Contaminated Performance @3mm?

[Bamboid]

Query regarding contaminated performance, specifically the cut-off point from wet to contaminated @/around the 3mm mark.

EU-OPS 1.480(a)2.(i) specifies that 'contaminated' is defined as when the contaminant is present to a depth of '>3mm'.

EU-OPS 1.480(a)10. defines 'wet' as when the contaminant is present at a depth less than 'para (a)2 above'.

My query is, when the depth is reported as EQUAL to 3mm, would EU-OPS class this as contaminated or wet?

[100above]

Just been reading up on this today and as far as I can see, the second line relates to a depth less than the first line which was >3mm. An exact depth of 3mm is less than the >3mm figure on the first line and is therefore considered wet.

[pensador]

I am fully agree with 100above, it is very logically and from the very different manuals of different aircrafts we can see that 3mm is equal to wet
Con respecto

[Meikleour]

Many years ago whilst doing a study for an airworthiness group I was given the opportunity to inspect, various runway surfaces. The thing that struck me most at the time was, since many runways are surfaced with `macro-porous` surfaces to allow the fluid to run down through the top layer and concrete ones are often grooved - it is in practice almost impossible to accurately measure 3mm of fluid!

Be very wary of treating figures of wet contamination too literally.

[PEI_3721]

If, when you stamp your foot on the ground the water splashes up, consider the surface contaminated – depending on the area covered.
Pre departure, get the first officer to do the test.
Before landing use ATC, line maintenance, etc, etc; OK we should use the official reports but every bit of info helps.

A further problem with the condition of the runway is how to correlate the range of wet surfaces with the landing performance. The baseline friction value might only apply to a thin film of water – depending on surface texture, but what is the loss of performance between that and 3mm (contaminated)?
On a ‘WET’ runway it’s useful to check the landing distance required for both wet and contaminated conditions, the latter particularly important for non-grooved and rubber contaminated surfaces. You can then choose one or the other or a safety buffering middle value.

[towser]

Can a grooved runway ever be considered wet? The whole point of the grooves is to drain the water away isn't it?

[PEI_3721]

Can a grooved runway ever be considered wet?
IMHO, yes. Any runway which has a reflective appearance should be considered wet.
Even if grooves or a porous surface are designed to keep the surface well drained, they can be blocked with dust, dirt, rubber, etc, or ‘dammed’ by crosswinds.

I recall that JAR-OPS did allow a dispensation for a wet grooved runway to be considered as dry, by equally my memory suggest that this has been repealed. Similarly I cannot find any reference in EU-OPS 1, neither any guidance material (AMC) for the latter document.

Background refs; UK AICs 14/2006, and 86/2007

[Sepp]

PEI_3721 Take a peek at OPS 1.480 (a) (4).

Also, for UK drivers (I suppose it's all good stuff for visitors to our shores, too), FODCOM 2009/03 addresses the issue - and refers to the above OPS reg.

http://www.caa.co.uk/docs/33/FOD200903.pdf

Cheers!

[PEI_3721]

Thanks Sepp; that’s the material I was thinking of.
So the UK CAA ‘suggests’ (not overruling EU OPS) that in the UK wet grooves are not dry, and that UK operators should consider the same throughout Europe ??

The key to the EU case appears to be in the small print – 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.

So exactly how are crews expected to know if a runway is correctly maintained, – perhaps via the runway friction maintenance assessment? But that’s primarily for wet runways, and where the maintenance friction is below a set value, the runway should be declared ‘Slippery when wet’ (NOTAM)
In the absence of operational guidance for the term ‘Slippery when wet’ (it’s the operators responsibility – UK AIP sect AD 1.1.1, para 16), a good working level guide is to use contaminated performance data on a wet ‘Slippery when wet’ runway.

But the discussion is for dry equivalence on a wet grooved runway, so the use of wet data vice dry for reported poor maintenance (on a wet grooved runway) may be insufficient protection because the runway could be ‘Slippery when wet’. Thus, a jump straight to contaminated data might be logical.

I think that this conundrum starts with the use of “effectively dry”. AFAIK, this term is not defined, nor is moisture in CS 25 (origin of performance) and the UK AIP definition differs from EU-OPS (change of colour vs shiny appearance).
So should operators take “effectively dry” a being exactly the same a dry, or perhaps as the UK CAA infers in the FODCOM … there aint no such thing as a ‘dry’ wet grooved runway. But still like the EU, they dump the responsibility back on to the operator, which no doubt falls on the pilot of the day.

As above, IMHO, a wet grooved runway is always wet, and a runway which is ‘Slippery when wet’ is contaminated.
And for a wet runway, how wet is WET – 2.9 mm or 3 mm equivalent? So assess both wet and contaminated data in order to have guidance on the range of likely performance.

[Ocampo]

Sounds like pilot's good judgement is called for those marginal cases.

Keeping in mind also that not everywhere you can get such detailed information to make the "right" (or the lawyer's) choice...

I was taught to always go to the safe side instead of having little chances or (margins) to err. Especially when it comes to runways; so I'd take "contaminated" figures please.

Asking the ATC for the runway status, also other landed aircraft and some dispatcher on the ops frequency seems a good deal for me. Adding that to what you can see through the windshield (if that's somehow possible...), the METAR and/or a TAF seems about enough to make an educated decision.

You might also land a bit before the aiming points if conditions permit, that way you can get some extra feet just in case. Although I reckon that if you need those extra feet, probably there's something wrong with your numbers :O

There's always the possibility of a missed approach if you count one too many centre lights passing by...

