The presence on the runway of a fluid contaminant (water, slush or loose snow) or a solid contaminant (compacted snow or ice) adversely affects braking performance (stopping foce) by:

• Reducing the friction force between the tires and the runway surface; and
• Creating a layer of fluid between the tires and the runway, thus reducing the contact area and creating a risk of hydroplanning (partial or total loss of contact and friction between the tires and the runway surface).

When grass is wet, it becomes slippery and offers less friction. During take-off, the aircraft relies on the friction between its tires and the ground to accelerate. Reduced friction means the aircraft requires a longer distance to reach the necessary speed for lift-off, thus, increasing the take-off distance.

Similarly, during landing, the aircraft requires more distance to decelerate due to the reduced braking efficiency on the slippery surface, resulting in an increased landing distance.