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GAFOR routes

Having finally experienced the exhilaration of mountain flying (well, flying high enough to stay VFR and out of trouble whilst not needing oxygen) I’m intrigued by the GAFOR routes which look both exciting and daunting. How does the O/M/D rating work? I see it changes daily, presumably based on the cloud base and the need for a higher ‘reference’ altitude. Curious to know what qualifies as ‘difficult’ as opposed to ‘marginal’ or ‘open’ – is it the amount of ducking in and out of cloud required to remain VFR? Could one not chose the highest reference altitude along a route and stick to it, or would that defeat the object of the exercise?

jgmusic
North Weald, United Kingdom

jgmusic wrote:

How does the O/M/D rating work?
Check the AIP or VFR guide…. :-)
Curious to know what qualifies as ‘difficult’ as opposed to ‘marginal’ or ‘open’ – is it the amount of ducking in and out of cloud required to remain VFR?
The O/M/D (or C/O/M/D/X even) rating is a combination of flight visibility and ceiling along the route or within the area if it is an area GAFOR.

I had a quick look in the Jeppesen VFR guide and the criteria are:

Austria/Switzerland:

O: VIS ≥ 8 km and ceiling ≥ 2000 ft
D: VIS ≥ 5 km and ceiling ≥ 1500 ft
M: VIS ≥ 2 km and ceiling ≥ 1000 ft
X: Otherwise

Croatia/France/Germany/Slovenia:

C: VIS ≥ 10 km and ceiling ≥ 5000 ft (Only used by Germany)
O: VIS ≥ 8 km and ceiling ≥ 2000 ft
D: VIS ≥ 5 km and ceiling ≥ 1000 ft (3 km VIS in Italy)
M: VIS ≥ 1.5 km and ceiling ≥ 500 ft
X: Otherwise

So the most mountainous countries (Austria/Switzerland) have slightly higher minima for D and M than the other countries.

Last Edited by Airborne_Again at 19 Jun 10:53
ESKC (Uppsala/Sundbro), Sweden

Thanks Airborne_Again – very useful to know, especially the differences between countries.

Interesting that ‘moderate’ seems to be harder, or more challenging at least, than ‘difficult’!

jgmusic
North Weald, United Kingdom

jgmusic wrote:

Interesting that ‘moderate’ seems to be harder, or more challenging at least, than ‘difficult’!

I think it means “Marginal”.

ESKC (Uppsala/Sundbro), Sweden

M = Marginal

Biggin Hill

And unless I am much mistake X = Closed

EHLE / Lelystad, Netherlands, Netherlands

Understood. An interesting distinction between marginal and difficult. I would say marginal sounds less serious – like M vs. V and I for weather synopses in SD – but I won’t argue with it!

jgmusic
North Weald, United Kingdom

Obviously, the referred ceiling is in height above ground, not AMSL.

A crucial difference to understand is that France and Germany have area forecast, I think the coding of the forecast is based on the highest altitude within the area but the weather in the majority (50+%) of the area. So do click through to the details (for Germany), and you may see stuff like “thunderstorms in less than 50% of the area” while the area is coded O (green).

By contrast, Switzerland and Austria have route forecast, where the coding refers to specific routes through specific valleys. They are valid within these valleys, within a narrow corridor. In Austria, they are based on the highest terrain within a corridor width of “approximately 3nmi” for the Austrian one.

ELLX

The ceiling height is above reference altitude, it is very important to look at those particularly in the alpine regions of Germany.

As one of the people who used to issue GAFORS this was one of the big Aha’s that I had when I actually started to do them myself. Even though for the Swiss and Austrian ones, it is a bit less difficult to understand but it took me a while to understand that e.g. the southernmost German areas 83 and 84 ḧave reference alttudes of 6500 ft AMSL. That means that even with an M the ceiling would be somewhere at 7500 ft AMSL. Also the Germans have some additional classifications which I don’t have in my memory right now, but there are things like M1 or M5 which then gives more information about the actual conditions.

The Swiss GAFORS (as do the Austrian ones) follow routes. They are issued on the basis of quite elaborate tools amongst them webcams and model calcs. Also there the difference in reference height is quite huge in the alps vs the northern middle lands. Used properly, GAFOR can yield a lot of planning information and even some climatology if seen in the past. I personally consider O and D as flyable, M and X are pretty much closed for normal pilots. An M for a helicopter however may well be flyable whereas for a 130 kt SEP it is quite dangerous to fly.

LSZH(work) LSZF (GA base), Switzerland

Airborne_Again wrote:

Croatia/France/Germany/Slovenia:

That should have been “Croatia/France/Germany/Italy/Slovenia”

Peter, if you read this feel free to edit my post above.

ESKC (Uppsala/Sundbro), Sweden
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