correction on damp runway a321

[Hoangminh90]

Recently i had a flight and we t-off on damp runway . I used the rtow chart without correction for wet . But my Captain disagreed with me that damp runway we must takd corrections for wet runway . Do you know that any ref say that because he said airbus said that 4 years ago ?

[The Guru]

H90,

I believe your captain was correct.
Airbus have published takeoff performance data for dry runways, and also for wet runways (which are runways that are covered with less than or equal to 3mm of water, slush or snow etc). Because damp runways fall within this very wide spectrum of runway conditions, the conservative approach taken by Airbus is to use wet runway performance data when calculating actual damp conditions.

The definition of DAMP, and the performance basis which should be used, are stated in FCOM>PER>TOF>CTA.

[KingAir1978]

This is an excellent document to increase your knowledge:


http://www.skybrary.aero/bookshelf/books/2263.pdf

[JABBARA]

This is the extract from FCOM (30 May 2012 for A 330) :

Note:
1. On a damp runway no performance degradation should be considered.
2. It is not recommended to take off from a runway covered with more than 4 in of dry snow or 1 in of wet snow.

However #1 is removed at new edition of FCOM. I guess Airbus did right.
Damp is not a certified runway condition therefore no info about that; however one thing is sure, "Damp is not DRY". Accepting wet calculation in Damp is at conservative side and safe.

Not current one but the place where I worked before, it was a written company procedure accepting damp as wet.

Finally, it is not a written rule but, IMHO, your Captain's discretion is right.

[FlyingStone]

CAT.POL.A.105 (d) For performance purposes, a damp runway, other than a grass runway, may be considered to be dry.

I guess it depends on the company, although most consider damp runway a dry one. The captain can obviously decide to take wet performance, just know that if donkey failes at V1 (V1wet < V1dry) your vertical margin at the end of runway might be lower (15ft instead of 35ft), despite your "more conservative" approach.

Oh, and there are many guys who preach about "more conservative approach" (wet for damp and then TOGA for wet, which is actually damp, etc.), but then follow the nice yellow line during line-up and stop the aircraft 100m into the runway. :ugh:

[Hoangminh90]

I checked on the PEF but there is only definition of Damp . I am not sure it will be degrade or not ?

[Lord Spandex Masher]

You should NOT use wet performance unless the runway is wet. Damp is not wet.

[Goldenrivett]

Hi Lord Spandex Masher,
You should NOT use wet performance unless the runway is wet. Damp is not wet.

Please see Page 64 (Appendix F) or read the whole document.
https://www.iata.org/iata/RERR-toolkit/assets/Content/Contributing%20Reports/ICAO_Circular_on_Rwy_Surface_Condition_Assessment_Measuremen t_and_Reporting.pdf

If the first third of the runway was damp, but the last two thirds were dry - then I'd agree.
If the tyres were newish, the runway was grooved or the surface drainage (surface shape, slopes) & the tire/ground interface drainage (macrotexture) & the penetration drainage (microtexture) was good (see page 16) - then I'd agree.
Otherwise, if I I thought the braking action was less than dry - then I'd use wet figures.

[FE Hoppy]

Whilst EASA officially calls a damp runway other than grass dry for perf I note that BAe recently changed their advice such that damp should be considered wet.

[Intruder]

You should NOT use wet performance unless the runway is wet. Damp is not wet.
I disagree. Unless your FCOM or other formal procedures require you to use "Dry" data, use "Wet" data (with "Good" braking action, unless otherwise reported) if "Damp" is not an option in your performance tables/computers. AFAIK, the US FAA still does not recognize or use the term "Damp" (as of SAFO 06012 re Landing Performance Assessments, still valid as of AC 91-79A of 17 Sep 14).

A damp runway is NOT dry, so you CANNOT assume that there is no degradation of braking performance. Further, you cannot dynamically assess the current status of a runway's grooving or porous surface, so you cannot be assured it retains all the characteristics for which it was designed. Further, the old 'wisdom' of accepting a wet, grooved runway as equivalent to a dry runway has been addressed and challenged in several presentations over the years (I'll try to find and post the references if nobody else chimes in). The potential degradation in braking performance for a worn, grooved or friction-enhanced-surface runway has been more recently assessed as high as 30%, which is well above previous 10% estimates AND above the 15% margin used in performance calculations.

