Chapter 11 - Holdover Time Guidelines and Associated Procedures

11.1 Holdover Time (HOT)

11.1.1 Holdover Time Guidelines - General

Holdover Time tables are referred to as Holdover Time Guidelines because this term more appropriately represents their function in providing guidance to flight crew and the need for the flight crew to use judgment in their interpretation.

Holdover time guidelines provide an estimate of the length of time anti-icing fluids will be effective. Because holdover time is influenced by a number of factors, established times may be adjusted by the pilot-in-command according to the weather or other conditions. Air Operators' manuals must describe the procedures to be followed for using holdover time guidelines. When the guidelines are used as decision-making criteria, the procedures to be followed by the pilot-in-command for varying the established values must also be specified.

The estimated time is expressed as a range in the Guidelines and is based upon the type and concentration of the specific fluid, the outside air temperature, and the kind and intensity of precipitation involved. Individual holdover timetable cell values are capped at 2 hours for all precipitation conditions except freezing fog, which is capped at 4hours.

The HOT guidelines are applicable to an aircraft experiencing ground icing conditions and do not apply once the aircraft is airborne.

The time that the fluid remains effective is the time from first application of anti-icing fluid on a clean wing until such time as ice crystals form or remain in the fluid creating a surface roughness. Holdover time cannot be precisely determined because it depends on many variables. Some of the variables include: prevailing precipitation type, intensity, temperature, wind and the humidity. The aircraft type and its configuration, effectiveness of the treatment on surfaces, taxiing direction relative to the wind and jet blast from other aircraft are equally important. The effects of these variables need to be taken into account by the Pilot-in-Command when establishing the HOT value. There is no simple solution to this complex issue.

Transport Canada has, for a number of years, published Holdover Time Guidelines that were the same as those published by the Society of Automotive Engineers (SAE) for generic fluids and were based upon the recommendations of the SAE G-12 Holdover Time Subcommittee. The SAE has chosen to cease publishing generic HOT Guidelines, as of 2002.

The Federal Aviation Administration (FAA) and Transport Canada (TC) jointly support the testing of anti-icing fluids, on a cost recovery basis, and, with the assistance of the members of the SAE Holdover Time Subcommittee, evaluate the test results and publish the recommended HOT guidelines for the manufacturer specific fluids. The generic table for Type II and IV fluids are based on these manufacturers' tables and are also published by Transport Canada and the FAA. This procedure will continue with both the FAA and Transport Canada publishing the HOT Guidelines.

11.1.2 Current HOT Guidelines

Current HOT Guidelines can be found at the following website: http://www.tc.gc.ca/

The following information can be found at the above website:

  1. Type I deicing fluid generic HOT Guidelines;
  2. Type II anti-icing fluid HOT Guidelines;
  3. Type III anti-icing fluid HOT Guidelines;
  4. Type IV anti-icing fluid HOT Guidelines;
  5. Currently Qualified Fluids Listing;
  6. SAE Type I Deicing Fluid Application Procedures;
  7. SAE Types II, III & IV Anti-Icing Fluid Application procedures;
  8. Visibility in snow vs. snowfall intensity chart; and
  9. Minimum 'on wing' viscosity table.

11.1.3 Use of Holdover Time as a Decision Making Criterion

GOFR622.11 states in part: "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".

11.1.4 Establishing the HOT range

Establishing the appropriate HOT time range will require the acquisition of at least the following information:

  1. Choose the precipitation type;
  2. Determine the precipitation rate;
  3. Note the fluid in use, including:
    1. Fluid Type; and
    2. Fluid manufacturer.

  4. The fluid dilution must be determined; and
  5. OAT must be noted.

Using this information, enter the appropriate HOT guideline and identify the HOT cell containing the range of times available.

11.1.4.1 ESTIMATING THE PRECIPITATION RATE

  1. Snowfall rate


    The meteorological approach to estimating snow rate has always been based on visibility alone. Scientific research has indicated that the use of visibility in snow as the sole criteria for establishing snowfall rate/intensity is invalid. The evidence indicates that a visibility and temperature pair needs to be used for establishing more accurate snowfall rates. The highest snowfall rates occur near 0°C.

