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Icing: Winter is Coming

Meteorology | October 6, 2015

Author: Brent Fishlock


As the winter flying season approaches in many parts of the world, we are reminded by cool temperatures and morning frost that we must be vigilant in our critical surface inspections. Accidents with fatal consequences where crews either didn’t notice or chose to ignore the warning signs of contamination on aircraft surfaces have happened all too recently. The time spent de-icing or planning to hangar an aircraft where possible far outweigh the risks of doing neither.

Aircraft icing and the science of de-icing is a dynamic subject that should not be considered mastered at any point in a person’s career. Regulators annually review de-icing documentation after performing trials on new fluids and technologies. The Federal Aviation Administration (FAA) and Transport Canada (TC) jointly support the testing of anti-icing fluids, and with the assistance of the SAE Holdover Time Subcommittee, they evaluate the test results and publish the recommended HOT guidelines for the manufacturer-specific fluids. The Association of European Airlines publishes similar HOT guidelines and recommendations for de-icing/anti-icing of aircraft on the ground.

When studying the FAA/TC document, be sure to review the Summary of Changes and Key Guidance for Winter sections for any new procedures. Some notable changes and key guidance reminders for 2015/2016 include the following:

  • The use of RVR is not permitted for determining visibility used with the holdover tables.
  • Research has determined that fluid degradation is accelerated by the steeper angles of the flaps/slats in the takeoff configuration. The degree of potential degradation is significantly affected by the specific aircraft design. The 90% adjusted tables provide holdover/allowance times that must be used when flaps and slats are deployed prior to de/anti-icing. Standard holdover/allowance times can be used if flaps and slats are deployed as close to departure as safety allows.
  • The “Winter 2015-2016” document has been updated to provide proper guidance for determining which holdover times/allowance times should be used with METAR code GS. The World Meteorological Organization (WMO) states that METAR code GS is used for two meteorological conditions: “snow pellets” and “small hail.” However, this is not the case in Canada. Caution needs to be exercised when determining holdover times when METAR code GS is present. Always refer to your regulatory documents.
  • Significant changes, primarily increases, have been made to the Type IV generic holdover times as a result of the new and removed Type IV fluids.
  • A new note has been added to the allowance time tables to indicate that if an intensity is reported with small hail, the equivalent ice pellet condition can be used (i.e., If light small hail is reported, the light ice pellet allowance times can be used. If an intensity is not reported, the moderate ice pellet allowance times must be used.).

Always review the latest guidelines provided by your regulator and your training provider.

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