A question that I've never seen answered satisfactorily.
Magnetic makes sense, because runways are based on magnetic and you should reduce the workload of pilots whenever possible.
I have never seen anything written down. I just had a flick through ICAO Annex 11 for good measure, and it doesn't say anything either.
What is interesting is that the people "doing" the ATIS aren't always in agreement. Responses include:
(more recent, not so helpful) "I read it off the computer screen, I don't know if that is magnetic or true"
(older but more helpful) "We used to make a variation correction before broadcasting"
(implying it is true) "It is a direct copy of the METAR"
So the summary is:
I don't know what the correct answer is; and
Even if there is a correct answer, not everyone will be following it!
NATS teach trainee ATCOs the following (This is a powerpoint slide from Basic training):
How wind is reported
Met forecasts and observations - degrees True
Passing observations to aircraft (including ATIS) - degrees Magnetic
So paddywak, you're quite right. What you hear over the radio should be degrees Magnetic. What you read in METAR/TAF will be degrees True.
Tom also has an interesting point about accuracy - remember METARs will be telling you a 10 minute average anyway; while I don't have anything written down, wind is generally directionally described in 10 degree blocks, isn't it? Any equipment I've seen, tends to be a marker on a compass rose, rather than a directional figure - so it'd be down to the meteorological observer to be as accurate as possible.
And finally, I'll leave you with this, also from a NATS presentation slide on the subject.
Passing wind is one of the most important duties of an ATCO
Further to the above, from the Manual of Air Traffic Services (MATS) Part 1 (CAP493)
9.6 Information to Aircraft
After an arriving aircraft has placed itself under the control of Approach Control, the
following information shall be passed as soon as practicable:
a) Runway in use;
b) Current meteorological information together with the time of observation:
i) Surface wind direction (in degrees magnetic) and speed. The maximum wind
speed should be included if it is 10 knots or more greater than the mean speed
and the extremes in direction when the variation is 60 degrees or more and the
mean speed exceeds 3 knots.
Controllers should note that anemometers indicate magnetic direction but
meteorological reports give wind direction in degrees true;
10 Transmission of Meteorological Information
10.1 When controllers receive requests for meteorological information from pilots they
must ensure that the information supplied conforms to the request, e.g. a report
should not be given in place of a forecast.
10.2 As a general rule, controllers shall only transmit meteorological information that has
been supplied, or agreed, by the Meteorological Office. The exceptions are:
a) Indicated wind direction (degrees magnetic)
11.7 The ATIS message should contain all or part of the following elements of information
in the order listed:
• Surface wind direction (in degrees magnetic) and speed, including significant
Joined: Mar 29, 2006 Posts: 289 Location: Scotland
Posted: Sun Feb 19, 2012 9:07 am Post subject:
another spanner in te works of course....
Off-shore, the radio op will pass you the wind in true, cause they ARE just reading it off a screen. _________________ Generally wrapped in rubber, be it in the air or on the water.
If they hold an ATCO licence, then we've an issue here. Quite clearly, MATS states magnetic. That's the only permissible way to transmit a wind direction via RT. (I would hope ATSAs that provide similar services adhere to that rule too)
If they're reading it off the screen, perhaps there should be a consideration to the 'screen' providing a magnetic correction.
If they're not ATCO/ATSAs, but operations staff, I don't see what you can do about it really! _________________ J.
Last edited by James T Lowe on Mon Feb 20, 2012 8:59 pm; edited 1 time in total
Not sure if ICAO is the primary source - I imagine ICAO was used as a starting point, but MATS has evolved a bit over time to how UK ATC operates.
1.1 Air Traffic Services within the UK are provided in accordance with the Air Navigation
Order and Rules of the Air Regulations. Generally these are in line with the Standards
and Recommended Practices of the International Civil Aviation Organisation.
If you're interested, in the Foreword of MATS1, is the following:
Operational controllers are expected to have a detailed knowledge of Sections 1 and
5, together with the same degree of knowledge of those Sections appropriate to their
Which you can take to mean that all the licensed operational controllers will have learnt most (if not all) of those sections, verbatim. Yes, absolutely word for word. I can't vouch for how much they might remember, but 4 years on, I reckon I still remember a surprising (if a little scary) amount of it! _________________ J.
Joined: Feb 14, 2008 Posts: 888 Location: Stavanger, Norway
Posted: Tue Feb 21, 2012 8:24 pm Post subject:
Helideck headings offshore are noted in both true and magnetic unlike runways. The difference in the North Sea is going to be less than 5-10 degrees depending if you east or west of the median line, not worth worrying about to be honest.
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