    It has also been determined that during night snowfall conditions for the same snowfall rate, visibility is about twice as good as it is during the day. This factor must also be considered in estimating the snowfall rate.

    The relationship between visibility and snowfall intensity is analyzed and documented in TP14151E. The relevant information from this TP document is contained in the 2003 Transport Canada visibility in snow vs. snowfall rates chart.

    Example: based upon the 2004 Transport Canada visibility in snow vs. snowfall intensity chart, assume that the daytime visibility in snowfall is 1 statute mile and that the temperature is -7°C. Using the "visibility in snow vs. snowfall intensity chart", we conclude that the snowfall rate is light. This snowfall rate will be used to determine which HOT Guideline value is appropriate for the fluid in use.

    NOTE: The Transport Canada 'visibility in snow vs. snowfall intensity' chart can be found along with the current HOT Guidelines through the Transport Canada website: http://www.tc.gc.ca/.
  2. Precipitation rates for other than snow.

    Meteorological reports of precipitation rates for the airport of operation may be the best source of information for forms of precipitation other than snow.


    Meteorologists report light freezing drizzle (-ZR) for a wide range of precipitation rates. Canadian meteorologists report light freezing drizzle for precipitation rates ranging from trace to 1.2 mm/hr.

    The pilot alone has no way to measure or otherwise reasonably judge what the freezing drizzle precipitation rate is other than to receive information about the measurements taken by qualified meteorological persons. This measurement report will imply a rather wide range of possible precipitation rates. The worst case rate must be assumed. That is, the highest precipitation rate must therefore be assumed, and hence the lowest HOT value in freezing drizzle cell, for the conditions, should be chosen.

    Likewise for light freezing rain the meteorologist reports would imply a rather wide range of precipitation values for the condition from 1.2 to 2.5 mm/hr. Again the lowest time value in the HOT cell for the conditions, corresponding to the highest rate, should be chosen.

11.1.4.2 DETERMINING THE LOWEST TIME VALUE FOR THE PRECIPITATION CONDITIONS PRESENT

Once the appropriate cell within the HOT Guidelines table for the conditions, temperature and fluid in use has been established, the lowest time value, based upon the precipitation rate, needs to be established. The process for obtaining this value may best be illustrated by use of an example.

Snow Example:

Assume that the precipitation condition is moderate snow. The fluid in use is a TypeIV fluid and the generic TypeIV HOT table will be used. The concentration of the fluid is 100/0. The temperature range is 00C to -30C. Using this information it has been determined, by locating the correct cell, that the range of HOT times for these circumstances is 0:30 - 0:55, i.e. thirty minutes to fifty-five minutes.

For this example, the lowest HOT time limit is 0:30 minutes, based upon the published HOT guidelines for 2004/2005, accessible through the Transport Canada website.

Discussion:

The time limit is 0:30 minutes because the times shown in the HOT guideline cell, i.e. 0:30 - 0:55, are the range of values from moderate to light snow.

If the precipitation condition were light snow, then the upper limits, i.e. maximum time value, would be fifty-five minutes (0:55).

11.1.5 Elapsed time is less than the lowest time in the HOT cell

Transport Canada has previously considered that, under an approved ground icing program, if the lowest time in a cell has NOT been exceeded for conditions covered by the Guidelines, there is no requirement to inspect the aircrafts' critical surfaces prior to commencing a take off.

This position was based on evidence gained during fluids testing. The HOT values are very conservative for the lowest number in the cell, if the conditions present are NOT in excess of those conditions represented by the table, e.g. for snow it would be a moderate snow condition.

In light of the fact that there could be significant variability in assessing weather conditions, Transport Canada no longer considers it prudent or reasonable to depart without a specific inspection. Therefore, take off under any circumstances without an appropriate approved inspection technique being employed prior to take off is no longer considered acceptable.

