Runway state decodes - these weren't in the book..

[Wee Weasley Welshman]

Going to Copenhagen yesterday I was confronted with the following Met info that I was unable to find a decode for (the bold numbers only)

04590259 54590266 12520175

I highly suspect that its a measurement of friction and obviously related to start, middle and end. However, the Aerad book nor the Jepp manuals offered a decode that made sense.

At the risk of highlighting my undoubted ignorance - can anyone enlighten me?

Cheers

WWW

[witchdoctor]

Hi WWW,

You're right in your assumption. The 7th and 8th digits in the runway state group refer to braking action or friction co-efficients. The numbers 91 to 95 would be used to represent braking action from poor to good, with 99 being used to indicate that there is no reliable figure. Other numbers used in the report (such as you have seen) would be to give the actual friction co-efficient; i.e, 59 = friction co-efficient 0.59.

If you want a reference source to look it all up, according to the guff I still have in my ATPL met notes it is in the UK AIP GEN 3-5-10 Meteorological Codes. That was Dec 99, so might be a little out of date now.

Interesting difference in the snow coverage between 04L and R and rwy 12. Had 12 been partially cleared or something?:8

[Wee Weasley Welshman]

Right - assumed that they would be the actual coefficients. Is there a pilot friendly clarification such as 01 - 35 Poor, 35 - 60 Medium, 61 - 80 Good?

Am obviously familiar with the 91 - 95 classifications. Telling me the actual friction coefficient is 66 leaves me somewhat nonplussed.

Cheers for the AIP Gen - I'll look it up when I next get hold of one.

WWW

[FlightDetent]

Hi 3Ws,

you're incorrect in your assumptions. ;) That is to say, you are very close to being correct. :ok:

The three number-groups are a standard though non-compulsory parts of any METAR. Called RUNWAY STATE MESSAGEs, promulgated by ICAO Annex 3 since 1998 guess I if my memory serves me still.

Your example concerns SIX runways at CPH, that is THREE pieces of concrete, namely RWYs 04L/22R, RWYs 04R/22L and RWYs 12/30. You will find further details yourself indeed, I can post if you wish.

For the sake of completness, the last two digits talk about the BRAKING COEFFICIENT (BC), being 0.59, 0,66, and 0,75 respectively for every and each piece of concrete. Please be advised, that on long runways such as at CPH, BC is measured by skidometer on three parts of the concrete-piece. RWY state message contains the lowest (=worst, most skidish) coefficient.

The BC is more elaborate version of Braking Action (BA). The break-down in such:

BA BC
5-good 0.40 and more
4-good/medium 0.36 to 0,39
3-medium 0.30 to 0.35
2-medium/poor 0.26 to 0.29
1-poor below 0.25

So in your case, the RWY state message gives you BC better or equal to 0.59, 0.66, 0.75 and that is BA better than GOOD. Good for you.:cool:

The benefit is such that my employer (JAR-OPS1) prohibits landing on runways that are BA - POOR, but in case BC is reported, we can go as slippery as BC 0.20. Same logic but different numbers apply for TKOF. All cases provided that necessary aircraft performance limitations are met.

[AhhhVC813]

Friction Coefficients: Good, equal or greater than 0.4
Good/Medium, 0.39 to 0.36
Medium, 0.35 to 0.3
Medium/Poor, 0.29 to 0.26
Poor, equal or less than 0.25

Any help?

[Wee Weasley Welshman]

Thanks one and all. An AIS relevant print out is headed to my flight bag as we speak.

Cheers

WWW

[witchdoctor]

Blimey, seems those bloody OAT groundschool notes were some use after all.:O

[LYKA]

Whilst were on the subject of runway states, can any body help with this?

I am looking for the limitations of the various measureing vehicles. e.g. limitations of the skiddometer H + L, SFH, GRT, JBD TAP etc.

