172 driver, thanks for that. I was just reaching for the razor blades and you saved me.
Dave_Phillips wrote:
Sometime I will write an article on how ILS glidepaths behave below 140ft or so. It may make some reconsider pushing below 200ft unless they have the right equipment and are properly trained.
Ok, now you made me really curious. Would you mind giving a short version of it here? And looking foward to that article.
In my very limited experience I recall that the GS is anything but stable in the last 100 ft or so but will start to oscillate quite a bit. That were my observations when I still had my IR valid many years ago. Alone for that it never occurred to me to use a GS below 200 ft, let alone lower.
I might guess that this has to do with the immediate proximity of the GS transmitter. At 200 ft you are still in a good distance, at 100 ft only very close to it and beyond that basically near the transmitter. With the beams overlapping, I can´t imagine how this should work that close by.
Mooney_Driver wrote:
In my very limited experience I recall that the GS is anything but stable in the last 100 ft or so but will start to oscillate quite a bit.
Even a CAT III autoland system will stop using the GS at about 50 ft and instead use radar altitude.
150ft actually.
My friend who is certified to fly these says that starting at 200ft, the signal of the radio altimeter is integrated with gradually increasing gain until 50ft, from where the GS isn’t factored in any more.
JasonC wrote:
It is my opinion based on my experience of both.
Well OK, that is hard to argue with of course. But it would still be interesting to know, why you perceive it that way? The reasons could be manifold, from the equipment you have, the technique you have been taught or anything else that really makes it easier for you. This is what I am interested in.
Airborne_Again wrote:
I disagree! I find CDFA much easier to fly.
At least I am not alone. ;-)
Aviathor wrote:
Most people tend to take acronyms for granted and do not realise they are exclusive.
Peter wrote:
150ft actually.
The Oxford Aviation Academy ATPL manual says 50 ft. I haven’t had the opportunity to try it for myself. 
TobiBS wrote:
Well OK, that is hard to argue with of course. But it would still be interesting to know, why you perceive it that way? The reasons could be manifold, from the equipment you have, the technique you have been taught or anything else that really makes it easier for you. This is what I am interested in.
I really dont know. I was taught D&D as everyone was in the 90s. At the FAF chop the throttle, get to the MDA and look for the runway. Pretty straightforward.
Compare that to a calculated descent with check alttitudes and V/S adjustments.
I just find it easier. But to say again, i think CDFA is better and that is how I fly.
I doubt it is equipment driven.
JasonC wrote:
Compare that to a calculated descent with check alttitudes and V/S adjustments. I just find it easier.
But to say again, i think CDFA is better and that is how I fly.
I never questioned this, I hope this was clear! In general my questions and comments are meant to get different views on a topic.
I doubt it is equipment driven.
This was just an example of issues that might be between your and my view of the things. Sometimes the exact same tasks with the exact same tools look hard to one person, while they look easy to another person.
I learned, that the regular 1nm step altitudes are for reference only, they are a help to not reach the decision altitude early
Test standard is +/- 100 feet at the DME/Altitude references, and you are expected to adjust rate of descent to be on target at the next DME checkpoint.
