Chapter 5 - Ground Crew Supplement

Guidelines on the Use of Representative Surfaces

35.  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.

36.  This technique may be used when the aircraft manufacturer has identified representative aircraft 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.

37.  When the aircraft is deiced and anti-iced, it is desirable for the representative surface to be treated first during the final application of fluid. Whether or not this procedural methodology is appropriate for any particular aircraft design needs to be determined.

38.  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.

39.  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.

40.  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.

41.  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.

42.  Air Operators that have established a program in accordance with TC Ground Icing Operations Standards may have representative aircraft surfaces designated and approved for their aircraft. 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.

43.  Many operators have painted a portion of the representative surface in a darker colour to aid in the visual detection of contamination. Some have designated representative surfaces on both sides of the aircraft in the event that, due to strong wind during taxi, one side of the aircraft becomes contaminated before the other.

44.  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 for evaluating fluid failure and should no longer be used exclusively as representative surfaces. Tests have shown that first fluid failure occurs in the areas of the leading and trailing edges on aircraft with leading edge devices and that first fluid failure occurs in the areas of the spoilers, wing tip and the trailing edges on hard wing aircraft. (Note:  The leading edges should always be checked because they are critical to aircraft performance.)

45.  Pre-take-off contamination inspections should be concentrated on the leading edge close to the fuselage (the wing high lift area) and ahead of the aileron (the roll control area) where these are visible. Dependent upon aircraft configuration, wing spoilers may also be used to provide an indication of fluid condition.

46.  In addition to the representative surface, other aircraft critical surfaces which are visible from inside the aircraft should be inspected for contamination whenever possible.

47.  The operational advantage of a check from inside the aircraft is obvious in this circumstance. However, as stated in the TC standard, the operator's program must specify the conditions, such as weather, lighting and visibility under which such an inspection may be conducted. In some cases, even the presence of residual deicing and anti-ice fluid on cabin windows may make a proper visual check difficult or impossible.

48.  In any event, flight crew personnel should be aware that the use of a representative surface for contamination detection might not be feasible in some circumstances. A return to the deicing facility will be the only safe alternative, if any doubts exist, regarding the condition of the aircraft.

The decision to take off following the pre-take-off inspection is the responsibility of the PIC.