Mike, I beleive I understand most of the HBY navigation system concepts(a fancy backwards counting odomoter of sorts to me), but still not sure on the meaning of the term "conditional" meridian and its relationship to the azimuth correction. As I understan it, this "conditional" meridian is the "magnetic" meridian (which is where you take the magnetic north as 0 deg.)determined with the declination value at the latitude in question. Now, I understand also that to define an orthodromic course in land, you need to define the course relative to a true reference system; which forces you to change directions at every meridian to maintain orthodromy (meridians are not parallel (like they seem with loxodromy or the so-called projections), or in other words, they converge at the poles; The change in direction being forced by the changing angles between meridians. The question I have is with the course agreement, I am not sure if the azimuth correction (delta a) at the points after the beginning point are due to magnetic variation or just the differnce between the angles between meridians or a combination of both. http://forums.avsim.net/user_files/94229.jpgThanks in advance for your help,regards,Mac.

Hi Mac,Read my navigation doc for AN24 for details. I posted yeterday night. Anyhow:A course is "orthodromic" (not true, not magnetic...) if the angle is measured to a non-local reference line. It can be either the magnetic or the true meridian of the point (waypoint) where you had aligned your GPK gyroscope.In practice you spin up and align your gyro at the departure airport. You adjust it to either true or magnetic North. If from that point you fly wihout any (MK, AK) correction the gyroscope will keep its reference and all courses it serves to all equipment will be relative to that reference meridian. It is good, because if you follow a given course relative to that fix reference direction, you will follow an orthodromic track (please do not ask for detailed math).If you aligned your gyroscope to the magnetic meridian then all courses relative to it will be called as OZMPU (ortodromiceskij zadannij magnitnij putevoj ugol). If it was aligned to the true meridian, it is calle OZIPU (ortodromiceskij zadannij istinnij putevoj ugol). The reference meridian is either magnetic or true, it depends on you.ZIPU (true starting course from one waypoint to the other) differs from OZIPU by the collected fork caused by true meridian convergence (azimut correction). Do not forget that this course will change while you proceed on the track because you collect additional fork.ZMPU (magnetic starting course from one waypoint to the other) differs from OZMPU by collected fork and by magnetic declination difference between your actual point and the reference point where you had aligned the gyro. Do not forget that this course will change while you proceed on the track because you collect additional fork and because of further spatial declination change.Details and pictures in my document.Gabor

Coool! :DThanks Gabor.regards,

Gabor already gave perfect answer, just a little additional info for practical usage in the Tu-154.You have the choice to fly on true or orthodromic course.To fly on true course, before takeoff you put the magnetic variation of the departure airport into the Correction instruments KM-5. And leave the Magnetic variation on zero in the NVU Calculator.To fly on orthodromic course - the other way round. Magnetic variation must be entered in NVU Calculator, but left at zero in the KM-5.In the real world, the second method is used - less possibility for error or failure of KM-5 instrument. Michael

>You have the choice to fly on true or orthodromic course.Maybe I am not right, or maybe I am just argue on terminology, but I think you always use orthodromic course on Tu-154. What you described is - as I underestand correctly - the difference between the reference meridian: either true, or magnetic. Then the course is either IZIPU, or OZMPU both is orthodromic.You can hardly fly on a true (not orthodromic) course. There is no equipments that shows you that and you wil then not follow a great circle. True course angle on a great circle is continuously changing. What is not changing is the course you read from the gyroscope. The course you follow using GPK mode is always (!) orthodromic as it is referencing to a distant (reference) meridian (either magnetic or true).I think it is mainly about terminology, but is important.Well, I should try that Tu-154! I would love!Gabor

