777:True North Oriented VORs
Thread Starter
Joined: Aug 2007
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From: Hong Kong
777:True North Oriented VORs
ok...new to the tripler....flipped thru the books but no joy...
how does the tripler handle true north oriented VORs? does it distinguishes these with mag north VORs? is the ND picture corrected for these at all? thanks folks.
how does the tripler handle true north oriented VORs? does it distinguishes these with mag north VORs? is the ND picture corrected for these at all? thanks folks.
Do you have an instrument rating?
Joined: Aug 2004
Posts: 548
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From: US
Interesting question, you might want to post it on the Canada forum. As I understand it there is some lat up north where it all switches to to true north as magnetic is totally skewed. I know for a fact that at least one airline up there purchased a fleet of TP's that could not accomodate this and the planes were essentially useless for IFR. (Unless you cheated and used your handheld Garmin etc but that hey that never happens)
I'm guessing that they do have this covered as a lot of the transpolar routes are on the triple.
20driver
I'm guessing that they do have this covered as a lot of the transpolar routes are on the triple.
20driver
Joined: Jun 1997
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From: auckland, new zealand
The 777s I fly have a push-button switch just to the left of the lower centre screne that allows switching between true and mag. Fromthe FM:
"Pushing alternately selects the heading reference for the PFDs, NDs, AFDS, and
FMCs.
NORM –
• normally references magnetic north
• automatically references true north when north of 82°N or south of 82°S
latitude or within the vicinity of the magnetic poles (PFDs, NDs, and
FMCs)
• provides no reference for AFDS roll modes other than LNAV when north
of 82°N or south of 82°S latitude or in the vicinity of the magnetic poles.
TRUE – references true north regardless of latitude.
When the AFDS roll mode is HDG SEL, switching the heading reference switch
from NORM to TRUE or TRUE to NORM engages the HDG HOLD mode.
When the AFDS roll mode is TRK SEL, switching the heading reference switch
from NORM to TRUE or TRUE to NORM engages the TRK HOLD mode."
"Pushing alternately selects the heading reference for the PFDs, NDs, AFDS, and
FMCs.
NORM –
• normally references magnetic north
• automatically references true north when north of 82°N or south of 82°S
latitude or within the vicinity of the magnetic poles (PFDs, NDs, and
FMCs)
• provides no reference for AFDS roll modes other than LNAV when north
of 82°N or south of 82°S latitude or in the vicinity of the magnetic poles.
TRUE – references true north regardless of latitude.
When the AFDS roll mode is HDG SEL, switching the heading reference switch
from NORM to TRUE or TRUE to NORM engages the HDG HOLD mode.
When the AFDS roll mode is TRK SEL, switching the heading reference switch
from NORM to TRUE or TRUE to NORM engages the TRK HOLD mode."
Joined: Aug 2003
Posts: 3,833
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From: Sale, Australia
Got to love Pprune for the education it gives one. Found the following http://www.faa.gov/other_visit/aviat.../info07002.pdf
so the question I have is how widely spread is the practice of orientating them to true north, and by what criteria is the practice deemed necessary? Looking at all my maps (out of date now) I could find none orientated with respect to true. Thule was still at mag, but note the FAA note is dated 2007 so is this a recent innovation?
so the question I have is how widely spread is the practice of orientating them to true north, and by what criteria is the practice deemed necessary? Looking at all my maps (out of date now) I could find none orientated with respect to true. Thule was still at mag, but note the FAA note is dated 2007 so is this a recent innovation?
Thread Starter
Joined: Aug 2007
Posts: 8
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From: Hong Kong
To Brian:
Thule is exactly the type of VOR i'm referring to. And for your info Thule has been true-north oriented for at least couple of years.
cribble:
thanks. i'm well aware of that the 777 has the push-button for switching all the reference on the navigation system to true headings/tracks, right in front of the captains seat. but the complications of true north oriented VORs is more than that..
i should clarify the scenario:
let's say the ND is in map mode and heading reference is "NORMAL" (mag north oriented), and you fly by Thule (THT) VOR which is true north oriented.
question now is:
how is the VOR needle displayed on the ND?
is it displaying the raw data from the VOR (which would results in a mismatch between the needle direction and the VOR position on the ND)?
or does the navigation database knows that Thule is true north oriented and the picture is corrected for that (i.e. wrong raw data information is displayed if you try to read the numbers under the VOR needle but a directionally correct needle on the ND)?
it's pure technical interest coz it's all GPS primary these days, but on this topic... how will the 777 FM response to that? will it attempt to do a position update from true north VORs (not knowing it is true north oriented?), which would then result in a grossly incorrect position update?
(to those who haven't flown the long range version of the Airbuses...the navigation database on the airbus can distiguish between true north and mag north VORs. and the display on the ND are always corrected for that, no matter it's a mag north VOR on a true north display or the vice versa.)
maybe the Continental guys will know about this.
Thule is exactly the type of VOR i'm referring to. And for your info Thule has been true-north oriented for at least couple of years.
cribble:
thanks. i'm well aware of that the 777 has the push-button for switching all the reference on the navigation system to true headings/tracks, right in front of the captains seat. but the complications of true north oriented VORs is more than that..
i should clarify the scenario:
let's say the ND is in map mode and heading reference is "NORMAL" (mag north oriented), and you fly by Thule (THT) VOR which is true north oriented.
question now is:
how is the VOR needle displayed on the ND?
is it displaying the raw data from the VOR (which would results in a mismatch between the needle direction and the VOR position on the ND)?
or does the navigation database knows that Thule is true north oriented and the picture is corrected for that (i.e. wrong raw data information is displayed if you try to read the numbers under the VOR needle but a directionally correct needle on the ND)?
it's pure technical interest coz it's all GPS primary these days, but on this topic... how will the 777 FM response to that? will it attempt to do a position update from true north VORs (not knowing it is true north oriented?), which would then result in a grossly incorrect position update?
(to those who haven't flown the long range version of the Airbuses...the navigation database on the airbus can distiguish between true north and mag north VORs. and the display on the ND are always corrected for that, no matter it's a mag north VOR on a true north display or the vice versa.)
maybe the Continental guys will know about this.
