FMC 'FIX' page

[tva164]

Hi all,

1. What is the Airbus equivalent for the Boeing FMC 'FIX' page?

2. What are the various uses of this page and associated techniques. It would be helpful to know about your practical experiences here.

Thanks.

[Sink Rate]

We mainly use the fix page to cross check the FMC derived position against actual "raw data" position.

Whatever waypoint or beacon you put inthe fix page will result in your FMC bearing and disyance from it being displayed.

We put in a VOR in the Fix page and compare the range/bearing with that displayed onthe Nav set.

Other uses for the fix page are to highlight a particular waypoint (the fmc puts a green circle around the point on the map page) for example critical waypoints in an emergency turn procedure or go-around.

[B clam]

Don't know about the airbus (well, not yet but just about to convert). In addition to that above we also use the fix page for fuel checks. If we have been cleared direct to a waypoint but want to do a 1/2 way fuel check we can put the relevant point into the fix page and then select 'abeam'. This will create a posn on the present track which we can convert into an active waypoint. ;)

[NorthernSky]

The fix page allows you to 'draw' some of the MSA analysis onto the map. Eg, if the MSA is sectorised within 25nm, being 2300ft from 060deg bearing to 180deg bearing, and 3700ft outside, you can replicate this on your map display by drawing those radials and a 25nm arc.

However, as Jeppesen insist upon drawing terrain charts using bearings to the field, not from, you have to do a lot of quick 180 addition and subtraction.

Jeppesen charts used to be really good.

And then they started printing them on flame-retarded paper. :D :D :D :D :D

None of the 'bus kit I have used features a FIX page. It is the ONE thing I would take from a Boeing and put in a 'bus!

[ 19 August 2001: Message edited by: NorthernSky ]

[Checkboard]

On long sectors and ETOPS flights you can also draw a couple of range circles from your diversion ports.

Make both circles the same size, and juggle the distance so that the two circles intersect on your route, and you have made a (nil wind) Critical Point.

[Redback]

On the B744 we use the Fix Page during the cruise to give us a display on the ND of where our nearest two diversion fields are.

It's also handy to find out where other aircraft in the area are heading, just enter one of their reporting points and you can then even use the BRG lines to draw their track.

During arrivals into airports where the descent path gets close to the CTA steps we can draw them in.

When flying a NPA we often use the range arcs to remind us where any height constraints are. Handy with the dynamic arc to check if you'll satisfy the constraint.

But most importantly, we can enter a time that is then displayed with a green circle on the the position along our route where we will be at that time. Used as a reminder to call the other guy/girl back from their break!

Great little tool that page.

[MasterGreen]

From my notebook - some fix page data that you might be interested in ...

FMC FIX Page stuff

Interesting page, FIX. Much misused and misunderstood. Here are a couple of interesting limitations.

The range circles have a maximum value of 511nm. This is 2 ^ 9 and is a computer thing. 2 ^ 8 (2 to the power of 8) is a recognized number and equals 256 (Think RAM). The 2^9 is a numeric processing limit of the processor employed (equivalent to a Intel 486 for those interested) and is of course 512. Why 511? – well 0 to 511 is just that.

When you generate a Bearing Line it also has a finite dimension. In this case 699.9 nm. There is a lovely story that goes with this. It is not absolutely true, but it does make the point.

We are talking about the old English expression Plain Sailing. Now in common usage this phrase has come to mean something straightforward and easy. In its’ original form it was an expression used in navigation (Plane Sailing). The origin dates back to our old friend Gerardus Mercator (1512-1594).

Prior to the mid 16th century, voyages of any length were really just a case of – “take a lot of food and water and we will see you when we see you”. But as is the case with many of the major changes in history, a whole lot of important developments came together at about this time. The back stave gave way to the sextant. Chronometers became reasonably reliable and maps were becoming more than just fancy interpretations of even more fantastic tales. The art of (reasonably) accurate navigation was born. However it was quickly apparent that on long voyages you needed to use a Great Circle on one of Mercator’s Maps to save yourself some time and grief. But on short voyages a Rhumb Line would serve equally well. Depending upon which mathematical school you subscribe to, the limit of a Rhumb Line is 699 nautical miles. Thus the Plain Sailing expression relates to the simpler (plane) mathematics that could be applied to short voyages. Whereas the longer journeys required the more complex mathematics of the spheroid.

The Fix page generates a straight line, so this is a reasonable limitation. Future updates, I am (well ?) reliably informed, will have the BRG line limit increased to 1200+ nm. It will then have to be a curved line to show a great circle. I will be suitably impressed when I see this. Older (non Pegasus / PIP FMCs have a limit of 400 nm on this BRG line). This info is just for interest. All newer FMCs are PIP/Pegasus.

This 699.9 nm limit is also reflected in our ability to generate impromptu waypoints. You cannot take a Range/Bearing offset from a database point to beyond 699.9 (call it 700 for cash – some allow that) nm – try it.

[Herod]

Checkboard. Adjust for wind and they become (roughly) equal-time circles to the two airfields

[MPH]

Hi Guys,The FIX page apart from providing you with the bearing and distnace from a specified fix to the aircraft plus the capability to obtain predicted down path crossing times,distances and altitudes from a user defined radial off the reference fix.This could be a waypoint, a waypoint/course intercept point on the ACT F-PLN or an abeam point.
It's also great for useing as a fix page for a visual circuit reference i.e downwind/base and final calculations. Just punch in the four letter airport code plus the rwy designator and you can from their on, just put in the abeam/final approach fix. ;)

[Intruder]

The FIX page can also be used to verify FMS position. Set a VOR in the FIX page, and compare the FMS-generated bearing/distance with the raw VOR/DME data.

[Busta Level]

NorthernSky - The 330 has a fix page. Works like a dream. And you don't have the inconvenience of having to fly a Boeing to get it! :)


Cheers!

Busta