Slippery-Conatminated Runway

[mowk]

Hi, I was reviewing winter ops and 2 questions came up. When do we start to consider a runway slippery? (Do we consider it slippery when it is contaminated and a BA has been determined?)
What is the percentage, for a runway covered with ice, to consider it has contaminated?
I have found 2 definitions so far, one which includes any percentage of ice, an other which states that even for ice, it has to be more than 25% of coverage.
Thank's for your answers

[RYR-738-JOCKEY]

Just from the top of my head. And it's full of RYR-ops. (don't quote me on anything..) ;)
Contamination is when 25% of the rwy is covered with 3mm or more of standing water/slush. The problem with such a surface is that it reduces your acceleration on T/O and you may experience water planing especially on landing. In addition it increases your stopping distance.
Slippery runway, is usually an ice- or compacted snow-covered rwy, partly or fully. It can also be just a wet rwy (BRS springs to mind) if the rwy is not grooved. Slippery rwys will increase your stopping distance.

So, you need to check any snowtam's (or motne)+atis for rwy state to know weither it's cont or slippery. If you go to Scandinavia in winter you'll find lots of ice covered rwys..if you don't find/hear anything about cont or braking action (or if BA is reported as good) then it is to be considered wet.

Winter ops is complicated. I come from a Nordic country and from my own experience rule number one should be to know where to find the info on rwy state, and then try to establish a perception of it. That'll get you safe up and down. (BTW I grew up driving cars sideways through turns...so there's an upside to it too) :E

[oldebloke]

Just a hint BUT there is no Certification reference to Slippery runways.
I know it's a state of conditions at the time but it is only recognized as a 'poor/nil'coefficient of friction...Nobody operates off/on slippery runways,and I don't think ops manuals would say so.
Having said that,keep in mind that your friction tables should show that once
you've reached 'fair /poor'nobody knows how much concrete you will utilize
either on the 'abort takeoff or landing'..
Keep this in mind when filling out reports!!
If your the first for the landing'in situ'query ATC as to where the last traffic
stopped on the runway..Remember for takeoff Mr B'says that on a wet runway
-your brakes are only 50% effective..
cheers:ok:
PS;in the above conditions your crosswind limit is 5knots(landing)

[RYR-738-JOCKEY]

Perhaps you use another definition. But on this side of the pond:
Slippery is when BA is less than good, and there are indeed tables for it. T/O and LDG. A slippery rwy with BA poor, is another matter. We are not allowed to operate on poor.

[Ashling]

Perf section of Boeings QRH treats all runways that are wet or worse as slippery. The split is then done on braking action, good, medium or poor. A wet runway counts as good.

Contaminated state will then go by type,depth and extent of contaminant and dictate which perf rules to use

[mowk]

Thank you all for your answers.
The other day, we departed from a runway, which state was:
"10% ice, BA Good".
We considered it not contaminated nor slippery, which was confirmed when we lined up.
I just realised that I didn't know when to start considering it as slippery.
If we have, let say 30% of ice, the BA will worsen and it will become obvious to consider it slippery.
Sometime, we know a definition and we realise later that there something missing in the understanding of it.

[alf5071h]

The problem here is the lack of cohesion between regulatory definitions (both certification and operational) and any meaningful description (understanding) of what the state of the runway is and how that relates to the distance required to stop the aircraft.
A further serious problem is in communicating what relevant information there might be about the runway state – problems of words, language, and often culture.

Several threads have focused on these problems, perhaps overlooking that the regulators so far have been unable to provide a solution improves the current situation. What little information we have is technically complex and open to different interpretations. Therefore operators require considerable knowledge, risk awareness, and good judgment when landing in less than ideal conditions.

We should remember that the boundaries of the descriptions of the runway physical condition are not precise. Any runway that is wet is less than ideal; who measures 3mm of water or 25% coverage, and how are such conditions actually reported? Note that ICAO ‘Medium’ conditions may be described thus – “Aircraft are likely to use all the “wet” scheduled distance including the safety factor part of the distance, and may run even further. Directional control might be impaired”; and the description for ‘Poor’ – “Aircraft can expect to run for up to the full “very wet” or aquaplaning distance where this too is scheduled. Directional control will also be poor.” - Who schedules aquaplaning distance, and what is very wet?

The best practical advice I have found is in UK AICs
AIC 14/06 “Landing performance of large transport aeroplanes.”
AIC 15/06 “Risks and factors associated with operations on runways affected by snow, slush or water.”

“When do you consider a runway to be slippery” – ‘slippery’ is not an official descriptor or reporting term.
The consideration (the thinking process) should start with the landing briefing – there is no specific changeover point, just a continuous process reviewing the conditions. Remember, even the ICAO definitions are relative – ‘Good’ is relative to a wet runway or snow; this might assume that the crew has already taken some precautions. The conditions to consider are not just the reported runway condition; obviously they involve weight, length, wind/crosswind, approach speed, and level of braking; but less obviously, runway surface material, texture, and state of repair.

