getting to grips with COLD WEATHER OPERATIONS 寒冷天气运行(42)

Effective: October 1, 1999

● General Notes
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ACTIVE FROST means that the weather conditions are such that frost is actually forming. This is in contrast to the situation where frost has formed on the airplane, but frost no longer forms at the time of de-icing. In that case, no protection for frost re-formation needed if the frost was still actively forming is needed after the de-icing.

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The Flight Standard Information Bulletin for Transportation (FSAT 99-07) effective date 01 October 1999 publishes the FAA-approved de-icing program updates for winter 1999-2000. It includes revised SAE-approved holdover time guideline charts (reproduced here above). On all these charts a new column has been added with a heading of .Others (1).. This new column, with its supporting note, delineates the fact that no holdover time guidelines exist for the conditions of snow pellets, snow grains, ice pellets, moderate and heavy freezing rain and hail. FSAT 99-07 also mentions that, as such, air carriers should not attempt takeoff in conditions of snow pellets, snow grains, ice pellets or hail unless operations in these conditions are approved by the aircraft manufacturer and a pre-takeoff contamination check is performed. Takeoffs in conditions of moderate and heavy freezing rain are not approved. Airbus Industrie does not approve takeoff in any of the above-mentioned conditions (i.e. snow pellets, snow grains, ice pellets or hail). Indeed, the requirement is to comply with the clean aircraft concept; i.e. no precipitation accumulation is permitted on the aircraft during takeoff. Therefore, as long as no holdover times exist for conditions of snow pellets, snow grains, ice pellets or hail, takeoff in these conditions is not recommended.

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FSAT 99-07 also publishes additional FAA-approved manufacturer specific Type II and Type IV de-icing / anti-icing holdover time tables.

Table 4
Guidelines for the application of SAE Type I fluid mixtures.

Minimum concentrations as a function of Outside Air Temperature (OAT)
Outside Air Temperature OAT  One-step Procedure De-icing/anti-icing  Two-step Procedure 
First step: De-icing  Second step Anti-icing (*) 
-3° C (27° F) and above  Freezing point of heated fluid (**) mixture shall be at least 10° C (18° F) below OAT  Water heated to 60° C (140° F) minimum at the  nozzle or a heated mix of fluid and water  Freezing point of fluid mixture shall be at least 10° C (18° F) below actual OAT 
Below -3° C (27° F)  Freezing point of heated fluid mixture shall not be more than 3° C (5° F) above OAT 
Note: For heated fluids, a fluid temperature not less than 60° C (140° F) at the nozzle is desirable. Upper temperature limit shall not exceed 90°C or fluid manufacturers recommendations. Caution: Wing skin temperatures may differ and in some cases may be lower than OAT. A stronger mix (more Glycol) can be used under the latter conditions. 
　
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