Timothy wrote:
I am not aware of any way to get the VCALC output to drive the glidepath indicator, though it would be neat.
It does on the G1000. If you have a separate autopilot it won’t give a glidepath signal, though.
But in practise during a descent, it’s more convenient to use the VSR (Vertical Speed Required) display than the glidepath indication.
The Visual Approach takes you to the threshold (and not to the touchdown zone, so you would be a little low).
ARP is indeed a dubious aiming point. However, it is usually the midpoint of the longest runway, or the crossing of two runways, and is easily checked on the AIP.
I have an Excel sheet which calculates check altitudes based on runway length. Within reason, taking 100’ off the ARP based calculation is normally quite close.
Obstacles just don’t appear unannounced on the extended centreline that would penetrate a 3° slope. They would have to be 320’ at 1nm or 640’ at 2nm. It is just not the thing to be worried about – a red herring.
Pilot error is the thing to worry about.
And you would never go that low on a DIY approach anyway.
As a last resort procedure into a non IR airfield in IMC, I certainly would prefer it to anything without guidance. As a “normal” way to operate, rather not.
With all the caveats about obstacles, step-down fixes etc., remember SkyDemon’s HSI/pseudo ILS will bring one down to 500’.
The manual states: " the distance instrument will read the distance to the threshold, the time instrument will read the time to the _threshold_".
If one has a stabilized RoD one could go down further to one’s minima; although I have only done this at my ‘home’ field with which I am very familiar.
For most pilots, using an IR(R), or an IR out of currency, ‘500ft’ is perfectly adequate.
I’m rather worried about VFR pilots not understanding the whatabouts of IR approaches, believing it’s just a piece if cake, and then mixing it all up and killing themselves thinking they’ve got it all under control.
In fact there was a twin flying into Mainz which didn’t make the trees, and a Mooney crashing into the taxiway two years ago i’m Zweibrücken, both are suspected to have been self assembled “IFR” approaches; at least looked like it
Sorry Euroflyer to correct you. The twin inbound to Mainz EDFZ you mentioned crashed into the Donnersberg (~2300ft) and 24NM sw of Mainz. The DIY glideslope would have been at around 7200ft.
The Mooney crashed at Saarbrücken airport (EDDR) onto the taxiway, but was flying an ILS – however CAT II weather conditions prevailed at that time.
With all the caveats about obstacles, step-down fixes etc., remember SkyDemon’s HSI/pseudo ILS will bring one down to 500’.
There is also the GPS-ILS app, which is rather controversial in the UK. I tried to find out how exactly the glideslope was generated but the app developer (who got a UK pilot to produce the data) didn’t want to discuss it 
I did some tests with it and while the LOC was spot on, the GS was nowhere near the real ILS GS (tested at EGHH and EGKB). It probably does the same thing as SD, but whether it is better than nothing I am not so sure because you don’t really know whether it is working.
Another fun but inconclusive thread is here. That also seems to be a missed opportunity, but there is probably a reason why nobody does it.
Timothy wrote:
The Visual Approach takes you to the threshold (and not to the touchdown zone, so you would be a little low).
Not true! I have visual approaches on my GTN650, and it mimics the 26ILS very nicely(at my home airfield, however default values seem the norm, the other end is 3.5deg but defaults to 3deg )
From the manual:
Published data is used to determine the visual approach GPA and TCH for
the selected runway. If no published data is available, the default is 3° GPA and
50 FT TCH.
Further it states:
The availability of vertical guidance advisories for visual approaches is
dependent on terrain and obstacle obstructions along the approach path.
If no known obstructions are within the approach path, vertical guidance is
provided to a maximum distance of 28 NM from the runway. If there are known
obstructions further than 3 NM, but within the 28 NM maximum distance from
the runway along the approach, vertical guidance is limited to the approach path
portion after crossing the known obstructions. This is indicated by the shortened
magenta line on the map after loading the approach. If obstructions are within
3 NM to the runway, along the approach path, advisory vertical guidance is not
provided. Lateral guidance is always provided for visual approaches.
Ah, ok, thanks. I’ll try it on the sim.
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.
Presumably it’s an attempt to mimic ILS & LPV, (which it does nicely at the ones I’ve flown so far), for me, anyway, 600m would be the exception and allowances made.
IF one intends to use this in anger, then flying it visually first might be a good idea!
Sadly the CAA’s dire lack of progress with GPS derived approaches in the UK may encourage some to go this route…..Shame they arn’t acceptable for PBN sign off bull! ;-)
