We had some discussions in other threads (here) about a flight I made to Donaueschingen and I could not provide all the exact details. Today I had to go there again (to collect my landing tax from last time which was invoiced twice but that’s a story for another thread) and I wanted to write with my memory still fresh.
The flight plan was LSZH0930 N0142F060 ZUE2V ZUE Z601 TRA TRA3D EDTD0028. Takeoff was as normal, at 5000ft (minimum vector altitude) I got some vectors and then “Climb to 6000ft and resume own navigation to ZUE”. Then at some point before ZUE I received further vectors and then “Direct TD003”. Some time later it was “Cleared for the RNAV approach 36 in Donaueschingen with a visual righthand circuit for 18”. This time I asked explicitly: “Is this a clearance for a straight-in approach via TD003 and VEBEV?” to which the answer was (in these words) “If you wish you can make a straight-in approach or otherwise advise your intentions”. I understood this as “That’s what I am giving you but if you are unhappy with it, let me know”. I confirmed straight-in to which I got this new clearance: “Cleared for the straight-in RNAV approach 36 with a visual righthand circuit for 18. Maintain 6000ft to TD003”. So the descent is from TD003 at 6000ft (1000ft above the Jeppesen chart altitude) down to 4500ft at VEBEV (4.0nm) and then down to 3200ft (circuit altitude). At 145kt
Here is the track planned and the one flown:
Now about my problem and question. I had the GNS 430 programmed as follows: Flight plan from LSZH to EDTD, departure ZUE2V, arrival TRA3D and approach RNAV 36 from TRA. Everything is fine until I get the direct to TD003 which is a point of the approach. So I go in the flight plan, select TD003 and make a direct to it. I also see the flight plan moving the current leg to the one going to TD003. I cannot select “Activate vectors to final” at that point because that removes my direct to TD003. Then at TD003 (or maybe after it). I get a message “Approach not active”. So I go and select “Activate approach”, I confirm it and I get the same message: “Approach not loaded”. I tried to use “Activate vectors to final” which threw me away and back before TD003. I didn’t have much time to play with it so I again selected “Activate approach” with the result that the track turned magenta but I got again “Approach not loaded”. It seemed like I was getting the normal lateral guidance but the GNS 430 was complaining. I was visual all the time (almost summer time here) so it was no problem and I could play with the device a bit but in real IFR that would be very unpleasant. I haven’t done any RNAV approach where I join at an intermediate point during my training and obviously I couldn’t get it to work correctly neither last nor this time. Does anyone know what the right procedure in this case is to make the GNS work as expected?
I had a camera on my headset during the approach so I can probably try to figure out the exact order of events and messages in case some details are incorrect but in general my problem remains that I am unable to load that RNAV approach after TD003.
I have found an old discussion on COPA about this. It seems to be a bug of the GNS430 that was supposed to be fixed in 2005 already. I don’t know if I’m allowed to extensively copy & paste the discussion from COPA here; at least here is the gist of it, please remove it if it is deemed inappropriate. But I think it is in the interest of safety to spread the word:
1. The message is generated if the track diverges from the final approach course by more than some angle when abeam the FAF.
2. The criterion for generating the message is considered a bug and will be changed with the next firmware release. The release will coincide with the release of the terrain awareness and warning system (TAWS), but will not require the purchase of TAWS capability. The release is expected in the next several months.
3. The appropriate pilot response to receiving the message is to fly to the missed approach point, without descending, and to fly the missed approach, or as otherwise instructed by ATC.
4. There is nothing magic about being within 2 NM of the FAF. This is simply the distance over which the unit normally increases CDI sensitivity from 1 NM to .3 NM. It is possible to load, activate, and fly an approach within 2 NM of the FAF, if all other criteria are met (RAIM, etc.). The unit will simply use the available distance to the FAF to increase CDI sensitivity as fast as it needs to to get to .3 NM at the FAF.
But so much for this statement from another thread:
Flyer59 wrote:
it really doesn’t happen that an RNAV approach in an SR22 “doesn’t work”
Edit: The post on COPA is actually in the open section.
Another question: After TD003, did you follow the published approach, i.e. did you fly to VIBEV (FAF)? Because as I understand it, you need to be on a published segment of the approach 2.0 nm before the FAF in order for it to activate (not too far off the centerline). You have 4.0 nm between TD003 and VIBEV, which should be enough for the approach to activate if you are on the right track.
One thing to remember in IMC is to declare a missed approach early if you have a “what’s it doing now?” moment. Ask me how I know… that was my takeaway from my last approach which I hadn’t set up correctly. I quickly tried to disconnect the flight director (I was hand-flying with FD), re-engage it, re-program the approach twice and finally made it to a very stabilized approach almost to minimums, but in hindsight I am not happy with my course of actions. It is just not safe to start programming your avionics when you are hand flying in IMC under pressure.
Yes, I flew to VIBEV and got again the message (after clearing it by reading it) after VIBEV.
About the safety, I had the same issue last time I flew the route so I expected it and wanted to deal with it to be able to understand it. I also knew that today I have no problem landing visual if needed, so safety was assured. Of course in 4nm there is not a lot of time so I tried only a couple of times and then concentrated on the approach and landing.
Was that on the intro flight with Mark? If so, that is a GNS430W, which might be different than the normal 430.
I wonder if the activation did not work because of the direct onto an approach waypoint. But it is really interesting what happened here and i’d love to get to the bottom of this.
No, it was with the Seneca II. Unfortunately I don’t know what software version the 430 in it has.
Is it a normal 430? W?
If you fly vectors you should still select an IAF, fly in HDG mode and select the next leg in the FP. If the next direct is to a point in the approach you do not need to press activate, just fly in HDG mode. When you get the clearance you switch to HDG+NAV or APP mode, depending on A/P and it will capture the final by itself.
Is that how you do it? Maye i don’t understand ..
It’s a 430.
Yes, that’s how I do it in a normal situation when I have a self line up or vectors. In this case I was first in NAV mode (with the direct to TD003) which I then changed to HDG and then I flew manually. But I didn’t arm APP mode at any time. That should not affect the activation of the approach on the GNS 430 though, should it? I mean, I can fly the whole thing without the A/P and it should still be ok.
No, of course not. I just realized that at one point who were speaking about “load approach” and then about “activate approach”. You do not have to activate the approach if you activate a LEG that’s part of the approach.
That’s my error. I always meant activate, not load. Also the message was “Approach not activated”.
