I understand that METARs report wind direction as true and ATIS reports it as magnetic. But at Camarillo (KCMA) both are reporting the same wind direction and speed even though the magnetic variation is 12.5 degrees. Why does the written versus spoken rule not apply here?
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2$\begingroup$ Are you comparing reports recorded at the same time? $\endgroup$– minsCommented Nov 6, 2016 at 1:13
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1$\begingroup$ Related: aviation.stackexchange.com/questions/60/… and aviation.stackexchange.com/questions/29643/… $\endgroup$– 60levelchangeCommented Nov 6, 2016 at 7:53
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$\begingroup$ Written vs. spoken rule is not a rule, at least not that I can find tracable to any official source. See AC 00-45G. $\endgroup$– 2NinerRomeoCommented Apr 4, 2017 at 19:34
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2 Answers
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For the US
From the FAA ATC manual:
2−9−3. CONTENT
NOTE− [...] 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.
Which confirms the ATIS winds are magnetic.
I just listened to KCMA ATIS, the wind reported is 10 degrees more than the METAR.
Make sure you match the ATIS and METAR times. On liveatc.net they were not the same, I had to check the METAR from aviationweather.gov to get the correct reporting time.
For Europe
It's not the same.
Both METAR and ATIS report mean wind information, for the direction, both report in true heading. ATC report is magnetic.
ATIS wind velocity is latest two minute average. The wind direction broadcast is given in degrees true.
[...]
ATC plain language ad hoc wind directions given during final approach or just prior to or during the take off roll are likely to be given in degrees magnetic.
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$\begingroup$ Your answer is not correct. In the US. METARs and TAFs use true. ATIS and tower use magnetic. $\endgroup$– JScarryCommented Nov 8, 2016 at 17:32
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1$\begingroup$ It’s puzzling to me why the ATIS in Europe would be referenced to true north and not magnetic. The compass, directional gyro and runways all use magnetic north. So when you are coming in to land, you know the wind speed relative to the runway and your track. Since most of Europe only has a few degrees of variance between true and magnetic, is that why they use true in their ATIS? $\endgroup$– JScarryCommented Nov 8, 2016 at 18:23
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Here’s the info for ASOS.
VOICE MESSAGES
ASOS computer-generated voice message are made available through telephone dial-in access and are broadcast directly to pilots via ground-to-air radio (where installed). The information contained in the ground-to-air radio broadcast message and the telephone dial-in message are identical. The voice message is composed of the body of the ASOS observation and selected remarks. Selected remarks can include variable visibility, tower visibility, or Density Altitude when 1,000 or more feet above airport elevation. Control tower personnel may add Notice to Airmen (NOTAM) or other information. Note that wind direction in the voice message is given in degrees magnetic.