Gabor,>> but I think you always use orthodromic course on Tu-154Yes, but this is exactly what I said what is done in real world !?It is a matter where you "carry" the magnetic variation. In the KM-5 or "inside" the courses in the NVU calculator. Take any example and calculate once with and once without the magnetic variation in NVUCalc, then you see the difference. You can see the KM-5 in the system diagram on page 28, this is the most easy way to see what it does. I have a hard time to put this in words with my German English ;).It is somewhat academic, because of course you fly on orthodromic course. I just wanted to mention, you COULD fly on true course if you should want to.I have to find a diagram to explain the term "conditional meridian". There is a nice one in the air_navigation*.pdf at avsim.ru, but I can't find it right now.Besides this, there could always be a misunderstanding on my side, I am sure I have also not discovered all the mysteries about that fascinating subject yet :)>> Well, I should try that Tu-154!That should be a must for everyone :). Mostly for the gorgeous feeling of flight, the navigation is just the cream on the cake.Yesterday I was flying with a friend of mine. He did the navigator job on a second monitor, by the book with RSBN corrections and the like. And we were talking the checklists in Russian (in the meantime we understand what we say :D).Finally I landed in Novisibirsk in really bad weather (low vis and a sh.tload of crosswind). Very smooth and relaxed on the flight director, with a PFC Jetliner Yoke (some kilogram weight on the axes) it is just a dream. I bet none of my imaginary passengers felt anything uncomfortable ;)Flight simulation at it's very, very best Michael

Micheal, I think Gabor's explanation is a bit more coherent, although not to say your manual is not. It just makes more sense to me his explanation, or the way he explains it (acronyms make sense now, even though I don't know the language). After reading his explanation in the manual of the navigation problem, it all makes sense. It seems a lot of the confusion is over terminolgy, specially on the definition of "course" as he explains. Thanks again for your help,regards,Mac.

Mac,yes, I fully agree, Gabors explanation of this complicated subject is excellent. I justed wanted to point out a specific difference in the Tu-154 (with that KM-5 instrument).However, the Tu-154 manual is already two months old, in the meantime I got a lot of useful feedback (also from you, just BTW) and infos, so a refined version 1.1. will be available soon, probably with the next PT Tu-154 version.Michael

Michael, How do you start HBY numeration? It is mentioned on your manual, but I can't find what steps are needed to actually do it. I must have missed it. Thanks in advance for your help,regards,Mac.

Mac,see screenshot (the switch with the white circle)RegardsMichaelhttp://forums.avsim.net/user_files/94424.jpg

Hey Michael,I'm doing the meridian transfer for the arrival airport manually, but I am not sure I'm doing it absolutely right. Could you post a step by step (with screenshots maybe?) description? I would really appreciate it. At the moment I get always a course change when I reenable the HBY and I'm sure I'm forgetting something somewhere.Regards,Daniel

Daniel,I'll do that, but for family reasons I have no time over the weekend. So I'm afraid that must wait a few days. Or maybe in the meantime someone else could jump in ?Michael

just noted, I totally forgot this thread. Sorry Daniel, but here goes :You need the TKS-P2, the USH-3 navigation instrument and both HSI. Open the Copilot HSI as well, it's good to see the process.Let's assume, you fly with a heading of 60 deg before the transfer. Your fork value might be +8, so you would end up at a 68 deg heading after transfer.On the USH-3 (see screenshot) you will notice two indications. The big needle with the plane symbol and on the outer scale a little triangular index.Now first disconnect the HBY mode by turning the navigation computer off. If not, during the trasnfer all glasses in the epassenger cabin might fall from the table :). But that way the plane will continue with the actual heading.First we will transfer the reserve gyro unit, which will deal with the Copilot HSI and the triangular index on the USH-3. On the TKS-P2, leave it in GPK mode and put the Korrektsija Switch to Kontr. Now use the button labelled ZADAT KURSA (see the white box in the screenshot). There are clickspots on both sides for (+) and (-). Now use the (+) spot to move the triangular index on the USH-3 exactly 8 degrees further. You can use the digital values to make that more exact.Now to the main gyro (Captain HSI and the big needle on the USH-3). Put the Korrektsija switch to osn and use the ZADAT KURSA again (same 8 degrees movement).Now click/hold the alignment button until the numbers don't change anymore (similar procedure as before takeoff). Then go back to the Kontr position of the Korrektsija Switch and click/hold the alignment button again.That's it, you're done.Michaelhttp://forums.avsim.net/user_files/95440.jpg

Thanks a lot Michael, now the transfer process is clear to me.GreetingsDaniel