Contaminated Surface

[AltFlaps]

Hi All,

I'm trying to find an all encompassing definition of a 'contaminated surface'.

Does anybody know where I might find the 'official definition' (assuming there is one of course)

Thanks

AF

[Brian Fantana]

The only definition i have read about is:

Contaminated runway - when 25% of runway covered by,surface water more than 3mm deep or slush/loose snow equivalent to more than 3mm of water, compacted snow or ice.

If that helps?

[FlyboyUK]

A runway is considered to be contaminated when it has more than 25% of its surface area (whether isolated areas or not) within the required length and width being used covered by the following:

1. Surface water more than 3mm deep
2. Slush or loose snow with a water equivalent depth (WED) more than 3mm
3. Snow which has been compressed into a solid mass which resists further compression and will hold together or break into lumps, if picked up (compacted snow)
4. Ice, or wet ice

JAR-Ops 1.480(2)

Hope that helps :ok:

[prometheusracer]

Hmm, so nothing about gravel, fluids, bits of a/c then....:}

[AltFlaps]

Thanks everybody, thats what I was looking for ...

Cheers

AF

[tribo]

http://www.easa.eu.int/doc/Agency_Mesures/Agency_Decisions/CS-25%20Consolidated%20version.pdf
AMC 25.1591
The derivation and methodology of performance information for use when taking-off and landing with contaminated runway surface conditions.
1.0 Purpose
This AMC provides information, guidelines, recommendations and acceptable means of compliance for use by applicants in the production of performance information for aeroplanes when operated on runways that are contaminated by standing water, slush, snow, ice or other contaminants.
2.0 Technical Limitations of Data
The methodology specified in this AMC provides one acceptable means of compliance with the provisions of CS 25.1591. In general it does not require aeroplane testing on contaminated runway surfaces, although such testing if carried out at the discretion of the applicant may significantly improve the quality of the result or reduce the quantity of analytical work required.
Due to the nature of naturally occurring runway contaminants and difficulties associated with measuring aeroplane performance on such surfaces, any data that is either calculated or measured is subject to limitations with regard to validity. Consequently the extent of applicability should be clearly stated.
The properties specified in this AMC for various contaminants are derived from a review of the available test and research data and are considered to be acceptable for use by applicants. This is not an implied prohibition of data for other conditions or that other conditions do not exist.
It has been recently determined that the assumption to use wet runway surface field length performance data for operations on runway surfaces contaminated with dry snow (depths below 10 mm) and wet snow (depths below 5 mm) may be inappropriate. Flight test evidence together with estimations have indicated some measure of relatively low gear displacement
drag and a measurable reduction in surface friction in comparison to the assumptions associated with wet runway field performance data. As a consequence it has been agreed that additional work is required to further develop the associated methodology. As an interim measure it has been concluded that it is reasonable to consider these surfaces by recommending that they be addressed by using the data for the lowest depth of the
contaminant provided.
It is intended that the use of aeroplane performance data for contaminated runway conditions produced in accordance with CS 25.1591 should include recommendations associated with the operational use of the data. Where possible, this operational guidance should be provided by the applicant or its production co-ordinated with the applicant to ensure that its use remains
valid.
Operators are expected to make careful and conservative judgments in selecting the appropriate performance data to use for operations on contaminated runways. Particular attention should be paid to the presence of any contaminant in the critical high speed portion of the runway. For takeoff, it may be appropriate to use different contaminant types or depths
for the takeoff and the accelerate-stop portions. For example, it may be appropriate to use a greater contaminant depth or a contaminant type that has a more detrimental effect on acceleration for the takeoff portion than for the accelerate-stop portion of the takeoff analysis.
In considering the maximum depth of runway contaminants it may be necessary to take account of the maximum depth for which the engine air intakes have been shown to be free of ingesting hazardous quantities of water in accordance with CS 25.1091(d)(2).
3.0 Standard Assumptions
Due to the wide variation in possible conditions when operating on contaminated runways and the limitations inherent in representing the effects of these conditions analytically, it is not possible to produce performance data that will precisely correlate with each specific operation on a contaminated surface. Instead, the performance data should be determined for a standardised set of conditions that will generally and conservatively represent the variety of contaminated runway conditions occurring in service.
It should be assumed that:
- the contaminant is spread over the entire runway surface to an even depth (although rutting, for example, may have taken place).
- the contaminant is of a uniform specific gravity.
- where the contaminant has been sanded, graded (mechanically levelled) or otherwise treated before use, that it has been done in accordance with agreed national procedures.
4.0 Definitions
These definitions may be different to those used by other sources but are considered appropriate for producing acceptable performance data, suitable for use in aeroplane operations.
4.1 Standing Water
Water of a depth greater than 3mm. A surface condition where there is a layer of water of 3mm or less is considered wet for which AMC 25.1591 is not applicable.
4.2 Slush
Partly melted snow or ice with a high water content, from which water can readily flow, with an assumed specific gravity of 0.85. Slush is normally a transient condition found only at temperatures close to 0°C.
4.3 Wet Snow
Snow that will stick together when compressed, but will not readily allow water to flow from it when squeezed, with an assumed specific gravity of 0.5.
4.4 Dry Snow
Fresh snow that can be blown, or, if compacted by hand, will fall apart upon release (also commonly referred to as loose snow), with an assumed specific gravity of 0.2. The assumption with respect to specific gravity is not applicable to snow which has been subjected to the natural ageing process.
4.5 Compacted Snow
Snow which has been compressed into a solid mass such that the aeroplane wheels, at representative operating pressures and loadings, will run on the surface without causing significant rutting.
4.6 Ice
Water which has frozen on the runway surface, including the condition where
compacted snow transitions to a polished ice surface.
4.7 Specially Prepared Winter Runway
A runway, with a dry frozen surface of compacted snow and/or ice which has been treated with sand or grit or has been mechanically or chemically treated to improve runway friction. The runway friction is measured and reported on a regular basis in accordance with national procedures.
4.8 Specific Gravity
The density of the contaminant divided by the density of water.

[keithl]

AltFlaps a topical question, indeed, as I have just received the new issue of the relevant AIC (as I see you are based in UK). It is 3/2007 dated 4 January.

Interestingly, in relation to the "slippery at BRS" thread, it contains the statement, "slippery when wet" is not to be confused with "icy".

[WHBM]

Interesting to make such a Contaminated Runway departure at St Petersburg in a BA A320. It had been snowing all day and the runway, although adequately cleared, was still dusted all over. So full power and a notably short take-off run.

Contrast to Dublin a few years ago where a rare snowstorm had caused disruption. The runway was absolutely clear but there was further delay at the hold just while they removed some snow trails left by a preceding aircraft's tyres, which seemed trivial.