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Guest Concordeguy

Heading hold

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Guest Concordeguy

Hi when i push the heading button to hold a heading, the aircraft stays 2-3 degrees short of the heading I want to be at. E.G.9I want heading 250 it goes to heading 247)Please help me.Christian

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Is this 747 or 737?Are you pushing heading hold or heading select?Remember that the ND displays track and not heading. Are you sure that you are not confusing track for heading? Try another display like the full VOR (hdg up instead of track up) and see what the heading is there in comparison.CheersSteve


Cheers

Steve Hall

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Hi, Just a side question. WHat is the purpose of HDG HOLD when the 747 has HDG SEL. You can HOLD a specific heading with heading select function, why brother using heading hold. The only 2 likely situations I can think of is during Go Around and T/O, while you want the AP to maintain rwy heading so you can focus on other stuffs like gear and flap. However, a good pilot should tune the HDG display in the MCP to the rwy heading before T/O and LDG, so they can just press the heading select button. thanksben

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There is a difference although it is not great. As the track varies the heading bug needs to be manually alligned. If a clearance is received that says maintain current heading all you need to do is press heading hold. Otherwise you would have to allign the heading bug and then press HDG SEL. As I say not a biggy but convenient. Also good on engine failures after TO. Tuning the heading bug to the departure runway is good practice however once you are in the air drift comes into play and with HDG SEL this needs to be manually compensated for.CheersSteve


Cheers

Steve Hall

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Guest PUB802

Hi,The same is happening to me (in both 747 pax and 747F). I was just about to comment this issue.I will try to explain. If I select, lets say, heading 250 in the MCP, in the heading display of the ND I see 247 and the heading bug (magenta) is pointing to 247 not to 250.It is as if the system (the heading display and heading bug) were working as the ground track pointer showing me the drift angle.By the way, in the heading reference switch I have selected Magnetic North (ND displays MAG)I will try to post a screenshot as don

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Guest Ray51

Heading hold and heading select will not correct the aircraft's flight path for winds. So you will see the selected head such as 250 in your example line up with a small triangle while the "track" will be the course over the ground due to wind drift. Using LNAV will fly the aircraft with data from the INS and GPS to correct your track for wind drift.Ray

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Gents-You guys are confusing the presentation of TRACK and HDG on the navigation displays....Each of the different display methods for the NAV display will show you one of two presentations: TRK UP or HDG UP.In HDG UP mode- you will see HDG|___|MAG at the top of the display. (Or TRU, if you selected that manually) When in HDG UP mode- the heading the airplane is flying is vertically centered on the nav display.Conversely- in TRK UP mode- you will see TRK|___|MAG at the top of the display. When in TRK UP mode- the GROUND TRACK is vertically centered at the top of the display.In ZERO WIND conditions- the track and magentic heading will always match because the airplane isn't being pushed sideways if the air isn't moving.Now- for the following two images i have placed the airplane in HDG SEL mode flying a 000 heading with 25 knots of crosswind from 090. As such, you can see the wind vector in the upper left of the display.In HDG UP mode (i think i selected APP or VOR- i forget now) you will notice that the HDG is vertically centered on the display- and the grey ground-track lubber line is displaced to the left because the airplane is flying a constant heading but is drifting left with the movement of the air mass.http://www.precisionmanuals.com/images/for...HDG_UP_MODE.jpgIf you switch to the MAP mode- you will see a TRACK UP display- and as such the layout changes slightly so that the GROUND TRACK is vertically centered on the display. The airplane is still locked to the autopilot and is still flying a 000 heading- but what you are seeing is the track the airplane is flying when the computation winds/drift accounted for.http://www.precisionmanuals.com/images/for...TRK_UP_MODE.jpgNote in the TRK UP mode how there is a little white triangular heading carret? That is showing you the heading currently being flown- and your magenta bug is showing you the heading selected... Lots of information there!Now- if I suddenly take the winds OUT of the equation on the same display- look what happens:http://www.precisionmanuals.com/images/for...k_Mag_Match.jpgViola! Ground track and heading both match- which makes sense since the airplane is not drifting on account of the movement of the air mass!You will find that the HDG UP mode is more intuitive when being vectored around for finals- but if you get accostomed to reading the NAV MAP mode- it really isn't hard to sort out in your mind.You will also find that they grey ground track line is ALWAYS helpful when hand flying an approach- because if the ground track line lays perfectly in line with the approach course- you aren't drifting left/right of the localizer course....


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Guest PUB802

Thanks for your clarification. I have been "flightsimming" since 1997 with PS747 and then I changed to PMDG the day of the release of 747 QoS (I have the PS747 manual with your prologue as a quick reference! )I thought I had a pretty good knowledge on 747 aircraft but it seems I was wrong. My hobby has been on stand-by this last two years due work overload. Now that I have some free time again and resumed the hobby I am amazed (or frustrated) how quickly I have forgotten the things I learnt during many many hours of study.In this case I had forgotten that in MAP I am in Track mode and in VOR/APP in Hdg mode. BasicWell, it is time to stop moaning!Many thanks for the tip of using the track line as a cue to align the Queen with the runway. I like to hand fly the approaches and will help a lot during cross winds.Best Regards,Scott

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