[deptrai]

the word "damp" was introduced to confuse and frustrate people, as usually there are no corrections for it to be found. Previously a "damp" runway used to get treated as dry, more and more operators treat it as "wet". And PPrune is not an authoritative source of information, you need to deal with the ambiguity here, whatever you hear from your outfit (VN Airlines I asssume? or Jetstar or Vietjet?) should be taken more seriously. But a damp runway surely isn't dry, and while friction can be better than on a wet, it's not necessarily so. Also consider how much of the runway is damp. There's shades of gray. I can see how that question is important in a country with high humidity like VN. And wildly guessing, with some knowledge about conditions on some runways in VN - I'm making assumptions - I'll speculate your captain was not wrong, but making a decision based on a well informed guess, local knowledge, experience, FCOM and Mr A's input.

[Hoangminh90]

According to Golden rivet post . I see that we have to degrade on damp runway for dry perfomance . I will ask again maybe it í the regulation of my company ?

[deptrai]

uhm dung vay :) asking your company is a good idea.

[Togue]

Hoangminh90,
I think your Capt was right.

References:

-Definition of Damp: ( FCOM PER-TOF-CTA-20 P 1-2 10 SEP 14 )

A runway is damp when the surface is not dry, but when the water on it doesn't give a shiny appearance.


-On take off charts you have a section for wet conditions ( Influence on runway condition )

-On Runway Condition Assessment Matrix for Landing ( QRH PER-C 3-6 10 SEP 14 ) you can also find that Damp and Wet ( up to 3mm of water ) share code 5 for related landing performance. Dry runway is code 6.

[Amadis of Gaul]

uhm dung vay :) asking your company is a good idea.

Certainly better than asking an anonymous forum.

[de facto]

When runway is damp and no braking coefficient given,if your Airline/Authority doesnt provide you guidance,I would use dry perf if familiar with airport,runway condition.
If you take off from an airport with unreliable
Information and/or a runway which tends to be slippery when wet( due to for example rubber deposits,poor runway consition..)the wet perf may be a better option in most cases.

Most airports which give damp,i have found the landing distance to be very close if not exactly as dry perf..

[Goldenrivett]

Hi de facto,
Most airports which give damp,i have found the landing distance to be very close if not exactly as dry perf..
That proves nothing unless you used maximum wheel braking. A reduction in Mu (say down to wet figures) would not be apparent on a normal landing using medium autobrakes.

[Intruder]

Most airports which give damp,i have found the landing distance to be very close if not exactly as dry perf..
That is likely because of the assumptions made regarding the antiskid system when using autobrakes.

Since autobrakes target a specific deceleration rate in intermediate settings, either the autobrake regulator or the antiskid regulator will release hydraulic pressure as needed. With good braking action, the antiskid regulator will not come into play at lighter autobrake settings, so the calculated stopping distance will be the same with wet, damp, or dry. See for yourself, by selecting progressively worse braking actions, and noting at which autobrake setting the different stopping distances show up. Also note the differences for max manual braking.

It is when the braking action is medium or less, and the braking action is higher (e.g., for shorter runways or early turnoffs) that the antiskid will come into play, overriding the autobrakes and increasing the stopping distance. This could be a factor in either a short-runway landing or a rejected takeoff.

[de facto]

Interesting.
If i check dry landing distance and use intermediate AB(medium as you call it),no reverse, on a damp rumway, the landing distance will be as the dry figures....not as the wet...so as a landing issue i take damp as dry.(for planning purposes..taxiway..)
Now im getting the point above for max manual,there might be a difference,but i am not a test pilot and i wont use max braking and scare all behind:E
I do get and accept your point.
Thanks.

[safetypee]

Speculation re BAe position: damp=wet.
Apparently the UK CAA commented on the EASA draft of “4027 B. II. Draft Decision - Part- OPS - Subpart B – Section III – AMC OPS.CAT.316.A(a)(3) Performance General – Aeroplanes”, recommending that the damp alleviation be deleted; i.e. damp=wet. This recommendation was not accepted by EASA, with arguments re definition; resulting the current EASA view.

