Wet and Contaminated Runway Performance

Runway Surface Classifications

• Dry Runway: No visible moisture or contamination. May include grooved or porous surfaces designed to maintain dry-like friction even when slightly damp.
• Wet Runway: Surface is covered by water, slush, or snow up to 3 mm deep, or appears reflective but without significant standing water. Not considered contaminated but offers less friction than dry.
• Contaminated Runway: More than 25% of the runway surface is covered by water, slush, snow, or ice exceeding 3 mm in depth (or equivalent). This includes standing water, slush, wet/dry/compacted snow, ice, frost, and specially prepared winter surfaces.

Types of Contamination

• Standing Water: More than 3 mm deep.
• Slush: Water-saturated snow that splashes when stepped on.
• Wet Snow: Moist snow forming a compact ball but not releasing water.
• Dry Snow: Powdery, non-cohesive snow.
• Compacted Snow: Densified, solid snow with minimal further compression.
• Ice and Frost: Solid or granular frozen surfaces, extremely slippery.
• Specially Prepared Winter Runway: Treated, frozen surfaces with enhanced friction.

Performance Effects

• Take-off and Landing: Both distances increase on wet or contaminated runways due to reduced friction and increased drag.
• Braking: Significantly less effective, especially on ice or slush, increasing accelerate-stop distances.
• Hydroplaning: Two speeds are relevant—dynamic hydroplaning (where tyres ride on a water film) and viscous hydroplaning (thin film loss of friction). Dynamic hydroplaning is the most limiting for wet runway operations.

Hazards and Management

• Hazards: Reduced braking, loss of directional control, increased risk of runway excursions.
• Management: Prefer delaying operations until the runway is clear. If not possible, apply manufacturer performance corrections, consider increased distances, and follow operator procedures. Special crew training and operational restrictions may be required for frequent contaminated runway use.

Derated Take-off and Wet V1

• Derated Take-off: Using less than maximum thrust on contaminated runways can be beneficial for engine longevity but must not compromise performance margins.
• Wet V1: A reduced V1 (decision speed) may be used to account for longer stopping distances, but using a wet V1 on a dry runway can unnecessarily limit performance.