View Full Version : ATIS - Wind direction in True or Mag?


Specaircrew
5th Mar 2001, 23:31
We all know that TAFs and METARS give the surface wind in True. The aircrew in our crewroom are all under the impression that ATIS winds are supposed to be magnetic(cos that's wot we were taught and runways are in mag!) This has recently caused heated discussion with the chaps in ATC who simply copy down the true wind that's passed by the Met Office and put that out on the ATIS.

A trawl through the books finds a quote in JSP 318A (Military ATC Bible) that says that ATCOs are responsible for applying variation to the true wind supplied by the Met Office when choosing a runway direction. We've found nothing yet that explicitly states whether you should use true or mag in the ATIS.

Of course with 4 degrees variation it doesn't really matter here but most of us regularly operate into windy airfields with big variations so we'd like to clear up any confusion!

Any comments



3rd Runway
6th Mar 2001, 00:26
I think you will find that the ATIS is only a verbal rendition of the METAR. Consequently, you should treat the information with the same amount of caution as it may be the best part of an hour out of date. Remember, met 'specials' are only issued on a significant change of weather.

Lew Ton
6th Mar 2001, 00:32
Yes, our ATIS is automatically spoken from what is sent out as the METAR, which is suppose to be degrees true. However, with a variation of less than 4deg it doesn't matter much, but in some parts of the world. . . :)

no sig
6th Mar 2001, 03:49
ATIS, and correct me if I'm wrong, was supposed to relieve r/t congestion by saving the ATCO the need to relay a/d essential information, which included runway in use, wind etc. therefore the application of variation to wind was implicit, as it is when given on approach by the twr. Yep methinks it should be degrees mag. Not to bad if it's in the UK but try missing 20 odd deg VAR or so when operating out of BIKF on a windy day.

NudgingSteel
6th Mar 2001, 04:02
Not too sure about the new automated ATIS, but when it was recorded by our ATSAs, they always added a correction value to turn it into a magnetic number.

passepartout
6th Mar 2001, 06:51
When I wa trained as an assistant I was indeed told to add the variaton and round up/down to the nearest 10 before broadcasting on the ATIS.
However surely the next part of the argument is, should I be applying that variation to the wind checks I give as a tower controller?

HEATHROW DIRECTOR
6th Mar 2001, 12:12
no sig... All the bloke in the tower does is to read the anemometer dial. Whether that's mag or true I don't know, although I've always assumed it to be mag. (I never saw any adjustments applied to the equipment when I worked in Heathrow Tower). I did a spell as a met observer yonks ago and my reports simply quoted the wind off the anemometer and I assume that's the info we all get in metars so precisely "which" wind it is I don't know.

eyeinthesky
6th Mar 2001, 12:28
Logic says the anenometer in the tower should give the magnetic wind as it's useful to know when you're landing on a magnetic runway (sic). Are there any met chaps out there who want to comment about which wind they intend to put out on the ATIS?

------------------
"Take-off is optional, Landing is mandatory"

Specaircrew
6th Mar 2001, 12:33
The wind 'off the clock' in the Twr is always mag because that's the way it's calibrated(usually)and it would be pointless a controller passing a surface wind to a/c on finals in true as it would require a mental calc from the pilot.

I'm glad to see that there is a difference of opinion between what is actually done on the ATIS and what should be done. I can't seem to find any document that states whether ATIS winds should be in true or mag. From a pilots point of view I would prefer it in mag because that's the info I use for initial take off/ landing calcs and at places like Gander it makes a lot of difference.

I get the impression that in the UK, because the variation is so small, no one has really noticed that some pilots think they're getting mag on the ATIS when they're actually getting true.

Brave
6th Mar 2001, 16:02
I was taught that anything spoken was in magnetic and anything written is in true.

cossack
6th Mar 2001, 16:24
On the old Munro dials (remember them?) there was sub-scale that could be adjusted by the Met Technician for variation. The one that was in the observer's room had zero variation but the ones in ATC had the variation added.
As for our new digital kit - who knows?! But it should be magnetic!

static
6th Mar 2001, 18:47
ATIS is definetely magnetic, as tower reported winds are.
Everything you find in the met-folder is true.

Specaircrew
6th Mar 2001, 19:08
Was told by one of our ATCOs today that the civvy ATC bible states that ATIS winds should be passed as mag. This RAF station uses the true wind supplied by Met as does the RAF ATC school at Shawbury, not sure what happens at other UK bases but would assume they do the same. Not a real problem while flying in the UK but a chap could be caught out if he gets it wrong overseas.