11.1.6 Elapsed time within the range of HOT for the conditions

Transport Canada considers that when the time that has expired since anti-icing is within the range of time chosen by the Pilot-in-Command for the conditions present and covered by the Guidelines, there is a requirement to conduct an inspection prior to takeoff. This inspection will usually be conducted from within the aircraft and may be an inspection of one or more of the representative surfaces of the aircraft. The inspection must be described in the Air Operators Approved Ground Icing Program.

11.1.7 Holdover Time Exceeded

11.1.7.1 Section6.3 of the General Operating and Flight Rules 622.11 states, in part: "When holdover time tables are used as decision making criteria, take-off after holdover times have been exceeded can occur only if a pre-take-off contamination Inspection is conducted, or the aircraft is de-iced/anti-iced again".

11.1.7.2 Transport Canada's interpretation of the phrase "inspected immediately prior to take-off", in the ground icing context, is that the inspection must be conducted within five minutes prior to beginning the take-off roll, except for TypeI fluids.

11.1.7.3 Fluid testing has indicated that the above procedure must not be applied to TypeI fluids. Type I fluids have very short HOT performance and fluid failure occurs suddenly. Therefore, it is not considered prudent to apply this procedure to TypeI fluids. The procedure must only be applied to TypesII, III and IV anti-icing fluids and then only when the pertinent minimum holdover time equals or exceeds 20 minutes.

11.1.7.4 If, after conducting the contamination inspection, it is not possible to take-off within five minutes, the aircraft must return for deicing/anti-icing.

11.1.7.5 Transport Canada considers that, when the time that has expired since anti-icing is greater than the largest value in the range of time chosen for the conditions present and covered by the Guidelines, there is a requirement to conduct an inspection of the critical surfaces prior to takeoff. This inspection must be conducted from outside the aircraft. This inspection must be described in the Air Operator's Approved Ground Icing Program.

11.1.7.6 Fluid testing experience and operational testimony indicates that the ability of the Pilot-in-Command or his delegate to effectively examine the critical surfaces from within the aircraft, when the HOT has expired and the fluid may have failed, to be doubtful. Further, long exposure to frozen precipitation, wind and other factors, may have resulted in fluid failure in areas NOT visible from the inside of the aircraft. This last point is crucial. This is a high risk scenario which due diligence indicates requires a very thorough action.

11.1.7.7 Once the HOT time clock has been started it must not be stopped for intermittent precipitation. Intermittent precipitation conditions, during ground icing operations, are a common occurrence at some airports. As precipitation falls on an aircraft that has been anti-iced, the fluid is being diluted. The more diluted the fluid becomes, the more readily it flows off the aircraft, and the higher the freezing point becomes. Even if the precipitation stops falling, the diluted fluid will continue to flow off the aircraft due to gravity. There is no practical way to determine how much residual anti-icing fluid is on the wing under these circumstances. HOT values under these conditions have not been assessed. Therefore, after the anti-icing HOT clock has been started, it must not be stopped. HOT credit cannot be given due to the fact that the precipitation has temporarily stopped falling.

11.1.8 Meteorological Conditions for which the HOT Guidelines are not applicable

The HOT Guidelines do not include guidelines for all meteorological conditions. The conditions not covered are generally expected to result in short times of protection; they include:

  1. Ice Pellets;
  2. Snow pellets;
  3. Hail;
  4. Freezing Rain;
  5. Ice Pellet Conditions; and
  6. Heavy Snow Conditions.

NOTES:

  1. Operations should be stopped when these conditions exist.
  2. Additionally, aircraft are NOT certified for flight in freezing rain conditions.

11.1.9 Use of approved fluids

Qualified fluids have undergone laboratory testing to meet performance specifications and to confirm their aerodynamic acceptability. They have also been subjected to endurance time tests from which the holdover guidelines have been developed. Material compatibility tests are also conducted to ensure that the deicing fluids do not damage aircraft exterior surfaces or components. The operator is ultimately responsible for ensuring that only qualified fluids are used when the HOT Guidelines are being utilized.

