Peter wrote:
In traditional IR you hand fly everything. I was taught to hold the VS but of course that will give you the “glideslope” only if your GS is constant too. And you don’t know the GS unless you have a GPS (or DME).
I don’t see the problem. You start with the VS in the table. Then you have the following points for correction in the Shoreham 20 case:
Surely not difficult to establish a half way correct continuous descent. Getting to master this (without AP) was the bigger part of IR training.
And you don’t know the GS unless you have a GPS (or DME)
Know one IFR plane that doesn’t have at least a GPS today?
Yes but (in this context) you aren’t allowed to use a GPS on a traditional IR checkride.
Why do you need to know the GS?
The approach is required to have check altitudes and for this it will require navigation equipment such as DME or RNAV.
Peter wrote:
Yes but (in this context) you aren’t allowed to use a GPS on a traditional IR checkride.
You quotes the Shoreham RNAV 20 approach. You’re saying that one must not be flown with a GPS? 
I was allowed to use the GPS on my IR checkride. Or better, I put a DCT to the runway into it and while I was flying the NDB approach I glanced at the bearing on the (non moving map) GPS. Of course the examiner from the LBA saw that, and I was sure that he’d protest. He said: “well done, I would use any navigational source on board the plane too, and it would be quite stupid to have the GPS and not use it” :-)
This is off topic but shows the many cultural differences around Europe 
In the UK, a GPS was a total no-no until a few years ago. Currently AFAIK, you can use it and the autopilot on enroute sections. And my FAA IR was much harder – 100% by hand and nearly all partial panel. Two-VOR approaches (one for the inbound and one for the SDFs) done with one VOR receiver (not kidding).
But I have for a long time been hearing stories from e.g. Switzerland of the examiner telling the pilot to fly an NDB IAP using the GPS “because it is the right way”. But then Switzerland could do its own thing.
I don’t get it.
Approaches contain check altitudes. For those you need distance measuring equipment. The type of equipment required is indicated on the approach plate. It can be:
So where’s the problem? You verify your altitude and then you adjust your vertical speed and check on the next one. This is how we are taught to fly a NPA.
PS: Unless the instructor/examiner is an idiot, he will let you use the GPS for NDB manoevers for anything outside of “CAVOK practise”. Relying on an ADF when a GPS is available is stupid and not justified by anything.
You have no influence whatsoever on what the examiner will want you to do, and I am 100 % sure that many german examiners would not allow you to use the GPS on an NDB approach. But the one that checked me was not some bureaucrat from the LBA (CAA) but an experienced airline pilot who did it for them …
I real life, I’d always use the GPS and fly the approach coupled if it’s in IMC and use my energy and concentration to check what the system does. I am sure that a coupled IAP is safer than a hand flown, especially if you can take over any time if something goes wrong.
I fly an IAS on a non precision approach, check the resulting GS and adjust the VS according to the GS and the table on the chart.
Unless the instructor/examiner is an idiot, he will let you use the GPS for NDB manoevers for anything outside of “CAVOK practise”. Relying on an ADF when a GPS is available is stupid and not justified by anything.
IR examiners have rules from their CAA.
Back to the topic…
Flying a constant IAS (or at least for a time) will generally result in an increasing GS, because on the final approach track you have headwind (usually ) and the wind reduces as you go lower.
And flying an increasing GS, at a constant VS, will place you increasingly above the “glideslope”. This is “safe” but is denying you the opportunity to arrive at the MDA at the MAP, so reducing your chances of becoming visual at the optimal time.
So an optimal approach (no pun intended) would be to reduce IAS, or to increase VS. Either of these will keep you on the “glideslope”, in the face of a decreasing headwind.
The normally taught method is probably to increase VS, because there is a limit to how much you can slow down.
So? If the wind changes I change my VS. But airplanes are flown by IAS, and that’s how I learned to do it. In the end it’s the same anyway, does not matter which factor you change first.
because on the final approach track you have headwind (usually ) and the wind reduces as you go lower.
That’s true for any approach, but a stabilized approach is flown with constant IAS.
