Thanks guys think I got it all now finally.

Thank you all!

So then I was correct and you should use Radio and QFE for ILS approaches?

There are basically 3 kinds of approach.On the most basic kind, which would normally be an NDB approach, but might also be a VOR approach where the DME is U/S or your receiver has failed, you are simply going to establish outbound from a beacon, fly the outbound track (the QDR) for a given time, then turn inbound towards the runway, descend to the MDA (minimum descent altitude), then fly along level until you hit the MAP (missed approach point), since you have no idea how far you are from the beacon/runway/MAP you fly level until the needle swings round as you cross the fix, then if you have not acquired the necessary visual references to land, you will go around from the MAP. For this to work the beacon has to be on the airfield otherwise it wouldn't be a sensible MAP. Most beacons are on airfields anyway, but it's possible you'd find some that aren't, but they wouldn't be useful for this kind of approach.It used to be the case that a regular non-precision approach WITH a means of measuring distance (NDB/DME, VOR/DME, RNAV) would be flown the same way - dive and drive. You'd descend to the MDA, level off, fly along and if you didn't see the lights/runway/other reference, you'd go around from the MAP. Now, these are flown as CDFA (Constant Descent Final Approach), meaning the plate shows a "glidepath" (it's not really a glidepath, because there is no vertical guidance on a nonprecision approach, but it's a bit like one in that there is a specified vertical path). The plate gives distances and altitudes, so as you cross the FAF at the specified platform altitude and start your descent at a rate that matches your groundspeed, you then adjust your rate of descent as necessary to try and keep to the specified profile vertically, while tracking laterally using whatever type of approach aid it is. Non-precision plates will also often have step down fixes which are shown as grey shaded blocks under the profile on the plate, these are mandatory "not below" points. The profile itself is advisory, but the point is that whether you fly exactly the same profile as the plate or not, you fly a stable, fairly constant descent. Then, when you hit the MDA you go around (actually you start going around at MDA+50', since the MDA is a mandatory "not below", and as you add power and pitch up to go around you will go slightly below the altitude at which you begin going around, so you add 50 feet to the MDA so you don't bust it). Reaching the MDA has become the MAP.There is no level flight segment at the MDA in a CDFA approach which essentially means for all practical purposes, since purely NDB approaches without DME are a relic and rarely seen, that you go around as soon as you finish descending. Therefore, so you have the best chance of seeing the runway and landing off the approach, you try and ensure you end up at minumum altitude at the right point in terms of distance to go - otherwise, if you hit MDA an extra mile further out, you may well not see the runway environment in bad visibility so you'd have to go around, when you might have been able to see the runway environment and land if you'd been at the same altitude another mile further along.Provided you are not below a stepdown fix the profile you fly on a nonprecision approach is not mandated legally, but in airline operations company SOPs will specify that the approach must be stable, that high rates of descent near the ground are forbidden, that adjustments to ROD once established may not be more than eg +/- 300fpm etc. In private flying you could for example be 500 feet high with a mile left to go and just dive in at 2000fpm ROD if you so wished as long as you didn't bust a stepdown fix or the MDA, but your days of performing non-precision approaches might well end sooner than you'd like...Both of the approach types above are flown with the barometric altimeter down to an MDA. The MDH (height above ground) is provided on the plate, but you never operate with QFE set, always QNH, so if the runway elevation is 5000 feet above sea level, and the MDH is for example 400 feet, you would see 5450 feet on the altimeter when you started going around. Your altimeter is showing you altitude above sea level, not height above ground, and your minimum is an altitude not a height.CAT I ILS is also flown on the baro altimeter (QNH), but is a precision approach - there is a glidepath which you follow, so there is no checking altitudes against distance to go (although there is sometimes a glidepath check stated on the plate, which gives you a single pair of distance + altitude, so you can ensure you've intercepted the correct glidepath, and no the "phantom" glidepath which appears above the real one at a much steeper angle, which is why the glidepath is always intercepted from below - so you intercept the correct one). When LPV RNAV approaches get regulatory approval in the EU there will also be precision GPS approaches with the GPS providing both lateral and vertical guidance, I believe in the USA they already have these, but in Europe all RNAV approaches are nonprecision at the moment.Precision approaches are flown to a DA (decision altitude) which is the altitude at which you make the decision whether to go around or land - given that you will descend below the DA during the process of looking up, deciding that you don't have visual reference, adding power and pitching up to go around, the DA is _not_ a minimum altitude in the way that an MDA is - an MDA you absolutely do not descend below, a DA you may descend slightly below as you go around, but that is expected and allowed for in the design of the procedure. You never bust it intentionally, you make you decision _at_ the DA, but the process of going around may result in dipping slightly below it.Again, all flown QNH, so if field elevation above sea level is 5000 feet, and DH is 200 feet, then DA is 5200 feet on the altimeter.On an ILS you must not, once established, go outside of half scale deflection of the localiser or glidescope otherwise you've missed the approach and must go around. Contrast this with a nonprecision approach where all you _must_ do vertically is not bust the stepdown fixes or MDA.CAT II and CAT II ILS are the only approaches I'm aware of which have radio minima - the radio altimeter, which bounces radar off the terrain below the aircraft to measure the actual _height_ above ground, is used and minima are 100 feet or more for CAT II and 0 (the ground) for CAT III. Maybe there are others - I'm not sure if anywhere actually uses MLS, if so maybe there is a CAT II or III MLS approach somewhere with radio minima, but I don't know of any. Note that as mentioned above for this to work you must have flat terrain in the undershoot, so the indications you get from the radio altimeter can be relied upon. There are other regulatory requirements for CAT II and III to do with lighting, sensitive altimeters, multi crew ops etc.CAT II or III ILS approaches will still be flown with the barometric altimeters set to QNH, so what you'll see on the PFDs and ISFD will be altitude above sea level, but the "minimums" callout will be determined not by barometric altitude but by radio height.As far as I'm aware QFE is mainly used by the military. Why? I have no idea, probably historical reasons. As stated above, with QFE set your altimeter shows you _height_, not altitude. Of course it can only show height from one datum, the field elevation, so is useless elsewhere.

Just a note, The baro or radio mins will depend on the type aircraft you fly. Basically the BARO and the radio mins will be at the same height above the runway when the altimeter setting is correct. When i flew DC-10s, we would set the radio to the agl number and set the altimeter bug to the baro. On modern aircraft, like the G-5/550, we set the BARO. A technique we used when we had g-3s was this. Big number big jet(G-5/550) and little number little jet(G-3). In the G-3 we would always set the agl mins because that jet didnt have the capability to anounce minimums based on BARO minimums. It didn't have a altimeter bug. In the G-5, it could precisely call mins from a BARO setting. It has the option of setting BARO or radio in the display controller. The only time we set the radio altimeter in the 5/550, is during a cat 2 app.