Uncleaned rubber deposits in the touchdown zone result in the runway surface to be slippery-when-wet.
Landing on Wet or Contaminated Runway
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AIRBUS INDUSTRIE
Flight Operations Support
Factors and Effects
Braking action:
The presence of fluid contaminant (i.e., standing water, slush or loose snow) or hard contaminant (i.e., compacted snow or ice) on the runway adversely affects the braking performance (stopping force) by:
. Reducing the friction force between the tires and the runway surface.
The reduction of friction force depends on the following factors:
. tire tread condition (wear) and inflation pressure;
. type of runway surface; and,
. anti-skid system performance.
.
Creating a fluid layer between the tires and the runway surface, thus reducing the contact area and creating a risk of hydroplaning (i.e., complete loss of contact and friction between the tires and the runway surface).
Fluid contaminants (such as standing water, slush or loose snow) also positively contribute to the stopping force at landing by:
.
Resisting to the wheels forward movement, thus causing a displacement drag;
.
Creating a spray pattern that strikes the landing gears and airframe, thus causing an impingement drag.
Certification regulations require the spray pattern to be diverted away from engine air inlets to prevent affecting engine performance.
The braking action is the net effect of the above stopping forces (as illustrated by Figure 1 and Figure 2).
Hydroplaning (aquaplaning):
Hydroplaning occurs when the tire cannot squeeze any more of the fluid contaminant layer between its tread and the runway surface; the tire lifts from the runway surface and surfs the wave of water.
Getting to Grips with Approach-and-Landing Accidents Reduction
Hydroplaning results in a partial or total reduction of contact surface between the tire and the runway and in a corresponding loss of friction coefficient.
Main-wheels and nose-wheels equally can be affected by hydroplaning, thus affecting the braking performance and the effectiveness of the nose-wheel-steering.
Hydroplaning always occurs in some degree when operating on a fluid-contaminated runway.
The potential for severe hydroplaning directly depends on the following factors:
.
Absence of runway surface roughness and drainage (e.g., transverse saw-cut grooves);
.
Thickness and nature (e.g., water or slush) of the fluid contaminant layer;
.
Tire inflation pressure;
.
Ground speed; and,
.
Antiskid operation (e.g., locked-wheel case).
A minimum hydroplaning speed can be defined for each aircraft type and runway contaminant.
Hydroplaning may occur at touchdown, preventing the wheels from spinning and from sending the wheel-rotation-signal to various aircraft systems.
Performing a firm touchdown can prevent hydroplaning at touchdown and ensure rotation of main-landing-gear wheels.
Directional control:
On contaminated runway, directional control should be maintained using rudder pedals (do not use nose-wheel-steering tiller until aircraft has slowed down to taxi speed).
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