Aircraft Icing

Bookmark and Share

FAA’s Updated Deicing Procedures Include Holdover Time Changes

December 14, 2012

Aircraft operators preparing for winter operations and possible airport deicing are encouraged to review the 2012-2013 Federal Aviation Administration (FAA) Holdover Tables outlining aircraft deicing procedures. The revised document includes changes that, while small, could alter operator procedures based upon last year's deicing holdover times.

"We recommend operators familiarize themselves with the new information for the current winter season, and identify any changes to guidelines for the deicing materials they use," noted Doug Carr, NBAA vice president of safety, security, operations & regulation. "This information changes every year, as material is harvested and tested, and fluid chemistry changes."

Deicing formulas are categorized from Type I through Type IV, depending on fluid composition and application procedure. Low-viscosity Type I deicing fluids flow quickly from aircraft surfaces, making them ideal for light applications and composite surfaces, while the remaining three fluid types are considered "anti-icing" fluids and contain thickening agents to provide increased protection from ice adhesion to aluminum and other metal surfaces.

Type II and Type IV fluids are often used on commercial airliners, large business aircraft and for applications during heavy snowfall. Type III - a compromise of sorts between Types I deicing and Type II anti-icing fluids - is used for metal-skinned aircraft with a rotation speed of less than 100 knots.

The revised guidance includes changes to rated holdover times (HOT), or the length of time an aircraft may wait to depart following application of an approved deicing fluid. HOT values depend on fluid type, manufacturer and application.

For example, recent FAA tests of Type I fluid flow rates on composite surfaces has resulted in shorter holdover time values for composite-bodied aircraft, relative to comparable metal-skinned aircraft. Several HOT tables have also been revised slightly to reflect the deletion of obsolete fluid types.

Lowest Operational Use Temperature information for all fluids has also been updated for some applications due to revised information from some fluid manufacturers. Changes have also been made to the Active Frost Holdover Times and Snow Visibility tables, with minor wording revisions to Fluid Application Procedures and Ice Pellet Allowance Times.

"Knowledge of even the most subtle changes in holdover time effectiveness are important to Members who might face extended ground delays prior to takeoff," Carr said.

Operators may review the revised guidelines here.