Wind indication in HSI does not consider magnetic variation
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It seems that the wind indication in the upper left area of the HSI does not consider magnetic variation. Recently on a flight from BGSF to CYFB where the magnetic variation is around -26° the wind was indicated in degrees true, not degrees magnetic. Thank you for looking into this.
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Hey BlueSky...Not sure if this helps but from this forum post
The general rule is:
If you read it, it's true. If you hear it, it's magnetic.
All charts and textual sources (METAR, TAF, winds aloft, surface analysis charts, etc) use true north as the reference.
ATIS/AWOS/ASOS broadcasts, or any information a controller gives you over the radio, is magnetic.
Also there's no mention in the EFS-50 EHSI doc about whether the vector is True or Magnetic, indeed it's clearly articulated it's approximate only
https://www.bendixking.com/content/dam/bendixking/en/documents/document-lists/downloads-and-manuals/006-08485-0000-EFS-50-Pilots-Guide.pdfExtract
When the aircraft is equipped
with the appropriate LNAV
equipment, an optional full time
wind vector indicating approximate wind direction and speed
may be displayed in white in the
upper left corner below the
selected course. Wind vector
information will be available only
when valid data is provided by
the LNAV. The information provided by this vector is advisory
only. It is NOT intended for use
during approach as critical flight
data because it will become inaccurate during altitude changes.Do you have a reference somewhere that states it should account for MagVar?
Cheers
James -
Thanks James, for this detailed reply.
No, I don't have a reference which states that the information should be magnetic, it was just an assumption that directional information within one single instrument should not be mixed. The EHSI indicates a magnetic course and therefore it would be wise to also indicate the wind vector as degrees magnetic, otherwise the visual interpretation could be incorrect, especially when the magnetic variation is large.
On the flight I mentioned, the wind was coming from almost abeam, the indication in the EHSI, which now appears to be “degrees true”, told me that this wind direction gives a TAIL wind component, whereas the interpretation of the wind vector on another instrument, which gives the wind vector as “degrees magnetic”, told me that this gives a HEAD wind component. I'm not a r/w pilot, so maybe I miss an important information, but from my point of view (also it is stated in the manual that this is just an approximate) it is kind of confusing. -
Yeah I'm not sure there is a right or wrong here, perhaps someone with RW experience would know or Nick if he sees this? Seems like Bendix King are probably covering themselves for exactly this type of scenario as well by saying it's not for critical phases of flight. Interesting one though, got me thinking what the vector is using on say 737/A320
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Not familiar with your equipment, but… Real World. Is the HSI mechanical or is it an MFD (multi function display)? If it is an MFD there may be an option to display the ‘HSI’ hdg as magnetic or true. That will be indicated my a ‘M’ or ‘T’ symbol, typically shown at the top of the display. What ever the case, unless otherwise indicated, a wind arm / speed would normally follow the convention of the hdg source for the HSI display. But to further complicate matters. The computer wind direction/speed can be derived from all manner of data; TRK, G/S, TAS, EAS, OAT, etc, etc. What (wind and speed) is shown is that which is being experienced by the a/c in flight, so in the real world it would be at altitude - NOT surface wind.
I hope that helps, sorry if it doesn’t. BTW, at extremes of latitude some equipment manufacturers require the a/c to be flown with reference to true hdg only.
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