Wrong VNAV calculation

[x_robert]

Hi there,

new to the IXEG 737 I am experiencing some FMS issues which navigates me to FL300 35nm from my Destination runway which has an elevation of 2235ft.

The result of this calculation: Unable to get down in time.

So, why is that?

It is like that because the VNAV calculation algorithm obviously does not correctly recalculate the VNAV profile when I alter the route.

 

You can check this out yourself by programing the following route into the CDU:

(Database is the default one  AIRAC 1509)

DEP KSNA RWY 02L

DEST KLAS RWY ILS01L

Waypoints: DAG

No SID/STAR

Approach Transition into KLAS: WOPMA (ILS01L)

 

Now if you put that route into the CDU there will be a disconnect between DAG and WOPMA which I did clear by connecting the DAG to WOPMA waypoints.

Let us take a look at the VNAV calculations then:

DAG - FL300 (65nm to WOPMA)

WOPMA - FL300 (5.7nm to CEDAX)

CEDAX - 11000A

All the following waypoints have soft altitude restrictions (xxxxA - ABOVE) down to the runway 01L. (Which of course has a HARD restriction because the runway elevation is 2235ft)

Except TRREY (7000) and NODIY which (as the runway) has a HARD 5300ft.

 

Only if I manually alter the altitudes of the waypoints CEDAX (from 11000A to 11000) or SHANQ (9700A to 9700) the altitude of at WOPMA gets calculated correctly.

If I alter the (third) waypoint after WOPMA which is KRUDY from 8000A to 8000 the altitude at WOPMA is not updated and hence wrong. 

 

Why is it so hard to get these calculations right?

My logic tells me that no matter what the user puts into the route the calculation has always take into account that the plane has to get down to the runway within the performance envelope of the Aircraft. If this cant be achieved it has to report : unable

 

Another thing which I will never understand is why it is not possible with these FMS systems (all developers)  to do a simple direct calculation from the Departure Airport to the Destination Airport.

KSNA DCT KLAS (Distance xxx nm CRZ FL300) Basta (Like every GPS system can do). Thoughts?

Oh and another one: Why is there not a current DATBASE included when purchasing a product of that price?

 

Regards

Robert (a bit disappointed and looking forward to the next update)

 

 

 

 

 

 

 

  

 

 

 

Edited December 21, 2016 by x_robert

[Litjan]

1 hour ago, x_robert said:

Why is it so hard to get these calculations right?

That is a very good question!

I don´t know where to start. Really...