[This message has been edited by Specaircrew (edited 06 March 2001).]

RATBOY
6th Mar 2001, 21:58
Looking at the U.S. systems ATIS is magnetic north referenced (Airman's Information Manual para 4-1-13) The automated surface observing system (ASOS) and other automated systems produc ea true north referenced output for METAR and SPECI reports, 5 minute observations and the daily wx summary. When the asos is fitted with the ground to air radio feature it converts to magnetic before broadcast. Not sure what the digital ATIS in oepration at some locations over ACARS provides.

Seems the problem might be when whoever created METARs and internationally standardized them maybe they forgot who used them. Then the automation and automated wx observing engineers just provided what was demanded at the output.

references: www. faa.gov/ATPubs/AIM
www.nws.noaa.gov/asos/magwind.htm (http://www.nws.noaa.gov/asos/magwind.htm)

Scatterling
6th Mar 2001, 23:42
I think UK military ATC should put their hands up on this one and say they have got it wrong. If they haven't known all this time that they were supposed to be converting the Metar from true to mag then they have been found SEVERELY wanting.

Correct it soon, please.

3rd Runway
6th Mar 2001, 23:47
Scatters, the problem is that us military types can only add in multiples of 3; what if the variation is a whopping 4 degs?

Specaircrew
7th Mar 2001, 01:16
Add 6 and take away 2 :-)

Bizzy
7th Mar 2001, 01:29
Scatters

1. ATC is not responsible for the info - it is the met department.

2. The info given over the radios (by ATC, standfast ATIS) is Mag, as pointed out above - the anenometers are calibrated (and are maintained by the Meteorological office - the civil service)

3. ATIS is only changed when the weather changes significantly i.e. a QFE, cloud, Vis change. Therefore the wind is a mean wind - not changed unless strength or direction changes significantly. ATIS could be the same all day.

4. Therefore - the wind on ATIS is not instantaneous and could be way out - that is why you are given the wind on finals or at the commencement of an instrument approach, and at any other time that it significantly changes. This wind is corrected.

5. Even if it was a cock up - which it is not really when you consider the facts above - why should the ATC or even Met department have noticed it? You obviously did not until the thread was started!!

Yes, I have bitten on your comment - but with just cause.

Steps off soap box

[This message has been edited by Bizzy (edited 06 March 2001).]

[This message has been edited by Bizzy (edited 07 March 2001).]

Specaircrew
7th Mar 2001, 02:58
Bizzy Old Chap/Girl,

The point is that because it is stated in UK/US docs that ATIS winds are to be in magnetic, this is what pilots expect to receive. In fact I've yet to come across an overseas airfield that broadcasts in true!

The whole reason for having an ATIS is to stop pilots having to call the Twr, if I called you from 100 miles out I wouldn't expect you to pass the wind in true!

ATC are responsible for what goes out on the ATIS so I don't think it's unreasonable to expect them to add or subtract the variation to the true wind before making the tape!

I'm afraid the old 'we just pass what the met man gives us' argument doesn't hold much water for military ATC as it clearly states in JSP 318A that ATCOs must remember to convert the wind supplied by the Met office to magnetic (surely this was taught during basic training?)

The real question being asked here is; if pilots and ATC in the rest of the world know that the ATIS wind is supposed to be magnetic why is it that some UK ATCOs don't?

The obvious answer being that 4 degrees variation makes bugger all difference, so the theory has got lost in the sands of time and we're into the 'but we've always done it this way' mentality. A shame really because one begins to wonder what else wasn't taught at ATC school :-)

[This message has been edited by Specaircrew (edited 06 March 2001).]

[This message has been edited by Specaircrew (edited 06 March 2001).]

Binary
7th Mar 2001, 14:15
For those that have confidently stated that ATIS is magnetic. ATIS broadcasts exist that are (or have been) generated automatically from a lexicographical scan of the METAR message, without any variation being applied. They are therefore in deg true. In these cases there is no human intervention in the process. Others may be different of course.

Steep Approach
7th Mar 2001, 15:57
On instaling / replacing windvane heads. They are always compass aligned, a magnetic device. The hardware does not have any special alignment mechanism so I'd say that whatever it is set to, it is never truly accurate.

Specaircrew
7th Mar 2001, 20:15
Binary,

I think the automated services you speak of insert the word 'True' after the wind direction? If not, for US airfields,it contravenes the FAA AIM Official Guide to Basic Flight Information & ATC Procedures Chapter 4 Sect 1 Para 13. I've been told that the UK equivalent CAA document is no different.