Of note there was a similar case re wet-grooved runways, where subsequently the EASA ruling was ‘clarified’ by the UKCAA, where they required depth of proof which essentially prohibits UK operators from using the EASA alleviation; FODCOM 03/2009 – interestingly titled “THE IMPORTANCE OF USING PERFORMANCE DATA APPROPRIATE TO THE EXISTING RUNWAY CONDITIONS”.

Whereas ‘wet-grooved’ is an operational issue for which the national authorities have responsibilities in implementation and safety supervision, such action for aircraft performance might not be appropriate as it would contravene internationally agreed CS25 certificated performance.
However, a manufacturer can clarify the basis of certificated performance to best represent how the data should be used; i.e. clarify any confusion between regulatory requirements, ill-defined terms, or for specific operations.

Thus a national authority and manufacturer are able to ‘politely’ disagree with EASA (regulatory two fingers) to ensure that the required level of safety, in their view, is maintained. This probably relates to historical agreements and interpretations of previous documents.
This form of disagreement is slightly disturbing as it questions the EASA process where a majority of less-well qualified (relatively new) authorities in certification matters can override a more experienced opinion. Furthermore that an operational view of performance (EU-OPS) can override a certification aspect (CS25) – normally two separate entities in EASA, i.e. a lack of joined-up thinking.

The result is that without clarification the issue resides with operators and individual crews. Irrespective of EU-OPS, Ops manuals, etc, it remains a crew’s decision at the time to judge ‘damp’, which can be questioned after an event.
For the current EASA text, the thread title might be better worded as how to determine a damp runway. And don’t quote an EASA definition or ATC report as neither will prevent an incident; only the crew can do that at the time and of course bear responsibility of any investigation finding.

Thus I choose damp=wet.
If the actual performance requires dry, find out what is the limiting factor and how might this be better mitigated as opposed to quoting some ‘get-out’ clause of a regulation.

Do any manufacturers quote damp performance? How has this been justified?

[de facto]

John ,,not everyone has an Octopus:p
Safetypee...thanks for post,very interesting reading as always.

[Intruder]

So by john_smith's operator's declarations, damp might be either wet or dry. In that case, I'd ALWAYS err toward caution! The RTO case is usually MUCH more limiting than most landings, so I don't know why they would err toward the cavalier side there.

Sounds like a political/marketing declaration (i.e., take off with more load), not a performance or safety declaration...

[Lord Spandex Masher]

Quite often RTOM can be increased by using WET Perf.

[safetypee]

??? Dry RTO distances are not based on the use of reverse thrust, but wet may be (CS25.109) ???
Overall, wet distances cannot be less than dry, but claiming wet can use different (advantageous) speeds. ??? … cue JT

[Intruder]

Quite often RTOM can be increased by using WET Perf.
If the runway is long, and the screen height is a limiting factor, that may be the case. However, if the runway is the limiting factor, I cannot see where that could be possible.

[FlightDetent]

Quite often RTOM can be increased by using WET Perf.

I was trained to believe this would be illegal.

FD (a take-off performance enthusiast)

[Anvaldra]

Do any manufacturers quote damp performance? How has this been justified?

Here is a recent AIRBUS answer to the request of my company

The European Operational regulation still states in CAT.POL.A.105 that “For performance purposes, a damp runway, other than a grass runway, may be considered to be dry.” However, the FAA Takeoff and Landing Performance Assessment Aviation Rulemaking Committee (TALPA ARC) considered that a damp runway should be considered as wet for performance assessment, both at takeoff and landing.

Airbus has changed its policy in line with the TALPA recommendation and considers that when a runway is reported as damp, performance should be calculated for wet/good braking action. You will note that in the FCOM PER-TOF-CTA 20 there no longer is a statement on the equivalence of damp with dry, instead all water-contaminated runways with a depth of less than 3mm are considered to be equivalent to wet. Furthermore, in FCOM PER-LDG-DIS-MAT, you can see that the damp runway condition is clearly associated with wet/good in the Runway Condition Assessment Matrix.

The reason for this is flight test and operational experience showing a notable braking performance reduction on runways reported to be damp. While in many cases braking action remains better than the regulatory friction curves for wet runway, there is also an issue of timely reporting by the airport of a change from damp to wet during rain showers, which makes the new policy of considering damp as wet a reasonably conservative approach.