Quite honestly, it wasn’t until years after becoming a pilot that I even thought to ask this question. The only time that true vs. magnetic heading was really emphasized during training was in my cross-country calculations, where I had to always factor in a magnetic variation. Because of this, I assumed all winds might be represented as a true heading. It turns out that’s actually not always the case. So, are winds reported in true or magnetic headings?
Winds shown on a METAR, TAF, winds aloft table, or surface analysis chart are represented in true headings, whereas winds represented through an ATIS, AWOS/ASOS, or PIREP are in magnetic headings. A useful adage is that “If you read it, it must be true. If you hear it, it’s magnetic.”
While catch phrases can be helpful, it can be more helpful to memorize the “why” behind winds being reported in true or magnetic headings. There are some important reasons that they are reported differently, so let’s go through some different examples of each to determine the reasoning.
Are winds reported in true or magnetic headings?
Winds are reported in both true and magnetic headings depending on where the information is being presented. At first glance this can sound frustrating that it wouldn’t always be presented in the same format, but there are actually some practical reasons for this.
For example, runway headings and markings are represented in magnetic headings, and so it would make sense that the ATIS or AWOS/ASOS would also be represented in magnetic headings so that it’s apples to apples. It wouldn’t make sense to be landing on runway 33 (magnetic heading of 330) and the controller give you a true heading wind direction that you have to convert in your head to calculate the crosswind component.
On the other hand, some instances make sense that the winds would be listed in true headings and leave it up to you to calculate the magnetic wind direction. For example, while you’re en route, since the magnetic variation can change as you travel, it makes sense that the winds aloft would be reported in true headings since those winds are over a general area that might have a magnetic variation change underneath it.
The adage “if you read it, it’s true. If you hear it, it’s magnetic” is a helpful starting point but there can be some confusing exceptions to this rule. For example, you can both hear a PIREP from ATC and also read one in a number of places. Winds listed in PIREPs are actually in magnetic headings, even if it was written. They don’t convert them from magnetic to true when read over the radio.
Because there are some confusing exceptions like this, I like to think of it more practically based on the situation. Why would it make more sense to have a true or magnetic direction in this instance? Well, to answer that, let’s go through some of the different situations where winds are reported in true vs. magnetic headings.
METAR:
METAR (translated from French roughly means Aviation Routine Weather Report) winds are listed in true headings, per AIM 7.1.31.b.5:
“The wind is reported as a five digit group (six digits if speed is over 99 knots). The first three digits are the direction the wind is blowing from, in tens of degrees referenced to true north, or ‘VRB’ if the direction is variable.”
Honestly, this is the only wind that didn’t quite make logical sense to be as to why it would be a true heading. As you’ll read later, ATIS/AWOS/ASOS are listed in magnetic headings and that seems to make practical sense when using in the traffic pattern and selecting the appropriate magnetic runway heading.
But METARs are also listing local winds for an airfield, so why would we need to convert it from true to magnetic? I couldn’t find a good answer for this online or in the AIM, and so I called flight service and talked to a weather briefer to pose the question – why are METAR winds for an airport in true headings while the ATIS for that exact same airport would be in magnetic headings?
After putting me on a brief hold he came back and pointed me to chapter 7.4 of The Federal Aviation Administration (FAA) Surface Weather Observer Program, Order JO 7900.5D that says “Local displays of wind direction are always in reference to magnetic north. Direction must be converted to true for observational purposes.”
At this point in the phone call I’m pretty deep in the weeds, but I appreciated him taking the time to point me in the right direction. Basically, it comes down to the fact that a METAR qualifies as an observation, which have winds that are reported in true headings.
TAF:
TAF (Terminal Aerodrome Forecast) winds are also reported in true headings, per AIM 7-1-30. Also, here’s a snippet from the always handy PHAK (Pilot’s Handbook of Aeronautical Knowledge):
“Forecast wind—the wind direction and speed forecast are coded in a five-digit number group. An example would be 15011KT. The first three digits indicate the direction of the wind in reference to true north. The last two digits state the wind speed in knots appended with “KT.” Like the METAR, winds greater than 99 knots are given in three digits.”
TAFs are generated by forecasters. According to the above, “Local displays of wind direction are always in reference to magnetic north. Direction must be converted to true for observational purposes.”, TAFs would fall into the “observational purposes” category. At least METARs and TAFs both list winds in true headings, if that makes it any easier to remember.
Winds Aloft:
Winds Aloft are reported in true headings. The FAA’s Student Pilot VFR Navigational Planning courses says:
“Winds aloft are provided at specific reporting stations for various altitudes in the FD or winds aloft weather product. In ground school you learn how to interpret these reports and extrapolate between the altitudes given to derive an estimated wind direction and velocity at the altitude that you are planning to fly. Remember that these winds directions are given in relation to true north, not magnetic north.”