We are familiar with factored landing distances which maintain a margin of safety. Although the factors change with change in runway condition, the safety margins do not necessarily change in proportion, again assumptions are made that crews will change their operation to accommodate the reduced safety margin as conditions deteriorate … … what are the conditions where max braking assumed.

Some notable extracts / quotes from related documents.
“ … the current operational dispatch factor of 1.92 for turbojet aircraft landing on wet runways at destination or alternate airports would have to be increased to a value of 2.2 to 2.4 in order to achieve the same level of safety as that which is currently accepted for dry runway operations.” (Transport Canada - TDC - TP 14273E)

“Hence it is not practicable at the present time to determine aeroplane performance on the basis of an internationally accepted friction index measured by ground friction devices.” (EASA / JAR OPS NPA 14)

Attempts to land on heavily contaminated runways involve considerable risk and should be avoided whenever possible. If the destination aerodrome is subject to such conditions, departure should be delayed until conditions improve or an alternate used. It follows that advice in the Flight Manual or Operations Manual concerning landing weights and techniques on very slippery or heavily contaminated runways is there to enable the Commander to make a decision at despatch and, when airborne, as to his best course of action. (AIC 15/06)

The consideration should not be to determine the point of being ‘slippery’ – … 'can I complete this landing', instead it ought to be “should I be considering this landing at all.”

[A-3TWENTY]

Until what state do you consider safe for landing? Since I just have small experience in contaminated rwy`s , I consider MEDIUM a maximum to go for it .

Am I right?

Thanks

[Ashling]

If you mean Medium as a measured braking action by say a mu-meter I'd advise caution. They can be pretty unreliable and the correlation between their readings and the behaviour of a heavy jet at speed can be poor. They form only part of the picture and to base a landing on this info alone while ignoring other cues would be unwise. For this reason a-lot of airfields refuse to give out braking actions and simply say braking action unreliable.

That said my company publish a minimum acceptable braking action for take-off and landing. They do however strongly advise using the depth,type and extent of contaminate to establish the applicable performance rules and provide a table to do so. We then apply those rules when working out landing distance required remembering that Boeing only factor them by 1.15 so most add about 1.5 or so as an operating margin. I would imagine your operator would provide similar guidance or at least should.

Pireps are very usefull but take into account what the aircraft is and its weight/speed on touchdown. There will be a marked performance difference between a light and heavy aircraft of the same type.

At the end of the day if its within company limits and you've checked there is enough runway to stop for the prevailing conditions then fine but if its in any way marginal and you have another option, holding or diverting, then my advice would be to exercise it.

[tribo]

Wet RWY
Se page 6 to 8 at:
www.isasi.org/docs/FORUM_2006_01-03.pdf
Contaminated RWY
Choose Rink or Runway at:
http://www.alpa.org/DesktopModules/ALPA_Documents/ALPA_DocumentsView.aspx?itemid=6580&ModuleId=1316&Tabid=256

[oldebloke]

Alf5061h,I'm having trouble finding your TP 14273 reference.I like it ,but can't put a finger on ot.The Canadian AIM is TP 14371E and I can't say I've seen these numbers there.Has your document a title?
Many Thanks
Cheers.:ok:

[tribo]

The report can be downloded as a PDF from this link
http://www.tc.gc.ca/tdc/summary/14200/14273e.htm

[alf5071h]

Ashling “Mu meters … only part of the picture and to base a landing on this info alone while ignoring other cues would be unwise”. I agree, but beware over reliance on depth/type of contaminant as there are several assumptions in the landing data based on these measurements – not at least use of full reverse, on-speed at threshold, no long landings / tailwind etc.

ALPA (and the FAA) should be congratulated for attending to the subject, albeit several years after concerns were raised by interested parties.
The ALPA article, based on the Aug 06 workshop, identifies with many of the operational difficulties in this subject, particularly with definitions and PIREPS.
Proposals defining various levels of braking action use ‘deceleration’; however, this is subject to personal bias (body sense) and IIRC the absolute value varies with ground speed. In a sense you are using someone else’s butt to save your butt.

An alternative could be to use landing distance; this and other information is in the History of ICAO ice snow table (www.airports.unina.it/WP%20061%20Appendix%203.pdf) (via Tribo); however, this too is not perfect.

The use of PIREPS requires great care; there are many dependencies, aircraft type, wt, and crew behavior are just a small sample of the variables. PIREPS are a source of peer pressure and should be avoided as mainstream information.

Transport Canada (www.tc.gc.ca/tdc/publication/tp13361e/13361e.htm) link to the Joint Winter Runway Friction Measurement Program; for other documents see references.

Also see CRFI (www.tc.gc.ca/CivilAviation/publications/tp14371/GEN/menu.htm) AIR 1-11.