PeteD wrote:
Sadly the CAA’s dire lack of progress with GPS derived approaches in the UK may encourage some to go this route.
Actually, one has to wonder which is safer, a procedure established in uncontrolled airspace with no radar no procedural service, where aircraft are channeled into very narrow Initial Segments, or a pseudo random approach from a notional IF. Just a thought.
I have now flown the GTN on the Sim using the visual approaches into each end of Fairoaks (sorry, Heathrow, I hope I didn’t upset your flow too much 
) and I can tell you that PeteD is quite right, from both ends the GP takes you approximately halfway down the runway. To get the threshold you need about two dots low on the slope.
Incidentally, I thoroughly recommend XP11 + Reality XP for this kind of thing. You can really push it and learn some stuff without causing any danger or inconvenience.
I am always happy to host anyone in the SW London area who wants to come and play and try things. In some ways an hour on the sim is worth five on the aircraft, and is completely free (we even have solar panels 
)
It does occur to me to wonder whether there is any database element to the Visual Approach.
I mean, is the GTN calculating what is effectively the FAS Datablock, and determining whether the terrain and obstacles justify a glidepath from scratch from raw runway data every time? Or is there somewhere a database, if so where? It sure ain’t Jeppesen, so it isn’t being updated.
If it is building it from scratch on the fly, as I suppose, it does make the £50k a shot AIP designers look a little dear!
I don’t really see a problem with Garmin’s Visual Approach glide slope ending 50 ft above the TCH. Most AIP runways are more than twice as long as needed by ordinary SEP aeroplanes.
And, just supposing we’re brave enough to fly this “visual approach guidance” in IMC down to 200 ft AGL; we’re still half a mile from the threshold. If that’s not enough distance in which to slip away an extra 50 ft, we’re either in some rocket ship which has no business flying that approach or we need some practice with Langeweische’s book.
It seems odd though, as 50ft is going to take you 300m into the runway, which would not be what you would want at a 600m runway.
If I remember correctly the 50ft TCH is exactly what a standard ILS/GP is adjusted to according to ICAO Annex 10. So they don‘t do it differently than the ILS.
Yep, so works fine, we’re not doing cat 3b into this 600m strip!
I’ve been away from EuroGA for a while (used to post as ValerioM), and which better thread to resurface again! DIY ILS-like approaches have always interested me. I currently fly an RV7A with G3X Touch+GTN750+GMC307 (+G5+GNC255 as backups). The plane also has double Alternators, GTS800 TCAS and a Ballistic Parachute (all rare options on an RV7). After two SR22 (Avidyne and G1000) I wanted to try the Experimental world getting an ideal plane that simply didn’t exist in the certified world: a 1) fast, 2) aerobatic, 3) IFR-capable plane, with 4) ballistic chute, with 5) good range/useful load, 6) grass strips friendly and 7) can run on Mogas. I lost the 4 seats option, but didn’t use the back seats much on 400hrs of SR22 anyway. Back to the thread theme, the GTN750 currently offers “VFR approaches” (ie, “de facto” GPS precision approaches) to almost any airport, I think all with 3 degrees slope (didn’t test any mountainous airport yet), and fully coupled with the AP (to be used as guidance in VMC only, of course). The G3X+GTN system also offers the VCALC function, already described in a previous thread, which allows to program a fully AP-coupled GPS approach to ANY waypoint (eg a grass strip), but with the limit – already discussed – that the slope angle cannot be controlled very well (while the G1000 allowed for explicit slope angle input to ANY waypoint). To be honest I’ve not yet understood if the G3X plays a crucial role in making the GTN750 VCALC function a Flight Director/AP function as well, and not just a calculation/advisory tool. All in all I preferred the G1000 to the G3X+GTN, and the only improvements of the G3X+GTN are a) the touchscreens and b) maps show VRPs which are crucial for VFR flying in Europe. Also, the G3X offers “flight envelope protection” which my SR22, being older than 2010, didn’t have.
If I remember correctly the 50ft TCH is exactly what a standard ILS/GP is adjusted to according to ICAO Annex 10. So they don‘t do it differently than the ILS.
But few 6-800m runways have ILS.
I guess we have ask ourselves where we touch down after a VFR approach to a 600m runway and a 2000m one?
I think that, at least with average IFR capable aircraft, we are unlikely to aim 300m into a 600m runway. Indeed, in a Mooney, Bonanza or DA42 I think that you would be unable to do it twice.
You could argue, of course, that that is exactly why instrument runways are longer, and that is why LPVs should not be permitted to short runways, but the counter argument might be that if we are going to put glidepaths onto short runways then we should point them at the threshold.
Timothy wrote:
if we are going to put glidepaths onto short runways then we should point them at the threshold.
Shorter runways should have steeper glidepaths. With a 3.5° glidepath (max permitted) you save 50 m. And then landing distances data already assume crossing the threshold at 50’. I am well aware that you can get into shorter runways by crossing the threshold at a lower height and/or having an even steeper descent, but is that really a good idea in IMC?
