FAA 2009-2010 HOT Changes

Page history last edited by Neil Singer 3 mos ago

In previous years, the FAA Snow Intensity Table was only required for Type I HOTs, and recommened for Type II, III, and IV. Recent analysis of test data indicates that the FAA SIT is far more accurate in estimating snowfall intensity than the method used by weather observers and ASOS. Thus, use of the FAA SIT is now required for determining HOTs in snowfall for all fluid types.
1. If visibility is reduced due to non-snow obscurations (fog, etc.), the FAA SIT need not be used, as it will needlessly overestimate the actual snowfall intensity.
Active Frost HOT have been moved to a new frost only table.
1. Research indicating failure of Type II and IV during active frost at low temperatures led to reducing times for these fluids.
2. Type II, III, and IV have an application limit of -25C due to radiational cooling of aircraft surfaces to temperatures colder than OAT in active frost conditions.
Type II and IV HOT tables have had the "Below -25C" row removed; tables are now only approved to -25C.
1. If manufacturer publishes lower operational use temperature (LOUT), the "-14C to -25C" row may be used down to the LOUT.
Removal of one approved Type II fluid caused three generic Type II cells to increase published HOTs.
Addition of new approved Type IV fluid caused one generic Type IV cell to reduce published HOT.
Note added that in conditions of light snow mixed with light rain, the light freezing rain HOTs can be used.

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