Bizzy
7th Mar 2001, 21:32
SpecAircrew

Contrary to belief, ATIS is the responsibility of the MET department, and in all but the oldest of towers, is automated.

If you were to call up 100 miles out, the wind will quite probably change in the 10-15 mins minimum it would take you to get to the overhead (unless illegally flying supersonic!) and is therefore just an indication of the trend - as per point 3 in my earlier post.

Even a change of 10 - 15 degrees would not neccesitate a change in the ATIS. Being Ex aircrew, I can find no reason to take into consideration the wind 100 miles hence to such a degree as you indicate unless my fuel planning was woefully bad.

The wind direction you are given over the radio by ATC is MAG, (not neccesarily so with ATIS), but given the paragraph above this, is there any real need for an exact wind so far out? I as this as an ex Lynx man - certainly not pointy and fast, therefore I may be missing something, though I can't think so.

As per 318A though, ATC does readout Mag wind, 'cos thats what the anenometer gives us!!

[This message has been edited by Bizzy (edited 07 March 2001).]

Specaircrew
7th Mar 2001, 23:44
Bizzy,

I think you mean the Met portion of the ATIS is the responsibility of the Met dept, all the other stuff such as taxyway closures, bird hazards, braking action etc is input by ATC. So if ATC knows that met winds are true and ATIS is supposed to be mag why can't varn be added or subtracted prior to transmission?

In reply to your other question. Let me just put forward a typical heavy jet scenario.

If the forecast wind for an airfield was close to the a/c x wind limit prior to departure, and then the ATIS wind prior to TOD is out of limits it can have a major input on your decision whether to divert or not.

For example crossing the pond in the winter it's not unknown to find yourself with a fuel state that requires a decision to be made at top of descent(100 miles out). In general wind directions don't change very quickly unless a front is going through or there's a TStorm close by, so the most recent ATIS wind is usually pretty accurate.
We know the wind off the clock is mag but to be honest an instantaneous wind readout 15 mins prior to landing can be deceptive as it could be between gusts or vica versa, what we really need is a mean and that's usually what the ATIS provides.

If a pilot cocks up his mag and true at somewhere like Gander (25 deg varn) when there's a 35k wind it can make all the difference between an illegal x wind or LDR. All fine and dandy if you're fat for fuel and can sit in the hold and chat with ATC but this is not always the case.

I hope you can see that it can be quite important that pilots shouldn't be confused as to exactly what they're getting from the ATIS. We're all trained to expect mag (because that's what it says in most international docs) so it was just a little surprising that some ATC units don't make the conversion before making the tape.

Bizzy
8th Mar 2001, 01:08
Spec

Thanks for the explanation re Heavy Jets across the pond (sincerely)

Just for interest,

At the station where I work, the only input ATC has into ATIS is runway in use - MET are informed at the beginning of the day and then told as and when it changes and they consequently input that into ATIS.
Bird formations, taxiway closure etc are not broadcast our ATIS - they are given when the Ac first calls for recovery, or via Lon Mil. - I appreciate it may be different elsewhere. (If braking action or any other serious situation arises during the day, we will ensure Ac inbound will find out before this point, by the usual methods, Guard etc)

Our Met department - in common with all other airfield met departments, should be, aware of the requirements regarding Mag wind, as per the pubs. They are responsible for producing aviation weather in the correct format!!

I fully agree with you that if ATIS is spewing out the wrong info then it should be looked into. The catalyst could be ATC or aircrew - either could easily speak to the met wizards and witches to find out exactly what they are broadcasting, and if wrong, suggest changes. I know I will certainly be speaking to the met department here tomorrow.

Flight safety and flight safety implications are everyones responsibility - if we think someone from another department is doing something wrong, we should advise. But, just to set the record straight, the Met department are wholly responsible for ensuring the correct information, in the correct format, is relayed by various media - METARS, TAFs, ATIS etc.

Scatterling
9th Mar 2001, 22:10
Spec, well done for explaining to the heathen and retaining your patience!

Bizzy, I can see that you are coming round to Specs line of thinking but I must disagree with your final line in terms of military ATC (after all, this thread was specifically about military ATC but ATIS in general).

The appropriate military document, JSP318A, clearly says that ATC are responsible for converting all true met data into magnetic. I have recently seen a civil USA doc that says, more explicitly, the same thing. I shall have to dig into the UK civvy books to see what is expected.

At least this discussion raises everyones awareness of the potential pitfalls!