11.1.10 HOT Guidelines

Air Operators choosing to not use HOT Guidelines will be expected to accomplish a pre-takeoff contamination inspection, from outside the aircraft, in all cases. This inspection must be conducted from outside the aircraft. The Pilot-in-Command will not have an indication of impending fluid failure, as would be the case when using the HOT Guidelines. An outside the aircraft inspection will always be required to establish the condition of the fluid. Fluid failure must always be considered to be imminent or to have occurred in this case, to satisfy the intent of the Regulation.

11.1.11 Lowest Operational Use Temperature (LOUT)

See Chapter8 on Fluids for an explanation and an example of establishing a LOUT.

11.2 Deicing and Anti-icing Inspection

11.2.1 General

The deicing process is intended to remove frozen contaminants from the aircraft's critical surfaces and to restore the aircraft to a configuration that neither significantly degrades the aerodynamic performance characteristics and handling qualities nor causes mechanical interference to occur. The criteria used to make the decision on whether or not to de-ice an aircraft is an integral part of the Air Operators Approved Ground Icing Program.

Where required, the Air Operator's approved program must describe the methods to be used in this inspection, which may be conducted from the inside or the outside of the aircraft. The inspection may be visual or tactile, or may include the use of approved ground ice detection devices. The inspection may use representative aircraft surfaces to judge the extent of contamination. In some cases an outside the aircraft inspection is mandatory, for example, when an Air Operator with an approved program is not using HOT guidelines.

Where only a visual inspection is done, the Air Operator's Program must specify the conditions, such as weather, lighting and visibility of critical surfaces, under which such an inspection can be conducted. Unless other procedures have been specifically approved, a tactile external inspection must be conducted on all aircraft without leading edge devices, such as the DC9-10 and the F-28, and on any other aircraft as designated by the Director, Commercial and Business Aviation, Transport Canada.

There have been ground icing accidents associated with the improper inspection of high wing turboprop aircraft employed in commercial service. Particularly vulnerable are those high wing turbo prop aircraft operated from remote locations with minimal facilities. For these types of operations, the pilot is usually the final person to perform the pre-take-off inspection. It is often difficult to clearly see frozen contaminants from a brief view of the upper wing surface, especially if the pilot is balancing on a strut to gain the necessary view. The use of proper inspection equipment, such as wing inspection ladders, is highly recommended.

It is the pilot-in-command's responsibility to ensure that aircraft critical surfaces are not contaminated at take-off. When the pilot-in-command does not conduct the inspection, the delegated person must provide an inspection report in clear language to the pilot-in-command, who must indicate that the report is complete and understood. A detailed description of the guidelines and procedures to be followed in communications between the delegated and the pilot-in-command, including the use of hand signals, must be included in the appropriate Air Operator's manual.

11.2.2 Suggested Ground Icing Operational Practices.

The following practices help the Pilot-in-Command ensure that his aircraft is safe for take-off:

  1. Be aware of the adverse effects of surface roughness on aircraft performance, flying qualities and flight characteristics;
  2. Be knowledgeable of the ground de/anti-icing practices and procedures being used on the aircraft;
  3. Do not allow the service provider organization to de/anti-icing your aircraft until both parties are familiar with the ground deicing practices and quality control procedures to be used;
  4. Be knowledgeable of the critical surfaces of the aircraft and ensure that these areas are properly de/anti-iced;
  5. Ensure that precautions are taken during the deicing process to avoid damage to aircraft components and equipment;
  6. Ensure that a thorough post de/anti-icing inspection is performed prior to take-off;
  7. Perform additional post de/anti-icing inspections as required;
  8. Ensure that engines or rotor blades are not be started until it has been ascertained that all ice deposits have been removed and that ground personnel are away from the danger areas for such procedures. It should be noted that ice particles shed from rotating components may damage the aircraft or injure ground personnel;
  9. Be aware that operations in close proximity to other aircraft can cause snow, ice particles, or moisture to be blown onto critical aircraft components; or, can cause dry snow to melt and refreeze on aircraft critical surfaces;
  10. The aircraft must not take-off if snow or slush is observed splashing onto critical areas of the aircraft, wing leading edges, control surfaces, or high lift devices, during taxi; and
  11. The aircraft must not take-off if positive evidence of a clean aircraft cannot be established.

