This is a funny looking Holdover Time Table
- Dan Boedigheimer
Holdover times and Regression information
When you go to the Aircraft Ground Deicing page on the FAA web site to retrieve Holdover Time Tables this year you will see another document is available: 2013-2014 Regression Information. This is the first year the FAA has published this document, although a similar document has been in use by Transport Canada since 2009.
The short story is you can ignore this document. It is designed for Holdover Time Determination System (HOTDS) manufactures only. If you want to learn more about what HOTDS is, continue reading.
Every year, the FAA and Transport Canada assess the Holdover Time (HOT) performance of fluids. The tests are conducted under controlled conditions of precipitation type, precipitation rate, and temperature. The quantity of precipitation, also known as liquid water equivalent (LWE), is measured in units of grams/decimeter squared/hour.
To accurately calculate HOTs, pilot’s needs accurate, real-world information on temperature, precipitation type and rate. The precipitation rate reported in METARs (as light, moderate, or heavy) is not correlated with LWE used during fluid testing. The result is that the pilots must make a subjective assessment.
Companies like DAN-ICE have developed meteorological and support equipment for use with HOTs. The goal is a simple way flight crews can obtain more accurate HOTs. The HOTDS system can also be thought of as an automated electronic version of the HOT Guidelines that includes software algorithms to refine the HOT based on liquid water equivalent systems (LWES) that measure precipitation rate in real-time. To use HOTDS you need to be at an airport that measures LWES and you would need to subscribe to a company like DAN-ICE that provides the refined HOT via ACARS.
The 2013-2014 Regression Information document includes the regression coefficients and equations which companies like DAN-ICE use as the software algorithms to provide a more accurate holdover time.
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