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2 Answers

Are winds on ATIS True or Magnetic

Asked by: 20501 views , , ,
Airspace, FAA Regulations, Flight Instructor, Private Pilot, Weather

Ok the title was meant to be a leading title. So printed winds like metar and taf are true and I expected verbal winds from tower (ATIS), and AWOS to be magnetic. But tower didn't seem to know if what they read off of their dial is magnetic or true. But to create the metar, they use what they read off the dial. Which is also the same thing they record onto ATIS. I put my iPhone compass next to the dial and I swear the dial was aligned to true. It matched the variation. So....If they are reading it as true and reporting it to metar as true, then the ATIS and verbal is also true. So isn't that misleading now. "winds are 300 at 10.." woohoo, right down the runway. Oh no wait, its true. Any insight?

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2 Answers



  1. John Scarry on Feb 01, 2017

    It is surprisingly difficult to find documentation on the FAA and NOAA websites that explicitly state wind direction as either true or magnetic. Everyone knows that the wind direction in local reports, ATIS and automated weather are reported with reference to magnetic north. “Long-lines” reports, METARs, TAFs, Winds Aloft, etc. are given with reference to true north. It is probably less commonly known that wind direction for PIREPs is magnetic.

    True versus magnetic makes a lot of sense when you think about it. When you’re landing, you want to know the wind direction relative to the runway—which is magnetic. When planning flights, you don’t necessarily know the magnetic deviation of each location where you are getting wind reports, so getting the report relative to true north works best.

    When ATC (tower or enroute) gives you wind direction it will be magnetic. From Order JO 7110.65T

    l. “Course,” “bearing,” “azimuth,” “heading,” and “wind direction” information shall always be magnetic unless specifically stated otherwise.

    The instructions for creating the ATIS include this note:

    ASOS/AWOS is to be considered the primary source of wind direction, velocity, and altimeter data for weather observation purposes at those locations that are so equipped. The ASOS Operator Interface Device (OID) displays the magnetic wind as “MAG WND” in the auxiliary data location in the lower left-hand portion of the screen. Other OID displayed winds are true and are not to be used for operational purposes.

    Wind direction for the ATIS is found in the Aeronatical Information Manual (AIM)

    AIM 4−1−13. Automatic Terminal Information Service (ATIS)

    ATIS information includes the time of the latest weather sequence, ceiling, visibility, obstructions to visibility, temperature, dew point (if available), wind direction (magnetic), and velocity, altimeter, other pertinent remarks, instrument approach and runway in use.

    Also from the AIM,

    AIM 4-3-6. Use of Runways/Declared Distances

    a. Runways are identified by numbers which indicate the nearest 10-degree increment of the azimuth of the runway centerline. For example, where the magnetic azimuth is 183 degrees, the runway designation would be 18; for a magnetic azimuth of 87 degrees, the runway designation would be 9. For a magnetic azimuth ending in the number 5, such as 185, the runway designation could be either 18 or 19. Wind direction issued by the tower is also magnetic and wind velocity is in knots.

    Both controllers and pilots should use magnetic directions in their communications unless the explicitly state that they are using true.

    In “Computing Magnetic Wind Direction” http://www.nws.noaa.gov/asos/magwind.htm from .

    The National Weather Service (NWS) has received several inquiries concerning the computation of magnetic wind reports from the Automated Surface Observing System (ASOS). ASOS encodes wind reports with respect to true north in all METAR and SPECI reports, the 5-minute observations, and for use in the daily weather summary. Magnetic winds are broadcast from the Ground-To-Air (GTA) radio, appended to the 5-minute observations, and available on several video displays.

    ASOS computes the true 2-minute average wind, adds or subtracts the magnetic declination for the site, and then rounds the wind direction to the nearest 10 degrees. If the site has an east magnetic declination it is subtracted from the true direction and a west declination is added to the true direction. A way to remember this rule is: East is least (subtracted declination) and west is best (added declination).

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  2. Mark Kolber on Feb 03, 2017

    That is a very good explanation overall, but the first two paragraphs are fantastic!

    I’ve heard the adage that if it’s written it’s true; if spoken it’s magnetic. But you explanation of why that makes sense from a local vs “long lines” standpoint is really excellent.

    I guess another way of saying the same thing might be is whether the information has a “local” vs a “global” audience.

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