11.2.3 Critical Surface Inspection

11.2.3.1 INTRODUCTION

Current regulations call for a "clean aircraft" concept, which may be determined through pre-flight inspections using visual, tactile or sensor based procedures.

The "clean aircraft" concept is, in large part, assured by the Critical Surface Inspection, which is a pre-flight external inspection of critical surfaces conducted by a qualified person, to determine if the surfaces are contaminated by frost, ice, slush or snow. Under ground icing conditions, this inspection is mandatory.

The critical surface inspection phase is of prime importance in the overall deicing process and is directly related to the safety of the aircraft during take-off. Critical surface inspection procedures must therefore be design to ensure that an aircraft is free of contamination following deicing. During ground icing conditions with falling precipitation adhering to the critical surfaces, anti-icing will be required.

A Critical Surface Inspection is required by GOFR622.11, and it states that: "This inspection is mandatory whenever ground icing conditions exist, and if the aircraft is de/anti-iced, must take place immediately after final application of the fluid. After the inspection, an inspection report must be made to the pilot-in-command by a qualified person".

11.2.3.2 POST DE/ANTI-ICING APPLICATION INSPECTION

The following is a checklist of typical items to inspect, which may vary for different aircraft types. Recommendations from the aircraft manufacturer must be used when available.

  1. Wing leading & trailing edges, upper and lower surfaces;
  2. Leading edges, upper and lower surfaces, and side panels of vertical and horizontal stabilizing devices;
  3. High lift devices such as leading edge slats and leading or trailing edge flaps;
  4. Spoilers and speed brakes;
  5. All control surfaces and control balance bays;
  6. Propellers;
  7. Engine inlets, particle separators, and screens;
  8. Windshields and other windows necessary for visibility;
  9. Antennas;
  10. Fuselage, including emergency exits and windows used by the crew for examining critical surface contamination;
  11. Exposed instrumentation devices such as angle-of-attack vanes, pitot-static pressure probes, and static ports;
  12. Fuel tank and fuel cap vents;
  13. Cooling and auxiliary power unit (APU) air intakes, inlets, and exhausts; and
  14. Landing gear, including gear doors.

NOTE: Once the post de/anti-icing inspection has been completed and is satisfactory, the aircraft should be released for take-off as soon as possible.

11.2.3.3 TRAINING

This process must be clearly defined and understood by all of the personnel involved in the deicing process. Considerations should include, but are not limited to:

  1. Identification of aircraft critical surfaces;
  2. Frozen contaminant identification and inspection procedures;
  3. Definition and use of a "tactile" inspection;
  4. Tactile inspection techniques; and
  5. Pilot communications.

Initial and annual recurrent training of operators that will be conducting critical surface inspections is mandatory.

11.2.3.4 TRADITIONAL METHODS OF CONDUCTING A CRITICAL SURFACE INSPECTION

  1. Visual Inspection

    The Service Provider's personnel are required to visually inspect all critical surfaces to ensure that the aircraft is free of contamination prior to de/anti-icing, and prior to releasing the aircraft for departure. The aircrew may also need to inspect the representative surfaces (or the critical surfaces, where a representative surfaces is not designated) of the aircraft prior to take-off, in accordance with approved company procedures.

    It becomes more difficult, during night operations, during conditions of poor lighting and during inclement weather when visibility is substantially reduced, to achieve consistent results with visual inspections.

    While some forms of contamination, such as snow or ice pellets, can easily be detected through a visual inspection, other contamination such as clear ice can be extremely difficult to detect visually. The forms of contamination which are the more difficult to detect may require special inspection methods to ensure that an aircraft's critical surfaces are clean.
  2. Tactile Inspection

    The tactile inspection procedure requires that the Service Provider's personnel touch the leading edge of the aircraft's wings and/or other critical surfaces to establish that the aircraft is free of adhering contaminants.

    Service Providers requiring that their personnel expose their bare hands to de/anti-icing fluids, as may be the case for a tactile inspection, need to consider procedures for the protection of these personnel from the possible long term effects of such fluid exposure.

