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Autopilot usage - Course and Track/Heading

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Autopilot usage - Course and Track/Heading

Old 17th Aug 2020, 14:36
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Autopilot usage - Course and Track/Heading

Hi,

most likely a stupid question but since its kind of specific I couldn't find an answer via google.
I have read several articles regarding heading and course and understood these as far as I can tell.
However the following scenario is still unclear to me.

If ATC tells an heavy aircraft with autopilot like a 737 or an A320 to fly heading 360 the pilot enters this on the "HEADING KNOB" of the MCP/FCU.
Is the aircraft then flying a heading/track or a course (with usage of wind data)?

Because if 2 planes are flying together on the same radial and both planes get the ATC order to fly heading 360 the planes will not both stay on the same radial if there is a different wind component for both planes.

So my question is..is the HEADING KNOB actual flying courses with the aid of wind data or are these really headings?
In latter case, can these wind deviations not cause problems?

Thanks!

Best regards Andi
737Andi is offline  
Old 17th Aug 2020, 14:48
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If ATC tell you to fly a "heading" then you fly a heading (referenced to magnetic north)

If ATC give a heading to avoid other traffic/slot you into a traffic sequence then the basic idea is that the wind will effect all aircraft equally, the wind vector doesn't vary that much over short distances once you get away from the surface of the earth....

​​​​​​ When you are being vectored to intercept an approach then the controllers are usually smart enough to know what effect the forecast or reported wind will have on the shape of their radar pattern and will adjust the headings they give accordingly..

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Old 17th Aug 2020, 15:26
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I can't remember Boeing, but Airbus FBW can fly a plain heading, or a track, both of which are selected with the heading knob on the FCU. There is a pushbutton to select between Heading/Vertical speed and Track/Flight path angle, (The FD presentation becomes a Flight Path Director and looks significantly different to distinguish between the two modes). The heading is a magnetic north referenced heading; the track is also referenced to mag north but takes wind drift into account to keep to the selected track.

A330 (and maybe newer A320 family) can be referenced to True North.

As wiggy says, if ATC ask for a heading, they want a magnetic referenced heading and they are making the allowance for wind. If you were to fly a track instead of a heading, you might eventually come into conflict with nearby aircraft on headings.
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Old 18th Aug 2020, 05:39
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Originally Posted by 737Andi View Post
So my question is..is the HEADING KNOB actual flying courses with the aid of wind data or are these really headings?
In latter case, can these wind deviations not cause problems?
By the way, not a stupid question at all.

But then, the heading knob is commanding the autopilot to fly a heading, not a course, so it is not adjusted by on board wind data. Except in the airbus world if it is switched to track/FPA, which is normally never the case except for certain approach procedure (selected/selected non precision approach). Wind data in general is known to the ATCOs, and if they don't know it they ask us for a spot wind check. Except for the UK headings (also called vectors) are used mainly in the terminal area (and sometimes for a short tactical adjustment enroute), and will be changed by the ATCOs if and when needed. So they can react to trajectories that are not as they expected it, and with that to wind wind changes.
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Old 18th Aug 2020, 07:23
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If ATC say "Fly heading xxx" you fly heading XXX. Whether you're using the autopilot or not is irrelevant.
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Old 18th Aug 2020, 13:36
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On 737: If you select heading, it's only magnetic heading, no track. It shows you Heading Bug on Nav Display to follow manually or directs Autopilot to follow in HDG mode. To fly a Track, you would i.e. select LNAV mode to follow Legs. Or use waypoint/bearing and fly an appropriate Heading to intercept and follow the track.
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