Madeira

[B747-400]

Hi,

I'm afraid I missed some infos, how to create an fly over waypoint. Searched, but no success.

I want to create the curve from FUN211/6 to GELO and ROSRO, as per the charts.
But instead of the correct (yellow) course, I got the magenta line and a zig zag at ROSRO.

What am I doing wrong?

THX
Hans

[Jeroen Hoppenbrouwers]

As far as I remember, the 747 FMC does not have the option for the pilot to program a fly-over waypoint. It can have these waypoints as part of a procedure from the database, but pilots cannot make them. There are many other procedural things pilots cannot program, probably because the authorities/Boeing consider this unsafe. Either you use a pre-programmed, complicated procedure that has been vetted multiple times, or you use something simpler.

Hoppie

[Hardy Heinlin]

Hi,

as far as I recall, this arc is an RF leg. You'll get this specific arc radius if you have the NG FMC and load the approach from the database. The RF arc radius is fixed and stored in the database; it won't change with your groundspeed which is the case on normal leg turns.


Regards,

|-|ardy

[Markus Vitzethum]

> There are many other procedural things pilots cannot program,
> probably because the authorities/Boeing consider this unsafe.

If I'm not wrong, the accuracy of the lat/long data stored in the FMC database for any given waypoint (and in the source ARINC424 database, for that matter) is higher than the accuracy of a waypoint which is entered via the FMC scratchpad. As we know, for scratchpad entries, positions are only accurate to 1/10th of a minute of arc, or 0.1 mile. (And obviously, conditional waypoints, L/R turn preferences, fly-over information, procdure-tuning of navaids, all of which are essential database features, are not available.)

One might argue that for RNAV procedures, editing might work (with waypoint stored in the DB)- there is a reason why editing/modifying terminal procedures is discouraged. E.g. modifying a SID from the database might lead to controlled flight into terrain. See this report:
https://www.thb.gov.hk/aaia/doc/CPA86%20Final%20Report.pdf

[B747-400]

Thx for all you inputs, Gents!

Btw: a good reading, Markus!

Regards
Hans

[John H Watson]

I got the magenta line and a zig zag at ROSRO.

Zigzag lines are a common feature on the 747 ND

[Jeroen Hoppenbrouwers]

What does the AFDS actually fly if you push it towards such an artwork?

[Hardy Heinlin]

According to the logic, the FMC will activate the next waypoint when 50% of the turn arc is passed (which happens at the abeam line to the active waypoint), at which point your LNAV will start to capture the next leg. In other words, LNAV won't overfly the peak of the zigzag.

[B747-400]

As workaround I created some place bearing distance waypoints, giving an excellent curve.
So, my son and I can work on our LPMA approaches 



Regards
Hans