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Specially treated runways

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Specially treated runways

Old 7th Jan 2015, 18:56
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Specially treated runways

Can anyone point me to some good articles about performance on specially prepared winter runways? I had my first experience on a sanded runway in Sweden today and our only advice is to downgrade the braking action given by one category - so Medium/good is treated as medium.

There is no advice on what to do if you get other contaminants on top - if it is snowing on arrival for example can one accept any contaminant on top, and what braking action might one use? Or do you wait for the runway to be cleared or go elsewhere?

I was pleasantly surprised by how good the braking action was in general though - definitely better than some wet runways I've landed on.
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Old 8th Jan 2015, 09:36
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Specially treated runways

There's a contaminated rwy, with accompanying performance. Now u treat it (or treat it specially😝), and now we have to degrade the performance 1 category. Am I missing something?
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Old 8th Jan 2015, 10:10
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JeroenC, specially treated runways fell outside the scope of many TALPA matrix introduced by airlines in the last 12 months.
Author is clearly referring to a TALPA matrix where these type of runways are included.
It indeed states to treat them as such.
Similarly it does not cover post treatment changes like new snowfall on top.
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Old 8th Jan 2015, 13:55
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Skyjob is correct - I should have mentioned the magical new TALPA. Our advice for specially prepared runways is to downgrade the measured braking action one level, but that's it.

It's basically an ice surface that has been sanded, so I don't know what kind of contaminants you are allowed on it. For snow on Ice, or ice in general, TALPA prohibits landing for example. Am I allowed say 1mm of snow on top of a prepared runway? If so, what braking action should I plan for? Am I even legal to attempt a landing? Our books are silent on all these questions and would be interested if anyone has any answers.
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Old 8th Jan 2015, 18:46
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Jwscud, a minor but perhaps important point is that a primary aim of TALPA is to replace measured friction as a means of reporting because it is unreliable. Thus your point might be to degrade the declared braking action by 1 for sand, not the measured value, because they might not be the same.

However, where the braking action is based on the type and depth of contaminant as in TALPA, sand is not considered except as noted: While applying sand or liquid anti ice to a surface may improve its friction capability, no credit is taken until pilot braking action reports improve or the contaminant type changes (e.g., ice to water). This is interesting because pilot braking action reports in TALPA, presumably PIREPS, should not be used to upgrade the braking action, only downgrade them.

From the FAA briefing on TALPA trials (33rd Annual Airport Conference), Pilot reports are divided fairly equally in their opinions of sanding/treating the runway improves or doesnt make a significant difference in the braking action that they experience for the contaminant conditions reported.

Thus via TAPLA, sand may not/does not change the braking action, but as yet there is no means of assessing the braking action of a sanded runway except by using mu meters which can be unreliable.
Yet again the regulators place the responsibility for safety on the operator, but without advice to help them.


ICAO Circular 329 considers sand thus:- the effect of non-melting ice conditions can vary considerably depending on the smoothness of the surface, whether it has been treated with sand or melting agents etc.
Elsewhere it discusses sand as a contaminant (presumably on a hard surface) which degrades the braking action.

FAA AC 150/5200-30C discusses the use of sand but offers little operational advice: sands do not perform the same. In general, the greater the quantity of sand applied, the greater the increase in traction. Fine sands show superior performance on warmer ice (>20 F (-7 C)), while coarser sands show superior performance on colder ice (<15 F (-9 C))".


Thus downgrading the braking action by 1 seems a good policy, but if the downgrade gives poor to nil, should you operate.
Also, what is the basis of the reported braking action; is this before/after sanding, and by what means was it obtained.
Other references to sanding appear to be from local authorities (Sweeden); what is the view of the certificating (AOC) national authority (UK)?
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Old 9th Jan 2015, 11:38
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PEI_3721 - thank you. That was exactly the sort of stuff I was after. Our overriding authority is EU OPS, which says nothing really except giving basic definitions and that "appropriate performance data must be available".

Our company TALPA matrix for specially prepared runways only says that the measured friction must be downgraded one category and the performance done no that basis. Obviously if there are other contaminants on top, as we have no figures we are not legal to attempt a landing or takeoff, so need to wait for it all to be cleared.

The airport in question was Skellefte (ESNS) but I haven't found much in the Swedish AIP or AICs either.
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Old 9th Jan 2015, 13:22
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Jw,
What next, you might dare to ask the authority what is appropriate – either operators/manufacturer’s judgement or don’t do it at all.

Checking CS 25 AMC 25.1591(~page 665) ‘The derivation and methodology of performance information for use when taking-off and landing with contaminated runway surface conditions’, which is primarily guidance for manufacturers, but has information relevant to operations.

Some of the important points are: “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”.
Hence good risk mitigation by downgrading the reported braking action.


Re sand (definitons): “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.”
N.B. this conflicts with TALPAs means of determining braking action vs ‘friction’
“The responsibility for relating this data to a friction index measured by a ground friction device will fall on the operator and the operating authority.”
There is also a note on the default values of friction (assumptions used in perf calcs) “Note: For a specially prepared winter runway surface no default friction value can be given due to the diversity of conditions that will apply.”

And the final ‘catch all’ which appears to be the basis of UKCAA airfield policy; “Operation on runways contaminated with water, slush, snow, ice or other contaminants implies uncertainties with regard to runway friction and contaminant drag and therefore to the achievable performance and control of the aeroplane during take-off, since the actual conditions may not completely match the assumptions on which the performance information is based. Where possible, every effort should be made to ensure that the runway surface is cleared of any significant contamination.”


The whole section of the AMC is well worth reading, if only to enlighten management as to some of the risks in such operations.
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Old 16th Jan 2015, 13:41
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Further to the discussion, see the recent Airbus briefing and recommendations on 'Landing on Contaminated Runways'. The article provides practical guidance which complements previous articles on TALPA and OLD/FOLD in ‘Safety First’.
Well done Airbus. Safety First, Jan 2015.
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Old 16th Jan 2015, 18:36
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Is it not the case that this is a very new process in its infancy, with all the inherent inaccuracies thereof? We are in aviation, an ever evolving environment. This is one such area that is not an exact engineering science, like much of our nuts & bolts and aerodynamics we are used to. I'm sure there will be much try & test it follow up research after data is examined; much suck it and see and we learn from it scenarios. It is the beginning of a whole new experiment. Let's treat it as such and take a strong modicum of care in your decision making. It's all only guidance; there are no guarantees, just like with there old system. It is not an RTOW equivalent for landing.
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