Airborne_Again wrote:
Shorter runways should have steeper glidepaths.
We are stuck with 3° in this context
3.5° glidepath (max permitted)
Really though?
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?
I think that the whole question of whether any of this is a good idea in IMC is moot. You are certainly not going to be doing it to low minima (RVR or DA) to a short VFR runway (I hope!) because there will be no approach lights.
But, leaving aside for the moment the very big question of whether these things are a good idea or not, and accepting, for the moment, that we are discussing how they would be best designed and executed if they were a good idea, where, given a 3° approach to a 600m runway, would be the best aiming point for the GP? I would say that that would be the threshold, allowing a stable approach and no manoeuvring at DA.
About the question of which area of the airport are “pointing to” the VFR Approaches offered by the GTN (or G1000), I think they point to Airport Coordinates shown on each Airport Chart, and not the relative Threshold coordinates. In most airports I’ve been, the Airport Coordinates are exactly the center of the runway, but not sure this is a legal requirement of every official chart. I had an argument with Italian CAA about Foligno Airport (a 1700m tarmac airport) having published Airport Coordinates falling well outside the runway, and pointing out that those coordinates are used by Garmin and Jeppesen to code their “VFR Approaches” to Foligno, but they answered that any point of the airport is sufficient accuracy for the Airport Coordinates (does anybody know if ICAO prescribes a different rule about this?). In my opinion, this topic is important especially if one plans landing into a VFR airport close to Civil Twilight: you want the VFR Approach guidance to help you VERY close to the numbers, especially if the airport has no lights.
See my post #18, the manual states the aiming point, there is no question.
didn’t see, sorry. So “50 FT TCH” means 50ft above the relative Threshold I guess. I must confuse with VCALC which is pointing to the runway center, I think. In reality one starts hand-flying well before threshold, so difficult to notice the difference (except that in Foligno you would be WAY out of the runway centerline if following the VFR Approaches, both the “official” ones and the VCALC ones.)
mancival wrote:
the VFR Approaches offered by the GTN (or G1000), I think they point to Airport Coordinates shown on each Airport Chart
That is not what the manual says. As @PeteD quoted above, they point to a TCH of 50’.
I have tested the assertion on the sim.
Prestwick 03 is a long way displaced from the ARP, but the GTN takes you to a touchdown point on the centre of the runway:
Timothy wrote:
Really though?
That’s what PANS-OPS says…
The minimum for this procedure is not lower than 1550’ above threshold and the chart indicates a substantial visual segment at the end of final approach so in that case the limitation might not apply.
Timothy wrote:
But, leaving aside for the moment the very big question of whether these things are a good idea or not, and accepting, for the moment, that we are discussing how they would be best designed and executed if they were a good idea, where, given a 3° approach to a 600m runway, would be the best aiming point for the GP?
Well if we are discussing other aiming points that what the Garmin units give us, why not also discuss other glide path angles?
mancival wrote:
didn’t see, sorry. So “50 FT TCH” means 50ft above the relative Threshold I guess.TCH = Threshold Crossing Height.
I must confuse with VCALC which is pointing to the runway center, I think.If the waypoint you are descending towards is the airport itself (as opposed to a runway), the coordinates will be that of the Aerodrome Reference Point (ARP). This will usually — but not always — be at the geographical center of the runway system. So with a single runway, the ARP will usually be at the middle of the runway.
Note the “usually”. Once published, the ARP is not supposed to be changed even if the runway system changes. So if a single runway is extended at one end, the ARP will no longer be at the middle. If an airport used to have several runways but have closed all but one, the ARP may well be a substantial distance away from the remaining runway.
Indeed.
Thanks Airborne_Again about the ARP explanation. Now I finally understand why Garmin, with the GTN, decided to go the lenghty way of creating “official” VFR Approches rather than providing a general vertical navigation tool to any waypoint like in the G1000. Still would be nice to program any slope to any waypoint, since Garmin database doesn’t include many smaller strips.
