A320 & Contamined Runways
 

Hi everybody,

I've a few questions concerning operations on contamined runways with A320. In the FCOM performance calculations for take off and landing are done only as a function of type of contamination and depth. Friction coefficient is taken into consideration only for max xwind limit.

- Why in the FCOM there're no performance calculations as a function of the friction coefficient? is it because the certification requirements don't call for it?

- It may happen to plan a take off from a runway covered for instance with 2mm of dry snow and a reported friction coefficient below 0,25. From the performance point of view this type and depth of contamination is equivalent to a wet runway but for sure the runway distance required to stop the a/c in case of RTO would be much higher. What's the best way to do a precise planning in these conditions?

Thanks

che, I would expect that the contaminated data is based on the requirements in CS 25 Large Aircraft; see page 665 onwards, AMC 25.1591.

Essentially, there is no correlation with a measured Mu and aircraft performance, thus distance tables relate to the observed conditions – contaminant and depth. However, even with these items for guidance there could be a wide range of error.
The AMC explains the background, and rather technically the assumptions and resultant risks of operating in contaminated conditions. Best advice is don’t operate.

Re takeoff on snow. The aircraft performance data would probably allow such an operation; however with the reported Mu (unofficial / unreliable) to aid judgment the operation could have high risk. If (IF) the value of Mu was correct, then the runway braking action (ICAO) would be described as poor to nil – possibly something equivalent to ‘flooded’ or wet ice. ( Managing Threats and Errors During Approach and Landing slide 26). Thus, it would be unwise to operate without some other clarifying data, e.g. specific gravity of contaminant.

Refs:
Runway Operations - Risks and Factors Associated with Operations on Runways Affected by Snow, Slush or Water.

Takeoff / Landing on Wet, Contaminated and Slippery Runways.

There is one condition in which measured grip can be used. That is when the runway contaminant is compacted snow or ice. Under these conditions reported figures can be looked up in the Snow & Ice Tables.

Otherwise, Safetypee speak with straight tongue:)

In Europe, I would ask for a delay and make sure the authorities got busy with the snow team. Is 1 hour of your time worth risking it?

Sir George Cayley