10. contaminated runways

10. CONTAMINATED RUNWAYS10. CONTAMINATED RUNWAYS

Performance JAR 25Performance JAR 25

CONTAMINATED RUNWAYSCONTAMINATED RUNWAYS

Definitions

Screen height

Distances

Takeoff charts

Example

DEFINITIONSDEFINITIONS

DRY RUNWAY

A dry runway is one which is neither wet nor contaminated, and includes those paved runways which have been specially prepared with grooves or porous pavement and maintained to retain ‘effectively dry’ braking action even when moisture is present.

DAMP RUNWAY

A runway is considered damp when the surface is not dry, but when the moisture on it does not give it a shiny appearance.

According to JAA regulations, a damp runway is considered dry as far as performance calculations are concerned. This may change in the future.


Damp runway


WET RUNWAY

A runway is considered wet when the runway surface is covered with water or equivalent, [with a depth less than or equal to 3 mm], or when there is a sufficient moisture on the runway surface to cause it to appear reflective, but without significant areas of standing water.

A wet runway has a shiny appearance, but without risk of hydroplaning.


Wet runway


CONTAMINATED RUNWAY

A runway is considered to be contaminated when more than 25% of the runway surface area within the required length and width being used is covered by the following:

Standing water: Caused by heavy rainfall and/or insufficient runway drainage with a depth of more than 3 mm (0.125 in).

Slush: Water saturated with snow, which spatters when stepping firmly on it.

Wet snow: If compacted by hand, snow will stick together and tend to form a snowball.

Dry snow: Snow can be blown if loose, or if compacted by hand, will fall apart again upon release.

Compacted snow: Snow has been compressed

Ice: The friction coefficient is 0.05 or below.


Contaminated runway


Equivalent of wet runway is runway covered with less than:

• 2 mm (0.08 inch) slush

• 3 mm (0.12 inch) standing water

• 4 mm (0.16 inch) wet snow

• 15 mm (0.59 inch) dry snow

SCREEN HEIGHTSCREEN HEIGHT

On wet and contaminated runways, the screen height is measured at 15 feet rather than 35 feet on dry runways. Moreover, the use of reverse thrust is allowed for ASD determination on wet and contaminated runways, whereas it is forbidden to take it into account for the ASD determination on dry runways.

Therefore, it is possible to obtain shorter TODs and ASDs on wet and contaminated runways than on dry runways for the same takeoff conditions. Thus, it is possible to obtain higher takeoff weights on surfaces covered with water, slush, or snow than on dry runways. This is why the regulation indicates that:

On a wet or contaminated runway, the takeoff mass must not exceed that permitted for a takeoff on a dry runway under the same conditions.

DISTANCESDISTANCES

ASD, TOD and TOR for wet runways are measured in the same way as for dry runways, except that the screen height is 15 ft and reverse thrust is considered.

TOD

15 ft

TAKEOFF CHARTSTAKEOFF CHARTS

Depending on the depth of water, we will use a different chart for takeoff performance calculations:

• Under 3 mm of water, use the WET RUNWAY correction.

• Between 3 mm and 6.3 mm, use the 6.3 mm (1/4 inch) WATER chart.

• Between 6.3 mm and 12.7 mm, use the 12.7 mm (1/2 inch) WATER chart.


Depending on the depth of slush, we will use a different chart for takeoff performance calculations:

• Under 2 mm of slush, use the WET RUNWAY correction.

• Between 2 mm and 6.3 mm, use the 6.3 mm (1/4 inch) SLUSH chart.

• Between 6.3 mm and 12.7 mm, use the 12.7 mm (1/2 inch) SLUSH chart.

For compacted snow, a special chart is provided (COMPACTED SNOW).


Equivalent of wet runway is runway covered with less than:

• 2 mm (0.08 inch) slush

• 3 mm (0.12 inch) standing water

• 4 mm (0.16 inch) wet snow

• 15 mm (0.59 inch) dry snow


We have to main targets:

1. Determine PTOW.

2. Determine V1, VR and V2.

Remember that flexible takeoff is not allowed when taking off from a contaminated runway.

In most aircraft, thrust reverse, anti-skid system and ground spoilers must be operative in order to takeoff from a contaminated runway. For a wet runway, reverse thrust is not required.

Since runway contamination will affect braking much more than acceleration, the ASD will increase much more than the TOD as well. As a result, takeoff speeds will be lower than those for a dry runway.


How to calculate PTOW:

1. Calculate the PTOW for dry runway (for each configuration), and correct it by QNH and bleed.

2. Determine the weight penalty on the appropriate chart for each configuration.

3. Apply corrections to the PTOWs calculated on (1) and choose the configuration that gives the highest PTOW.


How to calculate takeoff speeds:

1. With the configuration and ATOW, use the appropriate chart to find takeoff speeds.

EXAMPLEEXAMPLE

Let’s calculate PTOW and takeoff speeds with this conditions:

• LFPO Runway 08

• TORA: 3320 m

• Runway covered with 7 mm slush

• PTOW (dry): 72000 Kg (CONF 1+F)

71100 Kg (CONF 2)

71200 Kg (CONF 3)

We will use the 12.7 mm slush chart

EXAMPLEEXAMPLE

EXAMPLEEXAMPLE

EXAMPLEEXAMPLE

V1 = 124 ; VR = 133 ; V2 = 133

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10. contaminated runways