    The tactile inspection should be accomplished in a symmetrical manner.

    The tactile inspection is a good procedure for the detection of clear ice on the aircraft's critical surfaces both before and after deicing.

    On surfaces that are readily accessible, such as the leading edge, a tactile inspection can be accomplished with minimal disruption to the deicing operation. Other aircraft surfaces may present a formidable inspection challenge.
  3. Tactile Wand

    To address the issue of surfaces, which are difficult to reach, a pole may be used to perform the tactile inspection. This procedure must be well trained to ensure reliable results.

    The physical check is accomplished by moving the ice detection pole across the critical surface in a sweeping pattern. If the wing surface has a consistent texture, either rough or smooth, ice may be present and deicing may be required.

    As the pole is dragged across the inspection area, with ice present, a reduction in resistance of the pole to movement will be experienced. This is because the wing surface will have less friction. With ice present, the ice detection pole will glide smoothly over the entire surface.

    NOTE: Caution must be taken when using the pole to ensure that no damage is done to the aircraft.

11.2.4 Pre-take-off Contamination Inspection

The pre-take-off inspection should be accomplished shortly before the aircraft enters the active runway for take-off or before the pilot initiates the take-off roll; and is the final confirmation for the pilot that the aircraft is free of frozen contaminants. Components that can be inspected vary by aircraft design; which affects their visibility from the cockpit and/or cabin. The pilot may require the assistance of trained and qualified ground personnel to assist in the pre-take-off contamination inspection. On hard wing aircraft, in addition to visual inspection, a tactile inspection may be required.

The procedures to be followed, the surfaces to be inspected and the related actions to be accomplished by the pilot are all to be detailed in the approved ground icing program, where such a program is required (an approved program is mandatory for CAR705 Operators).

NOTE: In all circumstances this pre-take-off contamination must be conducted from outside of the aircraft if the Air Operator does not use the HOT guidelines.

11.2.4.1 INSPECTION IMMEDIATELY PRIOR TO TAKE OFF

Transport Canada's interpretation of the phrase "inspected immediately prior to take-off", in the ground icing context, is that the inspection must be conducted within five minutes prior to beginning the take-off roll.

Fluid testing has indicated that this procedure must not be applied to TypeI fluids. TypeI fluids have very short HOT values and fluid failure occurs suddenly. Therefore, it is not considered prudent to apply this procedure to TypeI fluids. The procedure should only be applied to TypesII, III and IV anti-icing fluids and then only when the pertinent minimum holdover time exceeds 20 minutes.

If, after conducting the pre take off contamination inspection once, it is not possible to take-off within five minutes, the aircraft must return for deicing. Additional inspections and time extensions are not considered prudent.

11.2.5 Representative Surfaces

11.2.5.1 REGULATORY STANDARD

GOFR622.11, sub-paragraph7.1.1.3, indicates the conditions under which Representative Surfaces may be approved for operational use.

11.2.5.2 FUNCTION OF REPRESENTATIVE SURFACES

  1. Particularly for large aircraft where very limited portions of the aircraft can be seen from inside, approved Representative Surfaces may be used to judge the condition of the aircraft's critical surfaces during ground icing conditions.
  2. Representative Surfaces are intended to be used, as a tool in gauging the contaminated state of critical surfaces on an aircraft after having used deicing and anti-icing fluids to clean the aircraft and then protect the aircraft from the freezing precipitation occurring during ground icing conditions.
  3. An aircraft's Representative Surface is a portion of the aircraft that can be readily and clearly observed by flight crew from inside the aircraft and is used to judge whether or not the surface has become contaminated. By determining the state of the Representative Surface, it can then be reasonably expected that other critical surfaces will be in the same (or better) condition.
  4. Prior to take-off, a visual check of the Representative Surfaces may be carried out by the Pilot-in-Command in command to ensure that contamination is not present at this stage of the flight; depending upon the requirements of the approved ground icing program. If conclusive, the aircraft may proceed to take-off, otherwise the aircraft must be de-iced again.

