how does the ILS really work on the B757/767
Paul MacDougall
just wondering if anyone is familiar with the inner workings of the ILS
system and how it integrates with the FMC....ie if you dial in the correct
localizer frequency but mis-set the front course setting how does the system
work or not work... does it matter if you mis-set it only 10 degrees verses
80 degrees....my AOM is not very helpful and I know this system has screwed
a few people...
thanks for you help in advance
Paul
Ron Parsons
>just wondering if anyone is familiar with the inner workings of the ILS
>system and how it integrates with the FMC....ie if you dial in the correct
>localizer frequency but mis-set the front course setting how does the system
>work or not work... does it matter if you mis-set it only 10 degrees verses
>80 degrees....my AOM is not very helpful and I know this system has screwed
>a few people...
The FMC will complain if you tune the wrong frequency for the selected
runway, but doesn't check the course set in.
There are a number of aeronautical myths about what will happen with
various amounts of misset course but no hard data that I know of.
Once on the Loc, the FMC does drop the DME/DME or VOR/DME updating and
uses the LOC.
Some of the myths and scares you might hear date from very early versions
of FMC software and may or may not have any value on any particular
version.
Ron
Luitbert Schindhelm
> just wondering if anyone is familiar with the inner workings of the ILS
> system and how it integrates with the FMC....ie if you dial in the correct
> localizer frequency but mis-set the front course setting how does the system
> work or not work... does it matter if you mis-set it only 10 degrees verses
> 80 degrees....my AOM is not very helpful and I know this system has screwed
> a few people...
Well I do not exactly know the Avionics system of a B757 works.
But generally, an ILS station will give you only one Radial (and that
should lead you directly to the runway).
It does not matter which course you have selected, it is only a good
practice to dial in the correct course. But this has only an
informational value and does not affect then accuracy of the indication.
It is only important, as you said, that you have dialled in the correct
frequency.
That is by the way on of the differences to VOR stations, where it is
essential that you also set the correct Radial if you want to reach your
destination.
Regards
Luitbert
N.B.
What is an AOM?
Si Zarco
localizer would centre but you would need to know what direction you had to
be heading in. If you offset it by 10 degrees, it may prove to be more
dangerous as you may not notice it, although you would realise on 80 degrees
as when you were flying 'down' the arrow, the localizer would just fly
across your HSI.
I think. (hey, I'm here to learn, not teach!)
--
Si
Awfully sorry, I'm an English posh git, anyone for Tea?
sza...@nofuckinspamglobalnet.co.uk
ICQ:732738
Ralf Sipple
> just wondering if anyone is familiar with the inner workings of the ILS
> system and how it integrates with the FMC....ie if you dial in the correct
> localizer frequency but mis-set the front course setting how does the system
> work or not work... does it matter if you mis-set it only 10 degrees verses
> 80 degrees....my AOM is not very helpful and I know this system has screwed
> a few people...
sorry, don't know, but I have a similar question:
Today I was flying an ATR72. We were cleared ~30 nm from FCO
to intercept the localizer 16L and as the the indication
this far far out is often somewhat inreliable I decided to
follow the extended centerline with LNAV. I monitored the
ILS indication on the captain's CRT (in the ATR you have
either RNAV or conventional NAV indication, but not both)
and confirmed by that that I was precisely on LOC and GS.
Closer to the field I switched my display to L/V (conventional NAV).
This caused the LNAV mode to go off, the AP was in basic lateral
mode (maintain bank). I armed APP. The course selector was
set 50 deg off to the right fron the correct course (162deg).
As I was already precisely on LOC and GS they both captured
immediately. But then the unexpected happened: The A/C banked sharply
to the right (the direction the course selector was pointing to)
and came off the LOC to the right. I then turned the course
selector to the correct approach course and the AP re-intercepted
the LOC.
It appeared to me that the AP used the set course as an initial
value for a heading which may be appropiate to follow the
LOC (in this case it wasn't).
I once discussed a maater with a B737 captain. He said that
his company rules called for flying an approach with the ND
in APP mode. He said he likes to keep the ND in MAP mode
to improve situational awareness. The reason for the rule
to have APP mode displayed is that he couldn't see the course
dialed in MAP mode.
However, the deviation signal from the localizer (opposed to VOR)
is completely indepent fom the selected course.
Has anyone tried similar things? How does your plane behave?
Viele Gruesse,
Ralf
--
Ralf Sipple | Fax +49-711-7777206 | sip...@gmx.de
D-70794 Filderstadt| Anrufbeantw. +49-711-7777208| pgp key on request!
Neil Wagner
On 30 Mar 99 01:53:19 , "Paul MacDougall" <pm...@simcoe.igs.net> wrote:
>just wondering if anyone is familiar with the inner workings of the ILS
>system and how it integrates with the FMC....ie if you dial in the correct
>localizer frequency but mis-set the front course setting how does the system
AFAIK, there is no setting of the front course by the pilot. You
tell the FMS you want to execute a certain approach and it will
auto tune the correct frequency and present you with the correct
final approach course.
__________________
Neil - n...@gte.net
Paul MacDougall
I have been on the B757/B767 for about two years and yes you do have to dial
in the localizer frequency and the front course heading manually. the FMC
will not autotune it...
I have been in a situation where the wrong front course heading was dialled
in and the airplane did not capture the localizer, even though you could see
it on the ADI display....
no I didn't watch it go through the localizer, used heading select to
correct and then realized that the wrong front course was set in. So I go
back to my original question, why didn't it capture? the system obviously
needs the proper heading to capture. the AOM (aircrew operating manual)
doesn't say much, so I wondering about the inner workings
Paul
JWizardC
>What is an AOM?
Aircraft Operating Manual.
TheFNG
B757DC9
The pilot manually sets the course and frequency on the ILS tuner box.
There is no warning from the FMC if you set them wrong. If you set the
wrong course, the airplane and autopilot doesn't care. It just chases
the needle when in LOC or BCRS mode. Just like what happens when the
course is miss-set on an aircraft with an analog HSI.
On the next generation FMCs, ( B777/744) the FMC does indeed tune the
ILS.
And thats the facts, Jack.