LXGB
14th Mar 2001, 23:15
Hi Folks,
At the risk of sounding like a rivet spotter...
New wind dials, aka Mk 6 Airfield Wind Display System, was recently installed in most RAF towers and approach rooms. It displays the instant wind in Magnetic and thats what we give out over the RT.
A 2 minute average, 10 minute gust and 2 minute crosswind are also available. You can adjust the variation from the on-screen menu (PC based system), but we leave that to met.
The only problem is they're a swine to read up in the tower when it's sunny, but thats progress for you.

LXGB.


PS - Nothing.

smooth approach
14th Mar 2001, 23:32
LXGB

Thanks but the guys are actually talking about the DATIS which is ordinarily a verbal rendition of the METAR. Wind dials (regardless of mk) have provided magnetic information for quite a few years.

PS Spoke to an air traffiker today at my parent airfield and they apply mag variation to METAR when recording DATIS. I asked them waht the authority was; "dunno" was the answer.

Bizzy
15th Mar 2001, 01:05
LXGB

thank you for reiterating what I said about mag input from wind vanes.

Smooth Approach

At the station I work at, as an air trafficker, there is nothing anywhere, regarding ATC being responsible for ATIS - it is in the met departments TORs (a uniformed Met department - should give you an idea of the service I work for!)

As a met department responsible for airfield weather (uniformed or not) - they have publications which stipulate the format of METARS, ATIS, etc.

Yes 318A does mention mag wind should be given by ATC - but they can only do this for the information they are responsible for providing (NOT ATIS!!!)..

To summarise - if I may.

The Met department are wholly responsible for the weather, ATC provide weather info as given by said Met department. Apart from some smaller (essentially civvy) airfields, where the ATCO is a qualified met observer, ATC have no other input. The ONLY Wx factor that ATC can instantaneously give without reference to Met Dept, is wind, via the corrected dials!

I (finally), rest my pussers grip!!

smooth approach
15th Mar 2001, 01:50
Bizzy, couldn't agree more. IMO the ATIS should be a verbal rendition of the METAR combined with ATC stuff like serviceability etc. That is all. Importantly, it is an observation and is only a snapshot of the wx at a particular time. I was suprised when my stn said they converted true to mag for the DATIS b'cast, however with 4degs variation it's not worth dying about.

HEATHROW DIRECTOR
15th Mar 2001, 12:18
I've read most of this thread with interest and am concerned that some pilots really believe they're getting an ultra accurate wind from either us or the ATIS... I have to confess that in all my years in ATC I doubt if I've read out a truly accurate wind on more than a few occasions. When I was a tower controller giving landing or take off clearances I'd glance at the anemometer and give the bearing to the nearest ten degrees except under extreme conditons when I'd go down to five. Anyone who sits watching an anemometer all day will understand that it's pointless worrying about whether it's true, false, magnetic or centigrade - the needle wiggles around constantly over at least a 5 degree arc and usually more. Under certain conditions at Heathrow it used to spin through 360 degrees! I've never read a wind, for example "237 degrees at 17 knots" in my life - it would have been "240 at 20".

Who was it who said "Met is an inexact science"?

cossack
15th Mar 2001, 12:32
We now give the 2 minute average as the norm. This negates the needle-flicker that HD mentions. What is important to remember is that it is an average and so what you may experience may be slightly different, but not different enough to have had an impact on the average yet.
We can still, if requested, or if we believe it necessary, pass an instantaneous windcheck.
On a moderately blustery day, direction will vary by more than 30 degrees either side of the average. The speed has to vary by +/- 10 knots before the equipment will notify a max or min.
Unless the wind is approaching limits for an approach, then whether or not a small variation is added to the METAR for the ATIS is neither here nor there.

(typos)

[This message has been edited by cossack (edited 15 March 2001).]

matspart3
16th Mar 2001, 02:46
HD makes a good point about the 'averageness' of what is passed but shouldn't we try a more radical approach. Brize Norton has an electronic gizmo that gives a crosswind factor (undoubtedly developed at enormous taxpayer's expense)...after all isn't that what everyone is intersted in at that stage of the flight?

Specaircrew
16th Mar 2001, 03:49
Heathrow Director,

Pilots only expect the wind to be reported to the nearest 10 degrees(iaw regs) and for the speed/dirn to be a mean on the ATIS and a more accurate mean when read 'off the clock'. You're right that in the UK it doesn't make a difference if you use true instead of mag but it certainly does if you're at an airfield where the varn is 28 degrees! ICAO standard procedures are supposed to make sure that pilots are aware of exactly what sort of information to expect from ATC when operating worldwide.

