Representative Aircraft Surfaces


Representative surfaces that can be clearly observed by the crew from inside the aircraft may be suitable for judging whether or not critical surfaces are contaminated. Guidelines for the approval of representative surfaces have been developed.


Many operators have painted a portion of the representative surface in a darker color 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.


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.


Pre-take-off contamination inspections should be concentrated 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.


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


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


Effects of Aircraft Surface Contamination:


Any contamination (ice, dirt, etc.) with the roughness similar to medium sandpaper adhering to an aircraft wing surface has the potential to reduce the lift by at least 20%. Adhering contamination can affect the aircraft acceleration on the ground and during rotation because of the increased weight and changing the airfoil shape.


“If frozen deposits are present, other than those considered in the certification process, the airworthiness of the aircraft may be invalid and no attempt should be made to fly the aircraft until it has been restored to the ‘clean’ configuration”.


Sensing Contamination


Some new generation aircraft have onboard sensing components. However, the oldest and most reliable


“sensor” is the crewmember. Seeing and anticipating is the best method. This is a function of the entire crew. It can incorporate the entire team, passengers, other aircraft reports, ground crew, etc. When everyone is encouraged to speak up when they see or feel some abnormality, the crew is practicing the highest degree of Crew Resource Management. You should encourage everyone to be empowered to speak up when something isn’t right.


In flight, turning the auto pilot off may help sensing by the feel of sluggish or heavy controls. Sometimes an aircraft buffet can be felt. Often, crewmembers can hear a sound change when the airflow pattern changes with contamination formation on aircraft surfaces.


Contamination Removal on the Ground


Contamination removal while the aircraft is on the ground is usually referred to as “deicing”. This is done by utilizing a heated hangar, ropes, squeegees, hot fluid under pressure (forceful stream through a nozzle), hot water, hot air, etc.


Anti-icing is the process where unheated glycol is sprayed on a clean aircraft to keep contamination from occurring or reoccurring. This is usually a type II, III or IV fluid. Deicing/Anti-icing fluids are either ethylene or propylene glycol.


This is a one-step or a two-step procedure. The one- step procedure is accomplished for deicing by using either Type I, II, III, or IV fluids usually applied hot, though may be applied at ambient temperature to remove the contaminant.


The two-step procedure has two distinct steps. The first step, deicing, is followed by the second step, anti- icing, which is a separate fluid application on the clean aircraft surface. The two-step procedure provides the longest holdover times (HOT).


Surface Contamination 8


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