Confusing FMS Altitude Calculations

[freeze1058]

Hi,

I'm a little confused about the FMS-3000 altitude calculation for legs where no manual constraint has been entered. Cruise level is FL270.

mv_b350_fms_01.jpg (79.38 KiB) Viewed 2246 times

SULED - 9000 in line with manual constraint entered for KLF
TADUV - 9000 in line with manual constraint entered for KLF
MILGU - 3000 (beginning of the STAR)
NOLNI - ----- (part of the STAR)
KLF - Manual constraint at 9000

To my understanding (from Boeing 737-800) the altitudes should display FL270 (cruise level) and then calculate intermediate values down to 9000 at KLF.

How do I need to interpret the given values? Where do I find the actual top of descend point?

Cheers,

Stefan

[KenG]

Did you enter the manual constraint at KLF?

Is it also part of the STAR?

What was your flight plan?

[matpietsch]

Hi Ken,

this happens with every altitude constraint (user or part of a STAR). All the waypoints prior get populated with the same altitude. Strangely enough this does not happen every time. At least to me.

[KenG]

Is it repeatable with a certain flight plan, or totally random?

[freeze1058]

Hi,

my initial flight plan was:

EDDN ERET7K ERETO DCT TABAT T202 MILGU MILG3S EDDB

Didn't have time to retry same or alternate route but will report once tested.

Regards,

Stefan

[matpietsch]

Is it repeatable with a certain flight plan, or totally random?

Once it happens again I will post the route here.

[freeze1058]

I just re-entered the route posted above without additional constraints:

mv_b350_fmsr_01.jpg (79.09 KiB) Viewed 2204 times

mv_b350_fmsr_02.jpg (75.64 KiB) Viewed 2204 times

mv_b350_fmsr_03.jpg (67.59 KiB) Viewed 2204 times

mv_b350_fmsr_04.jpg (78.74 KiB) Viewed 2204 times

Cannot identify much of a logic behind the values:

DN103: Instructs for descend (2250) between the constraints
Main leg: 3000 in line with first approach constraint PIKOV at 3000
MILGU/NOLNI: No values as part of the STAR
KLF...: Unclear value 2487 during transition from STAR to approach.

[freeze1058]

BTW, the auto-calculations only appear after selecting an approach.

What is the real-world procedure? Should approach already be selected during flight plan entry at origin?

[KenG]

Generally, an approach is assigned by approach control, so very rarely would you select an approach on the ground. However, that is still not correct logic for the FMS.

[matpietsch]

Is it repeatable with a certain flight plan, or totally random?

Hi Ken,

here is my current issue (flight still running).
Route: EDDF -EGKK

SOBR1Y SOBRA Y180 BITBU Y181 DEMUL M624 BUB L608 DENUT L610 TEBRA TEBR1G

TEBR1G Altitude restriction: 14,000 at ABTUM.

This is how the FMC legs page looks like with VNAV already selected:

2019-12-28_17-49-2-898.jpg (422.85 KiB) Viewed 2182 times

2019-12-28_17-49-5-832.jpg (421.73 KiB) Viewed 2182 times

2019-12-28_17-49-7-733.jpg (440.25 KiB) Viewed 2182 times

Is the down arrow at ABTUM actually correct? I don't know the PL21 in detail yet but I would think a down arrow means "at or below".

[KenG]

Arrows are the phase. Above or Below would have an A or B proceeding the altitude.

[jarek]

Down arrow indicates descend leg. SIDs get automatically Up arrow mark, STARs are marked with Down arrow.

[Heronjr]

Hi Ken,

this happens with every altitude constraint (user or part of a STAR). All the waypoints prior get populated with the same altitude. Strangely enough this does not happen every time. At least to me.

+1 and for every flightplan.

[kasten.amarant]

same problem ive mentioned here

http://milviz.com/forum/viewtopic.php?f=105&t=11467

I didnt see this topic here, otherwise i would have posted here

[matpietsch]

same problem ive mentioned here

http://milviz.com/forum/viewtopic.php?f=105&t=11467

I didnt see this topic here, otherwise i would have posted here

Actually they want an topic for every occurrence. So you did it right .