Also how does one find out which airports use which (apart from in the snowtam)

cheers :confused:

[alf5071h]

LYKA, You should find an introduction to what you are requesting in a presentation given to an IATA working group:-
“Joint Winter Runway Friction Program; Aircraft Test Results.ppt” IATA APWG Briefing, September 2002 , John Croll NRC Research Officer
I cannot immediately find a web link, probably due to the file size – 7.3 mb, but an introduction to the program and the associated use of the Canadian CRFI is at: Joint Winter Runway Program. (http://www.tc.gc.ca/CivilAviation/Aerodrome/Technical/Winter/JointWinterRunway.htm)

Other info at: Friction Devices (www.tc.gc.ca/CivilAviation/Aerodrome/Technical/Winter/frictionDevices.htm)

Runway Friction Monitoring Program (www.tc.gc.ca/CivilAviation/Aerodrome/Technical/Pavement/evaluation/skid.htm)

For airport facilities and equipment see here:
Winter Services Yearbook (http://www.aci-europe.org/upload/Winter%20yearbook%202003.pdf)

Additional information, but the links are down / broken: www.eraa.org/presentations/BrakingActionMeasurementbyAlsitairScottHeadofFlightSafetyBAE Systems.pdf
One of the conclusions from this paper was: “There is no overall accepted certification to operational correlation between mu meters and airplanes”.

www.pti.psu.edu/pdfs/Pubs/9697Pubs.pdf WINTER RUNWAY FRICTION MEASUREMENT
One of the conclusions from this paper was:
“There is a considerable degree of confusion and misunderstanding within the U.S. aviation industry as to the importance of friction measurements and how they should be taken, reported, and used. In spite of FAA's identification of approved equipment and publication of methodologies for taking and reporting friction values during winter operations, most airports do not substantively adhere to this guidance. Subjective braking action reports generated by pilots and drivers of airport vehicles, which are commonly relied on in the United States, have no proven correlation to aircraft braking performance. Reliance on these subjective braking action reports may actually be a detriment to safety in some cases”.

Other references:
Report: NASA-99-tm209142.pdf
NPA 25G- 334 At JAA for final approval
Thomas Yager; Aircraft and Ground Vehicle Winter Runway Friction Assessment: NASA /TM- 1999- 209142
Jim Martin; Transport Canada presentation to IATA: Aircraft Takeoff Performance on Contaminated runways;
ASFT - History of Runway Friction Measurement. www.asft.se/ history. html
ICAO Annex 14, Operational Friction measurements
Try searching Google with ‘Joint Winter Runway Friction Program’

[LYKA]

alf5071h

Thanks very much for your links and help. Much appreciated.

Just one more qu.

As you say, the conclusion of the reports are that there isnt a good device that gives accurate and reliable measurements (wet snow in paticular)

So with that in mind does anybody have any reason why (taking the liability aspect out of the equation) British airports seem to have a policy of closing the airport as soon as it snows i.e less than 3mm (slight exaggeration) where as the scandiavian ones although with the same conditions place the decsion with the more with crew?
Is this an airport operators thing? i.e BAA etc.

[Ready]

WWW,

The friction co-efficient is denoted by 2 digits or, if the co-efficient is not available, the braking action is denoted by 2 digits.

a) Friction co-efficient, example:
28 - friction co-efficient 0.28

or

b) Braking Action, example:
95 = Good
94 = Medium / Good
and so on.......

Reference: Jeppesen Text Book, section METEOROLOGY, pages 71 & 72. I always keep a copy of those 2 pages handy in the flight bag just in case.

I hope that helped.

Happy slippery landings!!!

[Wee Weasley Welshman]

Couldn't find them in Jepp Txt Met section - will look again at specific pages as was in a slight hurry.

Cheers

WWW

[cheer up]

WWW - was your 'easy winter brief 2003' of no use - I've been to CPH many times and always have the little orange book in the map pocket.:O

[Wee Weasley Welshman]

Ahh, now you mention it that was in my flightbag but I forgot clean about it.

Cheers

WWW

[OverRun]

Alf5071h gave lots of good references and also wrote:
Additional information, but the links are down / broken: www.eraa.org/presentations/ Braking...yBAESystems.pdf
It can be found in the bit on friction at:
http://www.geocities.com/profemery/aviation.html
.