Metar decoding - doubt

[Airgus]

in the following metar from the cold Munich.
EDDM 220850Z 28018KT 9999 FEW022 SCT028 BKN250 M01/M05 Q1001 R26R/290149 R26L/290148 NOSIG

The thing that calls my attention is the rwy conditions
R26R/290149 R26L/290148

I'm not wrong 2 means wet, 9 means from 51% till 100 % coverage, 01 means depth 01 mm but 48 and 49 I can not deduct that, any help would be appreciated...

Thanks

[epsum]

I'll guess that those last numbers will give rwy friction coefficent/braking action:
RRRRERCReReRBRBR

riction coefficient or braking action


* 01…90: Friction coefficient times 100. For example, 37 indicates a friction coefficient of 0.37.

* 91: Poor braking action

* 92: Poor/medium braking action

* 93: Medium braking action

* 94: Medium/good braking action

* 95: Good braking action

* 99: Unreliable measurement

* //: Not given

[Airgus]

so in this case means the Coefficient of braking is 48% & 49%?


Thanks for the reply

[BOAC]

Always confusion here, Airgus, but there are unfortunately a few 'friction measurement systems' in use, and I believe the method used SHOULD be specified on the report, but rarely is. I suspect they are using the 'measured or calculated coefficient' table and 49 would be 'good', based on that actual given. You will see this table here. NB if the action is estimated it will be a single digit.

Where it all starts to get VERY interesting is when slippery time' arrives and you finish up having to make an intelligent guess which system has been used.

You will get a sense of the confusion here too

[chuks]

We are from the Government and...

We are here to help you. No, really!

If you go to the U.S. NOAA website, Aviation Weather Center (aviationweather.gov) and call up a METAR you have the option of getting it either in raw format or translated.

I sometimes get something that doesn't make sense to me, when I just jump back to the request page and switch to the translated METAR to see exactly what the raw format report means.

[Henry VIII]

The reported metar is not in the std 8 figures group display

R26R/290149

The US website is nice, but metar translations do not include 8 figures code :

METAR text: ESSA 221720Z 34009KT 9999 SCT006 M02/M03 Q0993 01720156 51720136 08720137 TEMPO 3000 -SHSN BKN008
Conditions at: ESSA (STOCKHOLM/ARLAND, SE) observed 1720 UTC 22 November 2008
Temperature: -2.0°C (28°F)
Dewpoint: -3.0°C (27°F) [RH = 93%]
Pressure (altimeter): 29.32 inches Hg (993.0 mb)
Winds: from the NNW (340 degrees) at 10 MPH (9 knots; 4.7 m/s) Visibility: 6 or more miles (10+ km)
Ceiling: at least 12,000 feet AGL
Clouds: scattered clouds at 600 feet AGL
Weather: no significant weather observed at this time

[chuks]

Drat.

Here in Algeria we don't have to worry about runway friction. Just as well, then.

[oz in dxb]

The 48 and 49 you are talking about Airgus is the depth of deposit from a snowtam. These figures relate to the depth of the contaminant.

48mm/49mm. Those figures go up to a value of 90, then 92 equates to 100mm, 93 150mm all the way up to 98 which is 400mm.

99 means that the R/W is not operational because of the depth of the contaminate or R/W clearance is in progress.

Oz

[145qrh]

The depth is in this case 01. The others are correct about the last 2 digits being braking coefficient.

That being said with EK we no longer use these figures to determine crosswind limits or take-off performance as they are said to be an unreliable way of judging performance degradation...

[BOAC]

99 means that the R/W is not operational because of the depth of the contaminate or R/W clearance is in progress.

- in the northern hemipshere, Oz, we close the runway BEFORE we get to 40cm of snow. Not a problem, I guess, in Dubai?

[Airgus]

thanks for the replies...

When I first saw it I thought (the same way as OZ DXB) that the snow will be up to 48 & 49 mm (0149) from 01mm up to 49mm.
But in the decoding tables I researched, I could not find 49 as a possible answer/number for the upper limit of snow rwy coverage.

tt Depth of deposit

00 = <1mm

01 = 1mm etc

thru’ to

90 = 90mm

91 = not used

92 = 10cm

93 = 15cm

94 = 20cm

95 = 25cm

96 = 30cm

97 = 35cm

98 = 40cm or more

99 = Runways non operational due snow or clearance

// = Not measurable or not significant

--------------------------------------------------

so it has to be friction coefficient:

BB Friction coefficient / Braking action

28 = Friction coefficient 28%

35 = Friction coefficient 35%
or

91 = Braking action poor

92 = Braking action med/poor

93 = Braking action medium

94 = Braking action med/good

95 = Braking action good

99 = Figures unreliable

// = not reported e.g. runway closed

-----------------------------------------------
My common sense would react as, "if I see a coefficient of friction of 0.49 (almost half) the the distances (TO and Landing) should be doubled.... well it is not like that... (I thought that my girlfriend was difficult to understand!) I guess I will have to review my atpl books about the coefficient of friction....