It would appear that this particular subject is a bit of a grey area because despite pilot reference docs clearly stating that winds on the ATIS are to supposed be mag there doesn't seem to be anything in UK ATC rule books that say this?

Bizzy
16th Mar 2001, 17:13
SpecAircrew

Your final paragraph is correct in assumption. One would hope however that the met department had the required references, and that they did indeed require Mag on (D)ATIS.

Any Met obs around who can shed light on this? (PROB30 that there is not!)

LXGB
17th Mar 2001, 05:20
HD,
Couldn't agree more. No matter how much gucci kit we have, the "wind off the clock" is exactly that. A quick glance and it's passed.


MATS Pt 3,
As mentioned earlier in the thread, most mil towers have the same kit. The additional info is never asked for and seldom volunteered. Good point though, any aircrew comments welcome.

Stay frosty,

LXGB.

smooth approach
17th Mar 2001, 13:35
Ok, I read both the UK AIP and Mil AIP and it is somewaht vague. Interestingly, there is little said about ATIS. However, at my unit the ATIS is the METAR together with othe ATC bits. Although ATC add the mag variation, I'm not sure they should. The AIPs specifically stae that METARs give wind in 'True'. More importantly, the docs define the required accuracy and it is interesting to note that the wind speed and direction is a 10 minute average.

Best we find a met man to clarify the issue.


Smoothie

[edied for spoll chock]

[This message has been edited by smooth approach (edited 17 March 2001).]

Zarg
18th Mar 2001, 13:41
Reading this thread with interest I thought I might bore you all with the Australian perspective!

The wind quoted on the ATIS - including Digitised broadcasts - is ALWAYS given in degrees magnetic. METARS and SPECIS are issued by the Bureau of Met and wind speeds are given in degrees true with the following qualification extracted from the Manual of Air Traffic Services:-

"NOTE: In observations for take-off and landing, the wind direction is given in degrees magnetic, and in all other observations in degrees true. The information presented on the wind direction indicator installed in ATC consoles is a reading corrected to show direction in degrees magnetic. When (ATC) staff use the reading from this instrument to compile aerodrome weather reports (METARs and SPECIs) they should make the appropriate correction to give a direction in degrees true."

Bearing in mind that variation in Oz can vary from 3W in Perth to 13E in Sydney this difference can be significant.

Autralian ATCOs, civil and MIL, are qualified MET Observers and they compose the ATIS with the following guidelines with regard to present wind:-

"..the current values of meteorological information vary by or exceed the following values and are expected to remain that way for at least 15 minutes:
(1) Wind - direction 10 degrees - speed 5 knots...."

Wind direction and speed for a landing aircaft is given based on the wind analyzer - where fitted - at the landing threshold, and for departure at the upwind threshold.

Ain't we a clever mob! Hope this helps!

------------------
Be CAREFUL out there!

Ausatco
18th Mar 2001, 17:32
Thanks, Zarg. In addition to the better weather that everyone knows we have down here, I think you've surely convinced them that we have better wind too. :)

At my location there are 6 wind analysers - one at each end of each runway. The analysers indicate an instant wind, a 2 minute average and 10 minute peak winds.

We use two parallels and one crossing runway.

When devising a wind for the ATIS, we try to quote a wind that is representative of all the wind readouts at the relevant runway ends. That may involve a bracketed wind, eg 120 to 160 degrees, 10 to 15 knots, gusting 20 knots. We also quote mean and max crosswind and downwind components for the runways in use.

If one threshold or one DER wind is significantly different from the others, then we quote the representative wind from the "majority" and also advise the "different" one, with components.

We do not routinely provide wind checks to every landing or departure, on the basis that the ATIS is supposed to be reasonably accurate and comprehensive - though we do provide them on request.

I believe that changes are on the way. Much less detailed wind information will be quoted on the ATIS, but representative nonetheless, with accurate windchecks for each arrival and maybe departure with landing and TKOF clearance.

AA



[This message has been edited by Ausatco (edited 19 March 2001).]

Specaircrew
19th Mar 2001, 19:59
Smooth Approach,

You're right the UK docs are very vague on the subject. If you have a look at the FAA equivalent it clearly states that ATIS winds are to be mag. I can't remember ever receiving true winds on an ATIS at an airield with a significant varn.

This subject only came to my attention because the word 'true' started appearing on the ATIS at my home airfield, a pointless exercise because the mag wind rounded to 10 degrees is of course exactly the same with a varn of 4W!

PS Just spent the night in Rio (varn 21 deg) and the ATIS was in mag.



[This message has been edited by Specaircrew (edited 21 March 2001).]