CDU: Fly-By vs. Fly-Over waypoints

[stefanloss]

Hi fellow pilots,

one thing I noticed is that my CDU (Build 389) handles normal enroute waypoints as "fly-over" waypoints. This means that it commands the aircraft to fly directly over a waypoint instead of turning to the next leg shortly before reaching the waypoint itself (called "fly-by" waypoint). That of course results in the aircraft overshooting the planned track. After passing a waypoint, the aircraft has to re-capture the filghtplan.

As far as I konw, enroute waypoints should always be "fly-by" waypoints, while "fly-over" waypoints are only used for certain defined approach or departure routes.

Of course this is not such a big issure, but maybe there is a way to change this?


Best regards,
Stefan.

[Michael Carter]

For certain STAR's in Europe, fly-by waypoints are also used to keep aircraft in protected airspace and out of someone elses way. Many examples are available at the various airports.

Sorry, I can't help with your question about the automation.

I start my turn when the DME reads 5NM +/- depending upon wind speed and direction. That usually gets me to the next course centerline with a minumum of correction. Sometimes I'll have to use the wiz-wheel to figure a new WCA for the new course or I'll use bracketing.

[Hans Krohn]

Stefan,

do you set your cost index? That entry is required to calculate the magenta path correctly.

Hans

[rippey]

I have been meaning to ask the same question for a while. Normal enroute waypoints should be handled as flypast waypoints...the aircraft should only overfly waypoints designated as fly-over...they are usually only found in sids and stars as far as I know...not very often in north america, but seem to be pretty common in europe. I am assuming the FMS software in the boeings has a way to designate certain waypoints as flyover...I know honeywell FMSs in the aircraft I fly have that ability.

I have noticed the same behaviour with the PM cdu, it seems to treat all waypoints as flyover. I haven't found anything in the software allowing this to be changed.

[Hans Krohn]

they are fly-over if they are in a (more or less) straight line.
I do see the plane turning a bit before the waypoint, if the next is at an angle!

Hans

[Michael Carter]

I can't see flying right over a fix if a turn is involved like you said Hans.

A good example is the turn from UZ111 at OBIGA onto UL984. If you wait until over the intersection to turn you're liable to hit someone on Y863 heading for FFM.

Not much margin in congested airspace.

[Jackpilot]

""....do you set your cost index? That entry is required to calculate the magenta path correctly...""

By the way what are the usual values for it.
In some doc I have seen that it goes from 0 to 999 but apparently PM does not accept over 400 or so..
Anyone has precise info on that?

[stefanloss]

Hi all,

I always do the complete preflight setup. For cost index, I usually use 80 or 100. In fact, 80 was the poposed CI setting for the 767 PIC.


According to Bill Bulfer´s FMC guide, CI can be chosen between 0 and 500. The higher the CI, the shorter the flight time will be (for the cost of increased fuel and wear).

[Jackpilot]

thank you fot the info

[Hans Krohn]

I payed plose attention last nite:

When I reach a waypoint that implies a heading change, this is what happens:

1. the plane starts the turn BEFORE the waypoint
2. the waypoint drops (disappears from NAV display)
3. the magenta line is redrawn from the plane's position to the next waypoint
4. once the turn towards the new WP is complete, the magenta line is again redrawn.

Don't know if it works the same in the real plane, but it works for me... :-)

Hans

[pdpo]

Hans,

the working you described is the same I see in the airbus PM suite.
However I have complained about this to Enrico and send him the
needed screenshots to prove my point. When flying on autopilot
this behaviour is acceptable but once you fly an approach manually
and the MCDU cycles to the next waypoint dropping the wayopint from the
ND ... you loose the reference to it.... worse even when you have defined
several waypoints somewhat close to eachother and when the MCDU cycles
all the waypoints are removed from the ND and you loose all references to fly
unless you revert to traditional VOR/NDB navigation.....

PS : at least for airbus I know that the calculated path of the MCDU includes
the projected turn and the planes follows this path perfectly. When the
MCDU cycles to the next waypoint the previous one does not disappear
unless its outside of the range of the ND.

Greetz Peter

[mauriceb]

""....do you set your cost index? That entry is required to calculate the magenta path correctly...""

By the way what are the usual values for it.
In some doc I have seen that it goes from 0 to 999 but apparently PM does not accept over 400 or so..
Anyone has precise info on that?

Everything I read about this only mentions values of 0 to 100, with 100 being the least economical way (fastest performance). So I don't think that there is any point in putting in anything over 100 even if the CDU accepts it. I could be wrong though :)

Maurice

[Jackpilot]

0 to 100 would make sense... sort of percentage ...because why 500?

Any "lifesize" CDU specialist on that?

[stefanloss]

PS : at least for airbus I know that the calculated path of the MCDU includes
the projected turn and the planes follows this path perfectly. When the
MCDU cycles to the next waypoint the previous one does not disappear
unless its outside of the range of the ND.

Greetz Peter

That´s exactly how it should be in the 737 as well.