Contaminated Runways

Contaminated Runways

A contaminated runway dramatically alters friction coefficient, take-off distance, landing distance, and controllability. The pilot must know the runway condition before every flight and plan accordingly.

Source: ICAO Annex 14 Vol I Aerodrome Design and Operations; ICAO Doc 9981 PANS-Aerodromes; EU Regulation 139/2014 (Aerodromes) Annex II ADR.OPS.B; FAA AC 91-79A Mitigating the Risks of a Runway Overrun upon Landing; EASA NPA 2016-11 and EASA Decision 2018/014/R Runway Surface Condition Assessment and Reporting (Global Reporting Format — GRF).

Definition (EASA / ICAO)

A runway is considered contaminated when more than 25 % of the required length and width of the runway portion being used is covered by:

• Standing water more than 3 mm deep
• Slush (ice-water-snow mix) more than 3 mm deep
• Loose snow
• Wet snow
• Compacted snow
• Ice

Before 2018, other thresholds were sometimes used; since GRF (Global Reporting Format, 2021 worldwide) the uniform reference is 3 mm for water/slush, and ICAO standardises reporting in RWYCC (Runway Condition Code 0–6).

Main hazards

Increased rolling resistance on take-off

• Rain and wet snow: increase rolling resistance → longer take-off roll.
• Slush: additional weight through spray, higher tire friction, possible icing of wheels/flaps.
• Wet grass: noticeably increases take-off AND landing distance (typically +25–30 % vs dry grass).

Slush icing on take-off

• Sprayed slush can freeze on fuselage and control surfaces.
• Flaps, tailplane, ailerons may stiffen.
• → Before take-off roll, minimise slush exposure (avoid runway or other sector).
• After lift-off no flap retract until icing ruled out.

Aquaplaning (hydroplaning) on landing

• On a wet runway after heavy rain: tire "floats" on water film, no braking, no steering.
• Aquaplaning speed (NASA rule of thumb): Vaqua [kt] ≈ 9 × √(tire pressure [psi]). Example C172 ~31 psi → ≈ 50 kt — typically no aquaplaning below 50 kt, possible above.
• Symptoms: brakes ineffective, steering lost, aircraft slides.

Braking technique under aquaplaning suspicion

1. Brake moderately — no hard braking (wheels lock, no friction contact).
2. Aerodynamic control maintained: ailerons, elevator, rudder still work.
3. Maintain direction via aerodynamic means.
4. Wait for friction contact — once water film reduces (rougher runway end, tire warming), braking takes effect.

Snow-covered runway

Vision problem (flare)

• Snow covers runway markings and visual cues for flare height.
• Pilot may misjudge height → touchdown too low or too early → swing-off (lateral drift).

Take-off on snow

• Longer TO distance due to friction.
• Flaps as POH soft-field take-off (typically 10°).
• Yoke fully back during roll.

Landing on snow

• Touchdown at minimum speed.
• Flaps fully extended (max lift, lowest touchdown speed).
• Yoke fully held back during roll-out — nose up, less rolling resistance.
• Brakes sparingly — aerodynamic braking dominant.

Wet grass

• Extended take-off AND landing distance (typically +25–30 % vs dry grass).
• On short runway critical: check TODR vs TODA.
• Landing on wet short grass: full flaps, touchdown at minimum speed, yoke fully held back.

Pre-flight check of runway conditions

• Check AIP / NOTAM for RWYCC / SNOWTAM.
• METAR (RWY friction coefficient with snow/ice).
• Phone call to AFIS / Tower before approach at unfamiliar fields.
• POH performance for non-dry runways — many POHs have correction factors for wet/contaminated runways.

Performance impact — order of magnitude

Source: typical POH correction factors (e.g. C172 Pilot's Operating Handbook); each aircraft has its own values — always consult the POH.

Practical consequences

• On slush or ice runway: consider diversion to a dry runway.
• On wet grass + short runway: TODR often longer than TODA → do not take off.
• Aquaplaning risk after rain: land in runway centre with adequate final speed, brake moderately.
• Pilot in Command decides — when in doubt, divert or wait.