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Flightsummer

747: False Indications

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1. Who knows the reason for this false indication of the Touchdown Zone Indicator? The barometric pressure is 29.92 and the altitude at EDDH is 54 feet. See image 1.2. And who knows the reason for the difference between the heading of the indicated runway and the heading of the correct lined up airplane? EDDH runway 23, heading 231 degrees. See image 2.Thank you for your help.


Kind regards

Hans-Joachim Wennemeier

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I'm a bit confused.. I don't see a problem with any of the indicators..Number 1********The altitude is indicating 70 feet roughly.. so that's just 16 feet over the actual height.. I mean I could think a couple of reasons why that would be..a - the aircraft altimeter sensors are not within the undercarriage.. they'll be in the body of the aircraft fuselage and that will probably be 16 feet or more off the ground.. b - weather within FS2004 is not that precise.. and the altitudes of the airfields are not that precise either.. There are lots of things that are not simulated with FS2004.. sloping runways.. no runways is perfectly flat and they all are in FS2004.. I think you might be expecting a little too much from the simulation? The indicators are pretty close to me and I'd be happy with their readouts..Number 2********The difference is tiny, at 15 miles we're looking at a difference of perhaps 500 metres.. I would say that again.. the exact values are for runway heading are probably slightly off in the simulation... and you will always have a tiny discrepancy.. I don't know what it's like in the real world, but the heading and display looks ok to me and I'd be happy to take off.How do you know you're correctly lined up. i.e. perfect? Personally when I line up the pmdg 747 I can NEVER get a perfect line on the runway, it always needs tweaking with the rudder.. I usually use the first N1 to 70% to get a slow roll and make quick adjustments to get the line then apply TO/GA after I've done that..Also if you look at your display you're actually lined up on a part of your SID.. an intercept heading, and not the runway heading.. It looks like you intercept the vector to FU after 500 feet and that won't be on the runway heading.. as a result it deviates slightly. If you could zoon in further you'd see the flight plan you have follow the runway heading (which is 229 degrees) till you see (500) which is the 500 feet marker for the turn to the intercept heading to FU, then from this point forward it would leave the runway heading perhaps 2 degrees or so to the right.. What you've done is line up on the vector rather than the runway because it's the longer portion of the flight plan you can see on the ND.. You're not lined up with the runway heading itself which is what you should be..It looks like you're flying the BASUM 8B SID.. which is direct runway heading 229 to 500 feet manoeuvre height.. then direct to FU on 230.. continue with that heading to the 208 intercept to BASUM.. So the instrument looks right.I must say that I think these displays look fine to me.. I really can't see a problem with what is displayed.. I think the accuracy you're after is a limitation of the MSFS simulation and not a fault with the PMDG product...Hope that helps..Craig


Craig Read, EGLL

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Hi Craig,thank you for your very detailed respons.There are two reasons why I asked this question here. First, some weeks ago there were no reason to ask question number one, all was as it should be: the altitude was indicated between 50 and 60 feet and - more important - the touchdown zone indicator was in one line with the current altitude indicator. Second, all other airplanes show the correct altitude of about 54 to 57 feet, now as before. You have explaned why there are altitude differences. So we can forget this issue. But why does the TZI show such a big difference? If I would set 29.89 instead of 29.92 the indication would be correct. At other places this difference was 29.87 to 29.92 - and that is a really big difference, I think.To my second question. You are right, it's only a small deviation of about two degrees. And therefore I assume that there are differences between the various datas which come together: from the afcad drawing (31


Kind regards

Hans-Joachim Wennemeier

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In that case I'm really not sure.. but on my charts the runway is 229 degrees.. if you have a look at Navigraph you'll see.. and the SID supports your ND display.. as for the TZI.. I really don't know but it looks ok..Craig


Craig Read, EGLL

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"But why does the TZI show such a big difference? If I would set 29.89 instead of 29.92 the indication would be correct. At other places this difference was 29.87 to 29.92 - and that is a really big difference, I think."Not sure what the problem is here....TDZ yellow marker will always indicate the height of the runway (as specified in the FMC nav database). It is a fixed value.. in this case, about 55'. The only variable is your barometric setting, which will move the altitude tape, but it won't move the TDZ from 55' on that altitude tape. You have selected 2992, but you haven't specified if the actual baro pressure at that time of day was 2992 or something else (Are you using live weather updates?). Live weather updates generate rapid changes to pressure... and can make changes only a few seconds before touchdown... when it's too late to adjust your baro setting.Note that on the real aircraft, you can put in a company route which may have the wrong departure airport... in which case, the TDZ will show the wrong height for your departure airport.Hope this helps.Cheers.Q>

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"You have selected 2992, but you haven't specified if the actual baro pressure at that time"Indeed, I have. The situation was the standard atmosphere, within the FS-weather and within the FSUIPC. And therefore the TZI should be in line with the horizontal line, but is not. And I don't know why. Does anybody know?Back to question 2. Now, after some tests and investigations, I'm cocksure that the reason for the deviation between the FS heading and the FMC heading is the differend magnetic declination between the FS navdata (which are based upon the magnetic declination from 1993) and the FMC navdata (which base upon the magnetic declination from 2005/2006). In this case (EDDH) it is 2 degrees. And that is what the ND shows. And that's the same reason for the differences between the FS and all the current charts. Responsable for all that is the file "magdec.bgl" within the "scenerybase" directory. And now my recommendation: A few days ago Herv


Kind regards

Hans-Joachim Wennemeier

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