[PEI_3721]

Adding to #9.
I must stress that when comparing wet and contaminated data, the information is not necessarily 'like-for-like'.
Wet landing performance includes a runway distance safety factor (1.92), and normally does not assume the use of reverse thrust; as conditions deteriorate the safety margins reduce rapidly, i.e. we might depend more on reverse.
Contaminated data under EU rules most likely assumes reverse thrust (see AFM), and the data might only have a distance safety factor of 1.15 (EU-OPS 1.520).
Thus in extreme conditions, whilst the published distances for wet and contaminated landings could have similar values (contaminated must not be less than wet), the basis of the calculation, safety margins, and thus the risks in operation are completely different.
The contaminated distance margin of 1.15 might only represent the difference between the theoretical minimum distance and the distance which line pilots can achieve on a regular basis, i.e. there is no distance safety factor.

[Bamboid]

Thanks for the replies, I agree with 100above's interpretation that since 3mm exactly, is less than '>3mm' then for pure definition purposes 3mm can be regarded as wet.

One of the reasons for my query, was that the first column of my airline's contaminated performance figures, contains data for..... 3mm of contaminant!

[noblues]

I was taxiing out in Madrass/Chenai a few months ago during the monsoon in torrential rain - I ask the Tower whats the runway state - They said 'wet'!
We could hardly taxy with the wippers on full blast ...

I delayed take-off!

It also brings another subject up in the recent UK and European WX of ATC reporting the braking action as 'unreliable' in the recent snow conditions.

I have heard this is becuase they cant accuratley measure braking action on snow - But who would land off a such a report?

[Sir George Cayley]

In the UK the only contaminated runway condition that can be measured for grip and reported is compacted snow or ice. Thats why you have snow and ice tables in the cockpit.

UK aerodromes always shut for runway sweeping and reopen once blacktop is achieved. There might be remnants of some slushy snow in traces but it's this condition for which the UK do not permit the use of the friction cart.

Sir George Cayley

[A-3TWENTY]

Hi ,

I understand that when they say the runway is wet , it means that you have less than 3 mm of water over the runway , otherwise it is contaminated.

However , I`ve got ATIS with brake actions medium, medium/poor, poor and unreliable which clearly means that the runway is contaminated , but I`ve never heard "Contaminated Runway" as we use to hear "Wet Runway".

So everytime I have a brake action less than medium , I consider it contaminated.

Am I correct? What do you guys think about?

A-3TWENTY

[FullWings]

I think you have to separate the legal (can I take off/land in the required distance in the reported conditions) from the practical, i.e. would I like to have a decent chance of staying on the runway?

Having had an 'interesting' experience with contamination early on in my flying career, I treat any sort of standing water/slush/snow/ice with a lot of respect and have a deep distrust of observations pertaining to it, especially when precipitation is ongoing.

The takeoff case is the easier one, IMHO, in that a) the aircraft is configured for maximum performance: power, flap, etc. b) the runway you have in front of you is the same length you used for your figures c) the highest risk comes from a RTO near V1: a rare event - at any other time the margins are much greater and d) you have a chance to watch other aircraft taking off and to assess the conditions as you taxi out.

Landing, I would say "all bets are off", unless you've got a decent length of runway to play with (2,500m+) as there are just too many variables. The actual touchdown point is subject to some uncertainty, even with the best technique; the braking action & wind reports may or may not be relevant for the time and place you choose to land; any delay in achieving reverse and/or speedbrake deployment can be critical; the state of your aeroplane in terms of tyre tread depth, etc. makes a big difference and, unlike the takeoff case, you don't need a failure to occur to be in the high risk zone: this is where you are every time you land on a contaminated runway of moderate length... As an aside, I think this is why we're having a rash of runway excursions/overruns at the moment as the exposure is large in this extended period of wintry weather.

[noblues]

In the UK the only contaminated runway condition that can be measured for grip and reported is compacted snow or ice. Thats why you have snow and ice tables in the cockpit.

I have always taken the snow/ice eqv. depth tables purley for use on take-off perf. calculation. And only to calculate if the eqv. depth of contaminate exceeds our landing maximum (25mm dry snow).

For landing we only have the Boeing generic landing data tables, which give distances for good/medium/poor braking actions, although we do have conventional landing data tables for wet runways, which from my perspective are usless with braking actions less than good.

If I was quoted 'braking action unreliable' on finals - I would divert.

Why risk it? Its your neck and licence on the line.

A lawyer will rip you apart when you run off the runway saying how did you know the braking action was not poor?

[Denti]

So everytime I have a brake action less than medium , I consider it contaminated.

Not allways true. Contaminated and reduced braking action are two different things, you can have reduced braking action without any reportable contamination, and not so bad braking action with heavy contamination. In fact acceleration is the main take off consideration on contaminated runways vs. braking on reduced braking action. That is why you have to check both performance charts for contaminated winter ops and take the more conservative one (well, at least we have to).

Apart from that, we do have a boeing landing distance table that gives landing distance for dry, wet, braking coefficients and reported braking action. All factored of course (dispatch info) with corrections for wind and slope, those have to be used inflight too.

[4PON4PIN]

Airbus FCOM 2 Section 4 used to define Contaminated as a runway with
>3mm of standing water, slush etc. Then a few years ago (3'ish) an amendment came out with the insertion of the word "or"

Thus: Contaminated being a runway with or > 3mm of standing water, slush...

As has been stated previously, with marginal conditions, I would suggest good airmanship would always assume the more limiting condition.

Howazabout taking off on r/w 36 with reported w/v 260-280/5kts? Zilch w/c, or a tad of tail?:)