11.2.5.3 REPRESENTATIVE SURFACE APPROVAL GUIDELINES

  1. The choice of Representative Surfaces should first consider any recommendations made by the aircraft manufacturer.
  2. Operational and other pertinent experience can be very useful in choosing a Representative Surface. This is especially valuable when the Aircraft manufacturer hasn't offered any guidance on making the selection.
  3. If no Representative Surfaces have been identified by the aircraft manufacturer, an Air Operator may offer one or more Representative Surfaces for approval by the Regional Director, Air Carrier, or Chief, Airline Inspection, Transport Canada. Such a submission must be accompanied by the technical data supporting the use of these surfaces as representative for the aircraft type under consideration.
  4. Representative surfaces will normally be located on a critical surface of the aircraft.
  5. The surface being chosen should not be heated.
  6. The surface must be clearly visible and close enough for the viewer to determine that it is free of contamination. The location of the Representative Surface and the position inside the aircraft from which the surface is to be viewed must be specified for each aircraft type. This information must be clear and concise.
  7. If the surface is not adequately visible under all weather and lighting conditions, restrictions on its use must be clearly identified. Consideration should be given to locating Representative Surfaces in areas that can be illuminated by aircraft external lighting systems.
  8. Under some circumstances the presence of contrasting colours may be necessary in order to visually detect the presence of contamination. If a surface does not contain such contrast it may become necessary to paint a portion of the surface in contrasting colours to aid the flight crew.
  9. The Representative Surface should not be located in an area where the fluid tends to pool during anti-icing procedures. This fluid pooling would not result in the area being representative of the critical surfaces of the aircraft.
  10. Representative Surfaces should be designated for both sides of the aircraft in the event that weather and wind conditions are such that contamination is more likely to form on one side of the aircraft than on the other side of the aircraft.
  11. Representative surfaces that can be clearly observed by flight crew from inside the aircraft may be suitable for judging whether or not critical surfaces are contaminated.
  12. Research has indicated that fluid failure occurs last at the mid chord sections of wings. Therefore, whether painted or not, areas located at mid chord sections of wings and previously used for checking fluid conditions are not suitable alone for evaluating fluid failure and should no longer be used exclusively as Representative Surfaces. Portions of the leading and trailing edges of the wings should be included.
  13. Pre-take-off contamination inspections should concentrate on the leading edge in conjunction with the trailing edge of the wing. Dependent upon aircraft configuration, wing spoilers may also be used to provide an indication of fluid condition.

11.2.5.4 GUIDELINES ON THE USE OF REPRESENTATIVE SURFACES

  1. The Air Operator's Ground Icing Operations program must specify the ground and flight crew training to be conducted regarding the purpose, procedures and limitations with respect to Representative Surfaces. Training on the assessment procedures to be followed to determine whether or not the fluid has failed should be included in the program.
  2. This technique may be used when the aircraft manufacturer has identified Representative Surfaces which can be readily and clearly observed by flight crew during day and night operations, and which are suitable for judging whether or not critical surfaces are contaminated.
  3. Representative Surfaces may not be particularly effective during conditions when clear ice is forming on the aircraft's critical surfaces. Clear ice is even difficult to identify under ideal lighting conditions from outside the aircraft. Additional aircraft type specific procedures, such as tactile inspections, may be required.
  4. Other surfaces which are visible from inside the aircraft should also be inspected whenever possible, in addition to the Representative Surfaces. For example, under very good lighting conditions it may be possible to examine the surface of the wing beyond the Representative Surface.
  5. For large aircraft where it is necessary for one pilot to leave the flight deck in order to accomplish the pre-take off contamination inspection, there is the potential for the disruption of "checklist flow". The operator's ground icing plan should therefore specify at what point the inspection should take place in order to minimize any such disruption.
  6. Flight crew must be made aware that the use of Representative Surfaces for contamination detection may not be feasible in poor weather under very poor lighting conditions. The presence of contaminants on the cabin or cockpit windows may also make it difficult to properly observe the Representative Surfaces. Under conditions such as these it is prudent to have an external inspection conducted, to return for deicing and anti-icing or to delay the flight until conditions improve and a safe take off can be assured.
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