VNAV Descent

[canadaclipper]

H0ello Captains. I purchased the wonderful IXEG 737-300 last weekend. Since then I have done 4 flights with it. My problem is that on each occasion the VNAV path seem to be approx 2,000 ft above the altitude constraint in the FMC. I have a lot of time with the PMDG 737-800  as well as the Zibo 737-800. I believe that I have everything set up properly for descent but I"m wondering if there is something that I may be missing with the 300. Any help would be appreciated. Thanks in advance.

[Litjan]

Hi canadaclipper,

the VNAV descent functionality is one of the areas where our logic is very "basic" - the vnav path works well if there are no restrictions on the descent, but currently restrictions can still throw our calculation off. We are planning a total rewrite of the VNAV logic.

For now it is required to keep a close eye on your descent calculation. It is ok to use VNAV, but if the calculation seems suspect or acts up, revert to FL CHG mode or even V/S.

I have made a video that shows how to calculate descents manually (it is one of the core competencies of real pilots - VNAV descents are not playing a huge role in real airline flying because often the path to be flown is not known beforehand).

When I used to fly the 737 Classic (for 10 years) I was the only one who ever used VNAV on descents (out of curiosity). I have never seen a Captain use it (in my 6 years as a copilot) nor have I seen a FO use it (in my 4 years as a Captain).

https://www.youtube.com/watch?v=hSemWBgRNnE

Cheers, Jan