i.e prevent the formation of frost, ice or the accumulation of snow on the aircraft surface) for a limited time.  That time range can change dramatically based on temperature, precipitation intensity, winds and fluid type. Hold-over times even vary significantly from one brand to the next.  In other words, not all type II or IV solutions are the same.  Footnote restrictions exist for all solution types.  The combination of these factors can lead to erroneous conclusions regarding the protection afforded by the solution.

When conditions conducive to the formation of frost, ice, or snow on airplane surfaces exist at the time of takeoff, those surfaces should be checked for contamination in accordance with FAR Section 135.227.

Current Data

Each year HOT tables are developed by solution manufacturers, inaccordance with SAE and ISO standards, annually.  These tables are then published by the regulatory agencies around July and August of each year. The differences from year to year may be minor or substantial.  European (AEA) publications do not provide individual brand data, only SAE Type I-IV solutions. US and Canada provide both SAE I-IV and individual brand time ranges.

The HOT module displays a screen indicating the currency of the data.

Simple to Use

The module steps the user through the process.

Only information that is pertenent to the type of precipitation is presented.

Notice, to the right, that Active Frost only requires a temperature input; while other types of precipitation require more information.  In this case, Ice Pellets require the user to verify if the precipitation is mixed with other forms of precipitation and the intensity.

Snow Visibility

Recently, regulatory agencies have mandated the use of prevailing visibility to determine precipitation of snow intensity.  This calulator is integrated into the HOT module.  As with the regulation, the calculated intensity can be overriden by acknowledging fog or haze have diminished the visibility.

Selecting a Time

 The HOT tables provide ranges of time limits.  These limits are agumented by several factors, listed in the footnotes of the publications.  The factors adversely effect the duration of efficiency of the fuild uniquely and they are cumulative in effect.  The PIC is left to determine the best hold-over time.  Not to worry. The module displays the relative affect of the factors on a color scale.  The pilot can use the slider to determine the best time margin for his unique conditions.

Starting the Clock

Hold-over times are valid from the beginning of the anti-icing solution application.  In a two step process, deicing followed by anti-icing, the user waits until the deicing is completed then starts the clock when the anti-icing solution is first applied.  The user can manually enter the time or click the start button.  The time begins the count-down to zero.

The user can leave the screen and do other tasks within EFB-Pro.  The HOT button will illuminate GREEN as long as there is time left on the clock. When the clock reaches zero, the button and the timer turn RED.

Even if the pilot does not intend to use the count-down clock, the hold-over time calculation is invaluable.

Allowance Time vs Hold-over Time

Since ice pellets typically remain in the frozen state within type IV solution, hold-over times are not provided for ice pellet precipitation. However, when using type IV fuilds, the tables do provide an allowance time under certain conditions.  This time frame calculates the window, when either takeoff must occur or active preciptation of ice pellets must cease, not restart and the temperature must not decrease, for the solution to "carry" the ice pellets off when the type IV solution is shed during acceleration. 

If conditions are met, the type IV solution can be considered effective as long as 90 minutes.  This conditional end-time is calclated for the pilot.

EFB Brands that endorse EFB-Pro

CMC PilotView

System Requirements