The PHAK also covers winds aloft being in true headings.
I think the rationale for this is twofold. First, because it qualifies as an observation as discussed above. Second (and what makes more practical sense to me) is that winds aloft are listed over a generalized area, and that area might have a magnetic variation line running down the middle of it. For this reason, they can’t tell you the exact magnetic heading of the winds at altitude over that area that has multiple magnetic variations within it.
If you are planning a cross country trip, take note of where the magnetic variation changes and when you’d need to factor that into your magnetic heading calculation.
Interestingly, magnetic variation is re-assessed every five years by NOAA (National Oceanic and Atmospheric Administration) when they issue a World Magnetic Model.
AWOS/ASOS and ATIS:
AWOS (Automated Weather Observing System), ASOS (Automated Surface Observing System), and ATIS (Automatic Terminal Information System) all report winds in magnetic headings. AIM 7-1-12-d-3 has a note that says “Wind direction broadcast over FAA radios is in reference to magnetic north.”
Furthermore, going back to the “Local displays of wind direction are always in reference to magnetic north. Direction must be converted to true for observational purposes.”, AWOS/ASOS and ATIS are not formed by human observation and are just a local display of wind direction, therefore they magnetic headings.
A practical reason that these would be listed in magnetic headings is because the runway directions are also listed in magnetic headings. As mentioned earlier, it wouldn’t make sense to listen to the AWOS wind direction as you are approaching an airport and have to convert that from a true to magnetic heading in your head to determine the most favorable runway to use.
(Using that same argument, it seems like METARs should be in magnetic headings. But as we’ve discussed, since they are an observational report, they use true headings.)
PIREPs:
PIREPs (Pilot Reports) list winds in magnetic headings, per AIM 7-1-20 table 7-1-7:
Why are these magnetic? Well, pilots are reporting wind directions based on the magnetic heading they are flying.
Furthermore, wind components presented by a PFD (primary flight display) like in the G1000 or Aspen Evolution 1000 (I fly with one of these in my 182), for example, are in magnetic headings because it’s all in relation to what direction the aircraft is flying, which is a magnetic heading. When making a PIREP, pilots are not doing mental math to convert the winds back into true headings.
This can cause an exception to the “if you read it, it’s true. If you hear it, it’s magnetic” phrase, in that you can read PIREPs in a number of different places, however winds in PIREPs are still magnetic (they don’t convert them to true headings when putting them in written format).
Reported by ATC over the radio:
As a last catch-all, mentioned earlier was AIM 7-1-12-d-3 that has a note that says “Wind direction broadcast over FAA radios is in reference to magnetic north.” This might be part of where the whole “if you read it, it’s true. If you hear it, it’s magnetic” came from.
Just know that if for some reason ATC is going to read off to you a METAR or a TAF for an airport, those winds would be in true headings. I can’t think of a great situation where they would read the METAR and not the ATIS for a field, but just keep that in mind.
Practical Application
You might be thinking “so what? Where I live, the magnetic variation is limited and so mixing up true vs. magnetic headings might not be that drastic.” If that’s you, I can relate. Where I live, the magnetic variation is only 3 degrees, so it’s barely noticeable.
However, the funny thing about airplanes is that they go places. Even if you aren’t flying in an area where there is a big difference between true and magnetic north, chances are at some point you will.
For example, several years ago I had the opportunity to go up to Alaska and get my seaplane rating in Talkeetna with my dad who is also a pilot (I posted of videos we took in the super cub on floats on our YouTube channel here and here).
The magnetic variation in Talkeetna is 17 degrees! Whereas I can get lazy in Texas flying around with only 3 degrees, 17 is a big difference.
Since winds are reported in intervals of 10, 17 degrees of variation is basically a 20 degree difference in my estimated wind heading if I forget to apply (or not apply) magnetic variation to calculations.
That can mess up things like cross country flight planning (how is heading 17 degrees in the wrong direction going to turn out?), runway selection (20 degrees is enough to be the difference of a 90 degree crosswind and a 20 degree quarterly tailwind), and crosswind components (20 degrees of difference in a 30 knot wind is the difference of 5+ knots of crosswind component, which could put you outside of the aircraft’s maximum demonstrated crosswind, or more practically, your personal limits and abilities of controlling the airplane).
Conclusion
Where you’re flying today there might not be enough magnetic variation to force you to remember the difference of how winds are reported. But just like I experienced, you might fly to a place that has dramatic magnetic variation and if you aren’t disciplined about remembering which winds are true and which are magnetic, you could get yourself into a bind.
A good pilot is one who is always learning. Always adding to the memory bank the knowledge but supplementing it with application. Hopefully wind direction is now one of those things we’ll be able to remember and apply – it matters!