The location and height of the GS antenna is irrelevant – the signal you are following is bounced off the ground. I could bore you with details of SBO, course beams, active arrays etc. The point is that the GS is unreliable below a certain height (let’s say about 50ft for argument’s sake) and if your autopilot is merrily flying the approach you will likely get a nasty little fly down just as you cross the threshold. Hence the reason that proper Cat III autopilots actually disconnect the GP guidance at 50ft radalt (have you got a radalt?) and then fly a radalt ‘controlled’ two stage flare and landing manouevre.
So, getting back to a GA aircraft scenario, a Cirrus doesn’t have any of that fancy kit. If you are flying an ILS on AP you will need to decide when to take manual control before the AP tries to kill you.
ILS is so 1950s… LPV is 1000x cheaper and doesn’t have any of those problems. If we only had it everywhere…
Agreed, but find yourself a Cat IIIB, or indeed a Cat II, LPV approach. I think it (GAST-D) will come in the next few years but GA will still be faced with an equipment (cost) and training dilemma.
Very interesting discussion. Im N reg, part 91, FAA lic.. In the US I can do an approach even if its below minimums because the airport equipment does not always reports what the pilots eye balls see. For instance flying into a setting sun is infinity more difficult than on a dark night with HIRL on max and with a rabbit lead in. The RVR is the same in both situations but yet I would go miss on the daylight approach. The conditions dont happen often just an example of its what you see in the cockpit that counts.
So can I attempt an approach?
So can I attempt an approach?
If at the outer marker/1000ft RVR or converted met vis is below the relevant limit, no. Or more accurately, you can attempt whatever you like but not legally.
The location and height of the GS antenna is irrelevant – the signal you are following is bounced off the ground. I could bore you with details of SBO, course beams, active arrays etc.
Please do. I’d be very interested in how you argue antenna location away.
Anyway, I’d be interested in how common image type glide slope antennas still are, given that they need a large reflecting area on the ground, and thus a large critical area and apparently they’re affected by snow quite a bit, the glidepath is said to change by 0.3° per meter of snow…
Skellefteå (ESNS) is one place the AIP cautions the GPA may be greater than 3° in winter due to ice and snow around the glide path array.
LPV is 1000x cheaper
So… Achim… evidently you are a man of substantial means so I accept Paypal 
Now transpose that retrofit cost to all aircraft which
Currently, most AOC ops cannot even fly a GPS/LNAV approach, never mind a GPS/LPV…
etc
Peter, the first three seem to be a unique UK problem, the rest of europe already had to upgrade to 8.33kHz for any meaningful IFR capability, and point four seems to apply to one person only 
Very funny
So, what % do you think of ILS capable IFR aircraft, light GA, non-UK based, can fly LPV low?
8.33 is relatively trivial compared to LPV, in cost.
Anyway, LPV still doesn’t allow Cat3. It should fly you to the runway, I guess, at -500fpm or so. Then you still smash up the landing gear. ~5kt VS, pretty likely. Or you will get a massive bounce, or break the nose gear.
