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Mnps Nats Crossing Techniques (fmc)

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Mnps Nats Crossing Techniques (fmc)

Old 25th Dec 2008, 18:35
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Mnps Nats Crossing Techniques (fmc)

Can somebody tell me if any airline operating B777 across the Atlantic selects true tracks on the FMC and Track Sel on the MCP,and if so what are the reasons for that as this procedure is not mentioned in the B777 manuals.
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Old 25th Dec 2008, 20:09
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Because we did it like that in 1978?

Personally, I think we should fly true tracks all the time, none of this heading rubbish (magnetic, especially) now we all have GPS.

That aside, we have the ITTs and distances on our plogs, which are not subject to so much variation (ha!) as the magnetic info. We also have backup manuals containing this information and it is in true. I think producing all this paperwork keeps somebody in a job, which is probably the real reason why we do it...
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Old 25th Dec 2008, 22:11
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thanx fullwings
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Old 27th Dec 2008, 05:01
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On our B744's we are track up ALL the time.
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Old 27th Dec 2008, 17:24
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Delta Air Lines flew True Track up until about five years ago. I understand that they run in Mag these days and for what reason, I do not know? Track or Heading up is an option for the B777 customer to determine when they order the airplane from Boeing. I assume it is a pin selectable option and thus can chnged at will along with a Boeing Engineering authorization. I'm sure someone will chime in here but I think BA uses the Heading up in lieu of Track up. I fly the B777 sim quite often and it always pays to check just what config is playing that day in the sim. Personnaly I think all long-range nav should be conducted in True, but I learned sometime back, that my opinion does not count for much these days.
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Old 27th Dec 2008, 17:29
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Can someone please explain why it would make any difference in a 777?
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Old 27th Dec 2008, 20:13
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I'm not sure where your coming from with that question? Be it a 777, 767, 747 or any other Boeing product, it would be the same. I was thinking along the lines of how your paper flight plan was produced and the way the crew did it's waypoint passage procedures. If your flght plan is built using magnetic headings then the point becomes somewhat moot. If on the otherhand you are using true data it presents a more logical presentation on both the chart and the FMS. Keep in mind that the FMS/GPS is using one mag var data base, the flight plan computer uses another mag var data base and so on. By using true, you eliminate the small but none the less real differences along your route of flight. If on the other hand your one of those who just engaes LNAV and never cross checks the navigation process, all the above is meaningless.
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Old 27th Dec 2008, 21:44
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Well, I normally allow the LNAV to follow the route (lat and long) and check that my pos as plotted on a chart lies on that route. It matters not to me or my a/c whether it flies mag./true or grid, as long as it stays on the line, surely? I do not sit there working out variation every 10 mins. to make sure it is steering the correct mag heading +/- 5 degrees.

My 'route', both PLOG and FMC, is built on rhumb lines between waypoints, my PLOG shows true and mag tracks. The differences in variation data bases are pretty well irrelevant since the a/c will track the lat and long of the route regardless of variation, and even if it had NO variation db it would stay on track, wouldn't it?

Now, if I lose ALL my nav kit and have to DR across the area, apart from my being just a bit screwed, THAT is different and then variation becomes a significant factor.
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Old 28th Dec 2008, 12:00
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PLOG? What does that stand for if I may ask? Plotting chart perhaps
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Old 28th Dec 2008, 14:13
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Typically PLOG = Pilots LOG.

In BA on the 747-400 the display is heading up. I have flown track up as well, but personally believe that heading up is more intuitive wrt drift etc, it is after all what we all start up using.

The True vs Magnetic is a separate debate. Our flight plans are produced with both magnetic and ITT (Initial True Track) data. When we fly in Oceanic airspace we switch to True reference (ie Headings and Tracks shown on the ND will be referenced to True North. We check our tracks and distances vs True for these portions of our flight plan, using the ITT outbound from the waypoint, checked against the flight plan and the NATS track message for the day as necessary.

Personally, I can see a time in the not too distant future when everything will be referenced to True North, after all, all the FM(G)C does is apply variation from a lookup table to determine Magnetic Hreading anyway. Runways usually don't change their orientation, so runway numbering changes would be a thing of the past. At the moment commercial aviation progress in this would appear to be held up be non INS/IRS commercial aircraft and general aviation.
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Old 28th Dec 2008, 14:17
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A bit of confusion here. "Track-up" and "Heading-up" is a feature of the ND and is airline specific and can only be changed by engineering, i.e. on the ground. Boeing provide a switch on the instrument panel marked "True/Mag" which is switched to "True" to allow navigation checks after waypoint crossing (OTS) and compares initial true track (ITT) against actual track on the ND. An airlines' SOPS may recommend selection of "True" for the entire track crossing, while some airlines may not. The use of "True" is important in high latitudes due to large magnetic variation.
Having operated B744s with "track-up" and others with "heading-up", either is simple to get used to - the important usage is for navigation accuracy, as LNAV will only track what the user inserts into the FMC.
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Old 28th Dec 2008, 17:18
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Excellent point and if I failed to define the True vs. Mag. issue as you just did, my appologies. It's interesting to note that Boeing recomends leaving the True/Mag switch in Mag during polar ops?
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Old 28th Dec 2008, 17:50
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My two cents:

NATS procedures and techniques are contained in the NATS Manual, found at NAT PCO.

In the B777, the change of MAG to TRUE and vice-versa is automatic. The switch remains in NORMAL at all times and you only see the change when the airplane is flying in that "window" (formed by the 130W and 080W Meridians and by the 70N and 82N Parallels).

Leave the LNAV engaged when flying OTS or Random routes; less chance to drift off track if you would do otherwise. LNAV flies the track for you.

The only time Boeing recommends you to set the switch to TRUE is when you are doing the track/distance check before the flight.

Heading up or Track up is a pilot's choice; it doesn't affect the auto system.
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Old 28th Dec 2008, 19:14
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Some serious confusion here I'm afraid. No where in any Boeing FCTM, FCOM or any Boeing document do they suggest checking the FMS as you have mentioned. Perhaps it's within a company document or SOP. Not saying this is a bad procedure, just not a Boeing procedure. It would depend on your paper flight plan having True data on it and I suspect that for those operators that are using Mag for crossing, the True data might not be there?

The Mag or True option is up to the operator and Boeing could care less how you do it. That's why the switch is there along with the requirement that you operate in True while in the AMU/NCA (Northern most Canada). As previously mentioned Track up, Heading up is a customer option, not a flight crew procedure. Yes you could fly in track by using the HDG/TRACK switch on the MCP, but I'm not aware of that being an acceptable Boeing procedure of oceanic crossing.

Last edited by Spooky 2; 29th Dec 2008 at 15:42.
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Old 29th Dec 2008, 10:32
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I think Spooky has it right. This whole true/mag. bit is just down to airlines' internal procedures - it has no effect of the navigation equipment as far as flying from A-->B. You could be referencing Galactic North for all the difference it makes.

In companies with a lot of history, they probably started with astro-nav, then worked their way up through IRSs and LORAN towards GNSS and a lot of the procedural cruft has stuck. Now we use ADS(-B)/CPDLC/GPS, etc. many of the "checks" we do are redundant - not all of them, however. We have both mag. & true data on our plans but use true due to database issues as mentioned in previous posts.
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