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filipvtt



Joined: 14 Feb 2017
Posts: 2

PostPosted: Tue Feb 14, 2017 3:36 pm    Post subject: Remark "OPR SIGNIFICANT CONT F)1 G)XX H)5/5/5" Reply with quote

Hi

In some Snowtam it is written "OPR SIGNIFICANT CONT F)1 G)XX H)5/5/5"
OACI Notam decoding does not give any clue about this.
Does it mean there are several contaminants and the significant one is the one indicated?
If you have frost (1) and Ice (7), but only frost (1) significant, do you ignore Ice for take of and landing performances?

Thank you for any reply.
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K.Haroon
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Joined: 11 Dec 2005
Posts: 1292

PostPosted: Sat Feb 18, 2017 4:39 am    Post subject: Reply with quote

Hi

Quote:
In some Snowtam it is written "OPR SIGNIFICANT CONT


According to my understanding that's the caption under which details of operationally significant contamination is given e.g.

F)4 G)30 H)1/1/1 = (F)Runway covered with (4)Dry Snow, Depth (G) of contamination is 30mm, Braking Action(H) is (1)Poor.

In your case F)1 G)XX H)5/5/5" = (F)Runway (1)Damp, Depth (XX) cannot be measured, Braking Action(H) is (5)Good.

Although damp runway does not sound "significant contamination", but I assume they keep the caption constant and mention whatever the runway condition is under that caption.

Quote:
Does it mean there are several contaminants and the significant one is the one indicated? If you have frost (1) and Ice (7), but only frost (1) significant, do you ignore Ice for take of and landing performances?


The "F" field shows runway contamination (any deposits on the runway). The runway is divided into three equal parts, and the SNOWTAM will give the values for each third divided by a slash (/). The following codes are used to describe the type of contamination:

NIL: Clear and dry
1: Damp (Not Frost)
2: Wet or water patches
3: Rime (normally less than 1 mm deep)
4: Dry snow
5: Wet snow
6: Slush
7: Ice
8: Compact or rolled snow
9: Frozen ruts or ridges.

There may be more than one code used for each third of the RWY. If this is done, the codes will show the different layers of contamination from the top down e.g. F) 48/7/47. 48 thus indicates that there is dry snow on top of compact snow on the first third of the runway, the next third has ice (7), while the last third is covered with dry snow on ice (47).

You don't ignore anything.

Check this link for more on SNOWTAM http://www.theairlinepilots.com/flightplanningforairlinepilots/snowtamdecode.php
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filipvtt



Joined: 14 Feb 2017
Posts: 2

PostPosted: Sat Feb 18, 2017 4:13 pm    Post subject: Reply with quote

Sure (3) is for rime or frost, (1) for damp
But when snowtam indicates F)37 G)X/X/X H)5/5/5 it clearly means that ice is not significant and you can ignore it for TKOF/LDG performances?
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K.Haroon
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Joined: 11 Dec 2005
Posts: 1292

PostPosted: Sun Feb 19, 2017 4:47 pm    Post subject: Reply with quote

Ok I though we were talking about horizontal distribution. Your query is about vertical distribution e.g. ice on runway and some contaminant on top of ice. Though I haven't come across performance in FCOMs that cover this situation, but I think in some cases it will be hard to ignore the bottom layer if the depth of contaminant above is very shallow like e.g. only 1mm of dry snow on an icy runway as compared to 1mm of dry snow on a non icy runway. I assume performance should be different in both cases.
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