Precise calculation for VDP in nautical miles.
 

This is how I calculate VDP in nm.

VDP in nm = (MDH-TCH) / (106.13 x des. angle)

MDH = Minimum Descent Height
TCH = Threshold Crossing Height

From the diagram below. If using a calculator:

980➖293➖55➗106.13➗3.5

[IMG]http://i779.photobucket.com/albums/y...smchrdnze.jpeg[/IMG]

Dadanawa,

Two decimal points! I am impressed.
However, how do you monitor progress after you commence descent? Do the mental gymnastics need to be repeated?

I do not know what aeroplane/FMS you are referring to but those aeroplanes fitted with a ND and a 'end of descent' indication of some sort do tend to make a lot of this work academic I would have thought?

I just read the profile off the chart, pretty simple.

That close in, below the MDH (A), I hope you're looking out the window at the PAPI, Scat! :ok:

I used to do stuff like that when i was young and enthusiastic. It faded very fast and since then i just do what the manual says: Fly the CDFA profile to DA, if i see something i continue, if not i go around. And yes, even on non precision approaches it is a DA nowadays, we dont use MDAs anymore.

PAPI? Luxury!

CDFA to a DA for APV or DDA for MDA charts using VNAV as guidance.
VDPs are things of the past really...for those who are still using VS as a vertical mode or worse....

VS? Luxury!

Aerocat,
Obvioulsy CDFA technique may or may not be used depending on aircraft type/systems.
Never heard of it until i joined the airlines...progress never stops:E

Hi Actus,

I guess it becomes important when the VDP is before the missed approach point. Also some countries do not have the height/distance table. For that, I use a spreadsheet program.

It becomes becomes important if you have to calculate your own CDFA descent path or use dive and drive. For aircraft with fairly modern (30 years or so) systems that is mainly a thing of the past.

I have to say i'm intrigued about the missing distance/altitude table, could you give an example of an international airport? Others might not be in my database.

de facto, oh we fly a CDFA, it's just that with a VS mode that can't be adjusted without using "SYNC" it is often easier to just hand fly it and follow the profile with good support from the PNF.

We should keep this in perspective. We are talking about flight below the MDH. From that point, we should be flying with reference to the PAPI/runway perspective, not a profile.

Dadanawa,

A spreadsheet??

I do not know what job you have now but you should consider being an approach designer or a nav data base coder.

From a 'planning' point of view, i.e. on the ground before flight, I am with you 100% but when it comes to 'flying' this stuff, I tend to take the uneducated 'nike' approach and 'just do it'.

A bit too flippant I will admit but I think you get my drift.

Indeed Bloggs, I was interpreting the VDP as being the whole descent not just the visual bit below DA/MDA. It is all a bit academic if you're just working out a descent point to take you from 500ish feet to the TDZ!

Hmm, right, below MDA we have to fly visually anyway, in our company we have to switch off the FDs to enforce that as well.

I would go with actus reus' approach there. Just do it and fly the damn airplane, its not rocket science.

Hi Denti. For example, LTAL LOC 18 in Kastamonu, Turkey. Using Jeppesen, not LIDO.

Ok, i only have LIDO charts available that do have a distance/altitude table for that approach. I guess it is just a service LIDO provides then vs Jeppesen just taking the AIP information without adding anything.

I agree with all. Below MDH, of course PAPIs, VASIS, visual, etc.

Just for parts of the world that do not have the height/distance table, or on the abscence of VNAV, you need to have this information to work with for CDFA.

CDFA Spreadsheet
 

I use this when the information is not provided on the chart.

https://lh3.googleusercontent.com/-p...2/IMG_1325.JPG