Purpose:

The purpose of this SAE Aerospace Standard (AS) is to provide guidelines for the components and configurations that define the four versions of the Weather Support to Deicing Decision Making (WSDDM) winter weather nowcasting system.

Motivation:

Deicing/anti-icing endurance time data presented to the SAE G-12 Holdover Time Subcommittee by testing laboratories for examination and validation have clearly shown that the liquid equivalent snowfall rate is the most important factor in determining the endurance time of a deicing/anti-icing fluid. However, current National Weather Surface stations do not provide liquid equivalent snowfall rates, but rather hourly snow intensity estimates based on visibility. Snow intensity estimates based on visibility have been shown to be misleading when wet snow, heavily rimed snow (snow that has accreted significant amounts of cloud droplets), and snow containing single crystals of compact shape (nearly spherical) occur. Under these conditions, visibility can be judged to be high due to the relatively small size (cross sectional area) of these types of crystals, leading to estimates of light snowfall intensity when in fact the actual snowfall rate in liquid equivalent terms is moderate to heavy. Researchers define the hazard as high-visibility, high-snowfall rate conditions. Researchers examined five of the major ground deicing accidents and showed that high-visibility, high-snowfall rate conditions were present during many of these accidents. All of the accidents had nearly the same liquid equivalent rate of 2.5 mm/hour (0.1 inch/hour), but widely varying visibilities. The WSDDM system was designed to directly address this concern by including snowgauges that measure snowfall rate every minute as one of the systems core components.

A second motivation in the design of the WSDDM System was to provide airlines and airport authorities with real-time accurate weather information that can be used to improve decision making regarding aircraft ground deicing/anti-icing operations and airfield snow crew management.

Units:

The values stated in SI units are to be regarded as the standard.

Safety:

While the materials, methods, applications, and processes described or referenced in this document may involve the use of hazardous materials, this document does not address the hazards that may be involved in such use. It is the sole responsibility of the user to ensure familiarity with the safe and proper use of any hazardous materials and processes and to take necessary precautionary measures to ensure the health and safety of all personnel involved.