FMC "INTC CRS" question
Thread Starter
Joined: Jun 2011
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From: Belgium
FMC "INTC CRS" question
Hello
,
I've a question concerning the "INTC CRS" feature :
When we are under radar vector for approach, I usually ask to set the FAF of the runway on top of the leg page and select the localizer course on the LSK 6R (INTC CRS). What does the VNAV deviation scale indicates when we perform this?Is it the deviation between the current altitude and the FAF altitude?Or the deviation from the altitude we should have when we intercept the LNAV route with the actual heading?
Thank you very much for your imputs
,I've a question concerning the "INTC CRS" feature :
When we are under radar vector for approach, I usually ask to set the FAF of the runway on top of the leg page and select the localizer course on the LSK 6R (INTC CRS). What does the VNAV deviation scale indicates when we perform this?Is it the deviation between the current altitude and the FAF altitude?Or the deviation from the altitude we should have when we intercept the LNAV route with the actual heading?
Thank you very much for your imputs
Joined: Oct 2006
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From: Ankh Morpork, DW
There was a thread on this a couple years back. I *think* it was "decided" that the FMC transposes you laterally onto the FAC and does not include any offset for a base or downwind. So, if you were on a base 5 miles from the threshold, 3 miles from the centerline, it would say you're at 4 miles. (3-4-5 triangle.)
Now I need to look that up again. That doesn't sound right, now that I think about it.
Now I need to look that up again. That doesn't sound right, now that I think about it.
Last edited by ImbracableCrunk; 1st July 2012 at 19:09.
Joined: Oct 2005
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From: Sweden
Never tried this as i don't really need a VNAV Path, but if you're on an intercept course and you extend the centerline. I guess you could just click LNAV, then it will draw a line to the extended centerline and probably give you an accurate path then go back to HDG.
Again i've never actually done this for real.
Again i've never actually done this for real.
Joined: Jun 2000
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From: last time I looked I was still here.
I'd always thought the PROG 1 distance was the nm's from present position on your intercept HDG to capture the magenta line and fly the planned route thereafter. Your altitude relative to the required path to achieve the next alt constraint generates the VNAV deviation.
Joined: Mar 2012
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From: Somewhere
I think it calculates from aircraft position to that FAF and then the rest of the flight plan regardless of your aircraft track or heading.you can check it out by setting intercept course to at FAF and you will see the same distance at progress page in different intercept track even your track is from the runway(outbound ).
Another method to check,by selecting the same track to intercept but change your intercept point (may be FAF IF or the others),the distance is changed (on aircraft or simulator ).
Another method to check,by selecting the same track to intercept but change your intercept point (may be FAF IF or the others),the distance is changed (on aircraft or simulator ).
Last edited by Noknoipobin; 2nd July 2012 at 16:14.
Joined: Oct 2006
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From: Ankh Morpork, DW
Never tried this as i don't really need a VNAV Path, but if you're on an intercept course and you extend the centerline. I guess you could just click LNAV, then it will draw a line to the extended centerline and probably give you an accurate path then go back to HDG.
Again i've never actually done this for real.
Again i've never actually done this for real.
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From: engineer at large
First, since you reference LNAV, and referencing a localizer, what type of approach procedure are you using?
Second, I would ask where you are getting altitude, and location of the FAF for the runway?
Second, I would ask where you are getting altitude, and location of the FAF for the runway?
Thread Starter
Joined: Jun 2011
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From: Belgium
Thanks everybody for your explanations so far
It's an ILS approach
Sorry, I meant FAP...
First, since you reference LNAV, and referencing a localizer, what type of approach procedure are you using?
Second, I would ask where you are getting altitude, and location of the FAF for the runway?
Last edited by adri737; 2nd July 2012 at 21:44.
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From: engineer at large
Okay, so that clears it up a bit...
The difficulty here is that the ac, using this method, you will intercept the ILS beam, perhaps 'at or above', then the ac will drop, to re-acquire the beam, especially when using baro-vnav to ILS intercept...
This is all very possible, but is certainly 'outside the box'...
The difficulty here is that the ac, using this method, you will intercept the ILS beam, perhaps 'at or above', then the ac will drop, to re-acquire the beam, especially when using baro-vnav to ILS intercept...
This is all very possible, but is certainly 'outside the box'...
Thread Starter
Joined: Jun 2011
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From: Belgium
Okay, so that clears it up a bit...