I have just looked at the Operational Procedures JAA book and I found another table....
In this case, a coefficient of friction of 0.49 means braking action is good,
> 0.40 is good. (or code 5)
0.39 - 0.36 is medium good (or code 4)
0.35 - 0.30 is medium (or code 3)
0.29 - 0.26 is medium poor (or code 2)
0.25 and below... is poor (or code 1)
reading unreliable (-) or (9)...

and the winner is: COEFFICIENT OF FRICTION!!

Now, due to my lack of experience in cold operations, I would appreciate if someone shares his/her own experience operating in contaminated runways.
Like how would you react on a poor coefficient of friction? company procedures, etc...

Thanks again...

Cheers,

AirGus.-

[BOAC]

I have just looked at the Operational Procedures JAA book and I found another table....

- you could, of course, have read post #4..................

Like how would you react on a poor coefficient of friction? company procedures, etc...

- you've got it! If your company does not train you, I do NOT recommend taking your contam operating procedures (or any!) from PPrune.

[Piltdown Man]

Simply put, you try not to. If the runway is long enough, you often find that you can't use it because crosswind limitation due poor braking action. The other "gotcha" that often arises is that the crews who sweep the runways not instructed to clean a width insufficient for operations. Not so long ago I was offered a swept runway with a good braking action (nice of them to test it!). Shame the width was only 15M and the swept snow was banked just beyond the cleared strip.

Generally though, if you go to somewhere like Sweden, Norway, Finland, Latvia etc. where they are used to snow, contamination isn't a problem. Their runways are swept properly and you can operate. Obviously if snow is falling or forecast, having a cast iron alternate is a "good thing" - especially one which you can use with a crosswind restriction due poor BA. In the UK though, the calendar method of flight planning is preferable. Choose a different date to fly.

PM

[Airgus]

you are right BOAC, I missed that table when I read yesterday the AOPA article... it was all there...

Regarding the company procedures, I follow your advise.

Thanks again everybody for the help.

AirGus.-

[Cecco]

Another METAR question

I recently ran into this METAR:

LSZB 300720Z VRB01KT 9000 4000NW FEW003 SCT 037 BKN 055 01/00 Q0997 NOSIG=

Now, what does the NW stand for right next to the visibility? I have a booklet with all the METAR abbreviations but I didn't find anything there. Then, it crossed my mind that NW could mean Northwest to denote the direction where the visibility observation was made (the runway in LSZB is 14/32 so that would make sense).

Any ideas?

[DB6]

If the minimum visibility in one direction is less than 50% of that in the other sectors and less than 5 km, it is included so '9000 4000NW' means 9km vis generally, minimum 4km in the NW sector. It is also included if it's less than 1500m and the 50% doesn't apply.

[BOAC]

Try this site?

Metar decode

[lion-g]

Hi guys,

Just out of curiosity, is there any rule of thumb that you guys are using regarding the coefficient of friction with respect to braking action?

For example, dry snow with coefficient of 0.50 or something along the line.

Thanks for your help.

lion-g

[TwinJock]

When it comes to snowy operations, I plead no contest - good info on this thread.

R26R/290149

I presume that the MOTNE/OPMET code was used here.

What gets me is the non-standard or seldom used codes and information added to METAR's eg. SR and SS. Took me a while to realize that this was not adverse weather!

[bookworm]

The 8-digit runway state group changed on Nov 5 along with the changes to TAF date-times. There are actually conflicting statements as to what the new format should be.

e.g. 76290149 has become either R26R/290149 (according to Annex 3, and also the consensus of METAR issuers) or R26R290149 according to WMO Manual on Codes. So:

METAR EYKA 081720Z VRB02KT 6000 OVC022 00/M04 Q1018 R08/090065=

Some states, notably the UK, Russia and Sweden, have made no change to the 8-digit code and still report in the old style.

METAR UUEE 081730Z 02004MPS 4300 -SHSN BKN006 BKN013CB 00/00 Q1008 TEMPO 0900 +SHSNRA RMK 07620337 57620337=