Operators with approved de/anti-icing programs train both air and ground crews in factors including:

• Proper storage and handling (heating, dilution)
• Proper application (uniform thickness, no spray zones, nozzle settings)
• Proper HOT usage (communicate fluid type and strength, identify precipitation type & intensity, communicate start time, factors reducing HOT)
• Post fluid application check (who, how)
• Pre-takeoff check and pre-takeoff contamination check (who, how)

Transport Canada Statement Concerning Holdover Time Guidelines

In Canada, during active winter weather conditions, for an aircraft certified for flight in icing conditions, you must comply with CAR's 602.11/622.11 and have your critical surfaces free of frozen contamination prior to takeoff. Some private and commercial operators and all airline operators have Approved Ground Icing Programs (AGIP). These programs contain elements such as: the Operator's Management Plan; aircraft de-icing/anti-icing procedures; holdover timetables; aircraft inspection and reporting procedures; and training and testing.

Without an Approved Ground Icing Program, which means training on the use of Holdover Times (HOT) has not been conducted, the pilot would be unable to determine when potential fluid failure would occur and thus would not be able to gain maximum benefit from the HOT. In these cases, an external, tactile, pre-takeoff contamination inspection must be conducted immediately prior to takeoff, which is 5 minutes prior to the takeoff roll.

The use of holdover timetables (HOT) is not mandatory and may be used either as guidelines or decision-making criteria in assessing whether it is safe to take off. When holdover timetables are used as decision-making criteria, only high confidence level times shall be used and the procedures to be followed after holdover time has expired must be clearly documented in the operators plan.

Business Aircraft Operators can get additional information from the Canadian Business Aircraft Association (CBAA) regarding icing programs for their aircraft.

Be sure to check for the current version.

• Holdover Time Tables
• CARS (see 602 & 622.11)
• TP 10643, "When in Doubt... Small and Large Aircraft: Aircraft Critical Surface Contamination Training For Aircrew and Groundcrew"

Federal Aviation Administration Statement Concerning Holdover Time Guidelines

In the United States, only operators with a FAA approved program as described in FAR 121.629(c) are allowed to use holdover times in any manner other than advisory. This applies to Part 121, 125, and 135 operators.

For aircraft operating under Part 91, which includes private aircraft, there is no regulatory sanction for the use of holdover times.

Operators flying under FAR 121 must have an FAA approved winter operations program to operate in ground icing conditions. The program must include the use of holdover tables, training for pilots and ground crews, and a management plan detailing responsibilities for implementing the program. Alternately, Part 121 operators not wishing to develop a program must conduct an external check to ascertain the aircraft surfaces are free of any adhering frozen contamination and must take off within five minutes of conducting the check (FAR 121.629(d)).

FAR 125 and 135 Operators, after prescribed training, can use the holdover times in an advisory capacity, subject to an FAA approved check of adhering frozen contamination for each specific aircraft type to be accomplished within five minutes prior to takeoff. Additional resources are listed below.

• FAA Regulations
• FAA Air Transportation Division
• FAR 91.527, "Operating in Icing Conditions"
• FAR 135.227, "Icing Conditions: Operating limitations"
• FAR 121.629 "Operation in icing conditions"
• AC 120-58, "Pilot Guide Large Aircraft Ground Deicing"
• AC 135-17, "Pilot Guide Small Aircraft Ground Deicing"
• FAA Airline Safety
• AC 135-16, "Ground Deicing and Anti-icing Training and Checking"
• AC 120-60B, "Ground Deicing and Anti-icing Program"
• AC 20-117, "Hazards Following Ground Deicing and Ground Operations in Conditions Conducive to Aircraft Icing"

Civil Aviation Authority Statement Concerning Holdover Time Guidelines

In the United Kingdom, during winter weather conditions, the following guidance applies if your aircraft is certified for flight in icing conditions. You must comply with Article 52 of the Air Navigation Order (Pre-flight action by commander of aircraft), JAR OPS 1.345 (Ice and other contaminants – ground procedures), 1.346 (Ice and other contaminants – flight procedures) and other relevant regulation, including information contained in the Aircraft Flight Manual.

Hold Over Time (HOT) Guidelines are generally used by Air Operator Certificate (AOC) holders as part of company winter operations procedures and as such fall within the remit of CAA regulatory oversight. Significant training is required before HOT guidelines can be used and therefore they should only be used by competent personnel.

Additional Resources:

• CAA
• CAA - JAR Ops 1.345(b):
• AEA "Recommendations for De-Icing / Anti-Icing of Aircraft on the Ground"
• List of General Aviation Publications
• CAA Winter Operations

Outside Air Temperature

Although the freezing point of anti-icing fluid is lower than that of pure water, it can freeze. As the air temperature drops, anti-icing fluids become less able to absorb and melt the freezing precipitation.

In addition, as the temperature decreases, the fluids become more resistant to shearing off the aircraft during the take-off roll.

It can get so cold that a fluid cannot be used safely on an aircraft either because it cannot afford any protection or because it may substantially interfere with the airflow over the lifting surfaces. A Lowest Operational Use Temperature (LOUT) is specified for every fluid. When the temperature is below the LOUT, that fluid should not be used. (See Module 3: Fluid Basics for more information on LOUT.)

Precipitation Type and Intensity

Anti-icing fluids work by absorbing and melting precipitation. Conversely, precipitation dilutes the anti-icing fluid. The more dilute the anti-icing fluid becomes, the less protection it affords. Ultimately, the anti-icing fluid will fail. The more moisture present, the shorter the holdover time.

Both the type of precipitation and its intensity are key factors in determining HOT.

Fluid Type and Concentration

Type I must always be applied heated and diluted. It is essentially a de-icing fluid that can also be used for anti-icing in a two-step process. As the least viscous (thinnest) of fluids, it has the shortest HOTs.

Types II, III and IV may be applied unheated or heated, full strength or diluted. The thickening agents added to these fluids to increase viscosity, and correspond to longer HOTs. In general, the more dilute the Type II, III or IV fluid, the shorter the holdover time. Check to see if thickened fluids can be used on your aircraft, and if any changes to the takeoff procedure (e.g., delayed rotation speed) are required.

See Module III: Fluid Basics for a more comprehensive discussion.