The difficulty here is that the ac, using this method, you will intercept the ILS beam, perhaps 'at or above', then the ac will drop, to re-acquire the beam, especially when using baro-vnav to ILS intercept...
The difficulty here is that the ac, using this method, you will intercept the ILS beam, perhaps 'at or above', then the ac will drop, to re-acquire the beam, especially when using baro-vnav to ILS intercept...
Per Ardua ad Astraeus
Joined: Mar 2000
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From: UK
So complicated, so confusing, and in effect absolutely **** useless (since ATC will probably never send you that way) which is why I never used the 'extend the centreline' (luddite!) but always knew where I was and what I height I needed to be. Much simpler. Is it that difficult?
Unfortunately it became the 'darling' 'clever trick to show' for those TC's who presumably did not really know where they were and every F/O came out of the sausage machine programmed to push the buttons and then not really know what to do with it.
The very best in FMC vertical guidance was with an un-executed (dotted white on 737) leg to a point, but that sadly fell out of favour with de management and became a no-no..
Long live range to waypoint and the three times table. Why complicate it?
(since ATC will probably never send you that way) which is why I never used the 'extend the centreline' (luddite!) but always knew where I was and what I height I needed to be. Much simpler. Is it that difficult?Unfortunately it became the 'darling' 'clever trick to show' for those TC's who presumably did not really know where they were and every F/O came out of the sausage machine programmed to push the buttons and then not really know what to do with it.
The very best in FMC vertical guidance was with an un-executed (dotted white on 737) leg to a point, but that sadly fell out of favour with de management and became a no-no..
Long live range to waypoint and the three times table. Why complicate it?
Thread Starter
Joined: Jun 2011
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From: Belgium
Thank you OK645 for your good explanation!
I'm speaking about the classic but I suppose it's the same as in the NG?
And how is the profile computed if we don't put the VNAV cruise altitude on the FMC? Imagine we "just" use LVL CHG and not VNAV...
Let's say we are on a 8Nm downwind (HDG SEL and ALT HOLD and the FAP is on top of the leg page with the correct intercept course) and the VNAV deviation indicates 2000ft high ... How is this value calculated?
As to your specific question (assuming you're speaking NG here)...
And how is the profile computed if we don't put the VNAV cruise altitude on the FMC? Imagine we "just" use LVL CHG and not VNAV...
Let's say we are on a 8Nm downwind (HDG SEL and ALT HOLD and the FAP is on top of the leg page with the correct intercept course) and the VNAV deviation indicates 2000ft high ... How is this value calculated?
Thread Starter
Joined: Jun 2011
Posts: 11
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From: Belgium
So complicated, so confusing, and in effect absolutely **** useless 
(since ATC will probably never send you that way) which is why I never used the 'extend the centreline' (luddite!) but always knew where I was and what I height I needed to be. Much simpler. Is it that difficult?
Unfortunately it became the 'darling' 'clever trick to show' for those TC's who presumably did not really know where they were and every F/O came out of the sausage machine programmed to push the buttons and then not really know what to do with it.
The very best in FMC vertical guidance was with an un-executed (dotted white on 737) leg to a point, but that sadly fell out of favour with de management and became a no-no..
Long live range to waypoint and the three times table. Why complicate it?
(since ATC will probably never send you that way) which is why I never used the 'extend the centreline' (luddite!) but always knew where I was and what I height I needed to be. Much simpler. Is it that difficult?Unfortunately it became the 'darling' 'clever trick to show' for those TC's who presumably did not really know where they were and every F/O came out of the sausage machine programmed to push the buttons and then not really know what to do with it.
The very best in FMC vertical guidance was with an un-executed (dotted white on 737) leg to a point, but that sadly fell out of favour with de management and became a no-no..
Long live range to waypoint and the three times table. Why complicate it?
Last edited by adri737; 3rd July 2012 at 19:40.
Per Ardua ad Astraeus
Joined: Mar 2000
Posts: 18,575
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From: UK
It does not need a 'VNAV' cruise entry - it uses current altitude. I was told it computed the 'direct to' vertical profile with no allowance for heading or turn radius, but that could be wrong - as I said, I never used it. If that is the case, the only time it would be meaningful would be when you were on that track, so I would wager that '2000ft high' would be just about perfect..That is why the 'un-executed' route was always more accurate as it 'drew' the turn.
